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12

Chemistry SCH4U

This course enables students to deepen their understanding of chemistry through the study of organic chemistry, energy changes and rates of reaction, chemical equilibrium, atomic and molecular structure, and electrochemistry. Students will further develop problem-solving and laboratory skills as they investigate chemical processes, at the same time refining their ability to communicate scientific information. Emphasis will be placed on the importance of chemistry in daily life, and on evaluating the impact of chemical technology on the environment. Prerequisite: Grade 11 Chemistry SCH3U

Recall of Basic Chemistry

Polarity of Bonds

Which of the following bonds is most polar? Solution
Polarity is directly proportional to the difference in electronegativity

O-H
Oxygen electronegativity = 3.5, Hydrogen electronegativity = 2.1
Electronegativity Difference: 3.5 - 2.1 = 1.4

Na-F
Sodium electronegativity = 0.9, Fluorine electronegativity = 4.0
Electronegativity Difference: 4.0 - 0.9 = 3.1
The highest polarity is between the metal and non-metal with the greatest electronegativity difference.

H-Cl
Hydrogen electronegativity = 2.1, Chlorine electronegativity = 3.0
Electronegativity Difference: 3.0 - 2.1 = 0.9

Mg-Br
Magnesium electronegativity = 1.2, Bromine electronegativity = 2.8
Electronegativity Difference: 2.8 - 1.2 = 1.6

B-F
Boron electronegativity = 2.0, Fluorine electronegativity = 4.0
Electronegativity Difference: 4.0 - 2.0 = 2.0

Types of Bonding

Answer the following question on the different types of bonding.

What is an ionic bond? [3] Solution
Hint Clear Info
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Hint Unavailable
Ionic bonds form when electrons are transferred from the positive cation to the negative anion. These oppositely charged atoms are attracted (electrostatically).

Describe what makes a covalent bond non-polar. [3] Solution
Hint Clear Info
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Hint Unavailable
  • Low electronegativity difference between the atoms,
  • ...results in relatively equal sharing of the bonding electrons,
  • ...results in negligible dipole moment (polarity).

Units: Mass and Volume

1.0 kg equals: Solution
Hint Clear Info
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g
Hint Unavailable
1.0 kg = 1,000 g

1 mL equals: Solution
Hint Clear Info
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cm3
Hint Unavailable
1 mL = 1 cm3.

(1,000 L = 1 m3)

Lewis Structures

Draw the lewis structure for NO31-

Draw a lewis structure for CH4

Naming Multivalent Metals

Iron has two different charge states, iron(II) and iron(III). When referring to the charges on an element, the name can be ferrous, in which the suffix -ous refers to: Solution
-ous is a lower charged state, whereas -ic is a higher charged state. Be careful, "-ous" does not always refer to a +2 charge. It is a relative term, and the magnitude depends on the element.

Naming Compounds

Name the hydrate: CuSO4·5 H2O Solution
Copper is multivalent, therefore name using the stock naming system to indicate the charge with a roman numeral...
The amount of waters is named with the prefix system... 5 is penta...
copper(II) sulfate pentahydrate

Periodic Trends Review

On the periodic table, atomic radius decreases Solution
Up a group (because less energy levels), and left-to-right across a period (because higher nuclear/valence charge).

Classifying Types of Reactions

Which of the following is a combustion reaction? Solution
Types of Combustion Reactions

Carbon + Oxygen → Water + Carbon Dioxide
Non-metal + Oxygen → Non-metal Oxide
Metal + Oxygen → Metal Oxide

The following reaction is a... Solution
In this single displacement reaction, the non-metal replaces the non-metal.

Molecular Weight

Calculate the molecular weight of ammonium sulfate in the following reaction, rounded to the nearest whole number. Solution
Hint Clear Info
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g/mol
Hint Unavailable
Ammonium sulfate, (NH4)2SO4:

N × 2
H × 8
S × 1
O × 4
= 132 g/mol

Review Chemical Formulas: Criss-Cross Method

The chemical formula of aluminum chloride is: Solution
Balance the charges, Al3+ & Cl1-...

AlCl3

Balancing Chemical Equations

Write a balanced chemical equation for the following reaction: Solution Iron + Copper(II) Sulfate → Copper + Iron(II) Sulfate
Hint Clear Info
+
+
Incorrect Attempts:
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Hint Unavailable
Fe(s) + CuSO4 (aq) → Cu(s) + FeSO4 (aq)

Reactions

Solid aluminum reacts with aqueous hydrochloric acid in a single displacement reaction. Given these reactants, complete the reaction equation and balance it. Solution
Hint Clear Info
+
+
Incorrect Attempts:
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Hint Unavailable

Mass and Moles

Determine the molar mass of gold(III) trinitrate Solution
Hint Clear Info
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g/mol
Hint Unavailable
gold(III) trinitrate = Au(NO3)3:

Au × 1
N × 3
O × 9
= 501 g/mol

How many moles are in 39.0 g of NaCl? Solution
Hint Clear Info
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mol
Hint Unavailable
First calculate the molar mass of NaCl is 58.44 g/mol...

Mass and Moles

Calculate the unknown quantities in each of the following questions.

How many moles of oxygen atoms are in 3.0 mol of aluminum oxide? Solution
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mols
Hint Unavailable
Al2O3 has 3 oxygen atoms per molecule. Given 3 mol of the molecules there are 3 x 3 = 9 moles of oxygen atoms.

Determine the mass of 4.5 mol of H2CO3 Solution
Hint Clear Info
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g
Hint Unavailable
= 279 g

Determine how many molecules are in 10.0 g of NaCl given Avogadro's constant: 6.02 × 1023 particles/mol. Solution
Hint Clear Info
× 10
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molecules
Hint Unavailable
= 1.03 × 1023 molecules

Empirical and Molecular Formula

A molecule contains 85.7% carbon and 14.3% hydrogen.

Determine the empirical formula. Solution

¹

²

³

Incorrect Attempts:
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Hint Unavailable
CH2 (Solution not shown)

If the molar mass of the compound is 56 g/mol, determine the molecular formula. Solution

¹

²

³

Incorrect Attempts:
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Hint Unavailable
C4H8 (Solution not shown)

Determining the Limiting Reagent

Given 50 slices of bread, 24 leaves of lettuce, and 84 slices of cheese, determine the limiting ingredient in the following recipe: Solution 2 Bread + 1 Lettuce + 3 Cheese → 1 Sandwich
Bread
Can make 50/2 = 25 sandwiches with the starting amount.

Lettuce
Can make 24/1 = 24 sandwiches with the starting amount.

Cheese
Can make 84/3 = 28 sandwiches with the starting amount.

Therefore the lettuce is the limiting ingredient.

In the imaginary reaction below, 10 mol of AB, 15 mol of CD, 6 mol of EF, and 16.5 mol of G react, which reactant is limiting? Solution 4AB + 5CD + EF + 3G → 2HI + J + 8K
The lowest numer is limiting.
AB: 10/4 = 2.5
CD: 15/5 = 3.0
EF: 6/1 = 6
G: 16.5/3 = 5.5

Therefore AB is the limiting reactant

Determining the Limiting Reagent

Given 100g of HCl and 100g of CaCO3, which of the following will be consumed first as the limiting reagent (reactant)? (Careful: don't forget to balance your equation first.) Solution
Don't forget to balance first. Second: convert mass to moles.
Third: Divide moles by the stoichiometric coefficient - the lower number is from our limiting reagent.
Since CaCO3 has a lower ratio, then it is the limiting reagent.

Stoichiometry: Theoretical Yield

If O2(g) is in excess, and 42.0g of C2H4(g) is consumed in the following reaction, determine the theoretical yield of CO2(g). Solution
Hint Clear Info
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g
Hint Unavailable
Since there are only two reactants and one of them is in excess, then the theoretical yield has to be based on the only other reactant → C2H4(g).

1st, convert mass to moles: 2nd, use the stoichiometric ratio of C2H4 to CO2. 3rd, convert moles to mass:

Percent Yield

If 50.0 g of K2S reacts with excess zinc chloride to produce 40.1 g of zinc sulfide, determine the percent yield of the precipitate. Solution
Hint Clear Info
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%
Hint Unavailable
Since there are only two reactants and one of them is in excess, then the theoretical yield has to be based on the only other reactant → K2S.

1st, convert mass to moles: 2nd, use the stoichiometric ratio of K2S to ZnS. 3rd, convert moles to mass: 4th, calculate percent yield

Units: Solutions

In solutions chemistry, the unit 'M' refers to Solution
Capital 'M' stands for molarity, which is the unit of concentration. This is the same as mol/L.

Calculating Molarity

Determine the molarity (molar concentration) of 1.0 mol NaCl dissolved in 250 mL of water. Solution
Hint Clear Info
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mol/L
Hint Unavailable
Although 1 mol NaCl dissociates into 2 mols of ions: Na+ + Cl-, the molar concentration uses the mols of the solute, or compound instead of the total ion equivalent.

The concentration of chloride anions (Cl-) in 1.0 mol of MgCl2, dissolved in 1.0 L of water is 2 mol/L Solution
MgCl2 dissociates into 2 chloride (Cl-) ions: 1.0 mol of MgCl2 dissolved in 1.0L of water = 1 mol/L MgCl2.

Since there are every 1 MgCl2 forms 2 Cl- ions, then the molarity of chloride anions (Cl-) = 2(1 mol/L)
= 2 mol/L

Calculating Molarity

Determine the mass of potassium nitrate (KNO3) required to make 1,250 mL of a 0.50 M solution. Solution
Hint Clear Info
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g
Hint Unavailable

120 mL of 4.5 mol/L potassium fluoride (KF) is added to 100 mL of water. Determine the new molarity of the solution. Solution
Hint Clear Info
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mol/L
Hint Unavailable

25 mL of a 4 mol/L solution is used to prepare a 2.5 mol/L solution. Determine the final volume in milliliters. Solution
Hint Clear Info
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mL
Hint Unavailable

Net Ionic Equation

Determine the net ionic equation for the reaction below. Show your work in your own notes. Solution
Separate the ions of all soluble compounds (leaving the solid, liquid, and gases).

Cancel ions on the left and right side, leaving:

Acids and Bases

Which of the following is a strong acid? Solution
This year you should memorize the 6 most common:
6 Most Common Strong Acids
HClHBrHIHNO3H2SO4HClO4

Which of the following is a monoprotic acid? Solution
"Monoprotic" means there is 1 (mono) acidic proton in the molecule.

Of the answer choices, acetic acid CH3COOH has only one acidic proton and forms the acetate ion plus one proton: CH3COO-1 + H+

Conjugate Pair of Acids and Bases

Which of the following is a conjugate acid-base pair? Solution
The carbonic acid H2CO3 dissociates into the bicarbonate anion, which forms a salt with the available sodium ions, as sodium bicarbonate: NaHCO3

Solutions of Acids and Bases: Monoprotic Neutralization

A 3.33 L sample of 8.88 mol/L nitric acid (HNO3) is used to neutralize what volume of 4.44 mol/L potassium hydroxide (KOH)? Solution
Hint Clear Info
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L
Hint Unavailable
Neutralization equation:

Thermochemistry: Endothermic and Exothermic

A reaction that causes the temperature of the system to decrease from 12.˚C to 5.4˚C is endothermic. Solution
Endothermic reactions absorb heat energy, causing the temperature of the system to decrease. Exothermic reactions release heat energy, causing the temperature of the system to increase.

Converting Kelvin and Celsius

Convert 273K to Celsius: Solution
Hint Clear Info
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˚C
Hint Unavailable
Celsius = Kelvin - 273

Kelvin = 273K - 273

= 0˚C

Definition of Specific Heat

Specific heat is defined as Solution
Specific heat is

The energy required to raise the temperature of one gram by 1˚C

Specific Heat

12 kJ of energy is added to water causing the temperature to increase from 296K to 343K. If the specific heat capacity of water is 4.18 J/(g·˚C) determine the mass of water. Solution
Hint Clear Info
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g
Hint Unavailable
q = mc(T2 - T1)
Make sure to use Joules and not Kilojoules in the equation...
Change in temperature can use either Kelvin or ˚C because the magnitude of the change is the same for both.

Gas Laws

Which of the following is Charles' Law? Solution
Charles' Law:

Gay-Lussac's Law:

Avogadro's Law:

Boyle's Law: P1V1 = P2V2

Ideal Gas Law: PV = nRT

Dalton's Law of Partial Pressure

If 12 kPa of O2 gas is mixed with the following gases in a 20 L container, determine the total pressure if they do not react: 20 kPa CO2, and 30 kPa N2. Solution
Hint Clear Info
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kPa
Hint Unavailable

Ideal Gas Law

Determine the temperature of 10.0 g of carbon dioxide gas (CO2) in a 500mL container at 1.5 atm. (R = 8.31 kPa·L/mol·K) Solution
T =
Hint Clear Info
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K
Hint Unavailable
First convert all units to those used in 'R': kPa·L/mol·K
500mL = 0.5L
1.5atm =
Convert 10.0g of CO2 to moles:

Plug into equation to solve for T.

Molar Volume

At STP (0˚C and 101.3 kPa), the molar volume of a gas is 22.4 mol/L. Determine the volume that 50.0 g of fluorine gas occupies. Solution
Hint Clear Info
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L
Hint Unavailable
Convert to mol, Use molar volume at STP:

Stoichiometry with Gases

100 g of nitrogen gas combines with excess hydrogen in the following synthesis reaction at (0˚C, 101.3 kPa, 22.4 mol/L), determine the mass of ammonia produced. Solution
Hint Clear Info
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g
Hint Unavailable
First: Convert mass to moles Second: Use the stoichiometric ratio Third: Convert moles to mass

Flashcards: Basic Review

How many electron are in a Chlorine ion if there are 17 protons?
The ion Cl-1 has a total of 18 electrons.
How many neutrons are in a Carbon-14 atom if there are 6 protons?
8 neutrons
What is a group in a periodic table?
A vertical column
What is a period in a periodic table?
A horizontal row
What are the group numbers of alkali metals, alkaline metals, halogens, and noble gases?
1, 2, 17 (7A), and 18 (8A)
What is an anion and a cation?
Anion is a negative ion, cation is a positive ion
Do transition metals within the same group show the same chemical properties?
No transition metals do not, but all other elements within certain groups do show similar chemical properties within the group.
How is the periodic table organized?
By number of protons (atomic number).
What is the periodic trend in ionization energy?
Ionization increases left→right across a period and bottom→top up a group. This is due to electrons being held more tightly by the nucleus.
Is the second ionization energy always higher than the first ionization energy, even for group 2 elements?
Yes
What is the periodic trend in electron affinity?
The trend is the same as ionization energy, electron affinity increases left→right across a period and bottom→top up a group. Electron affinity is the energy released when an atom gains an electron.
What is the periodic trend in atomic radius of neutral atoms of elements?
This is the trend opposite to all others. Atomic radius decreases left→right across a period and bottom→top up a group. (This is because the number of energy levels decreases bottom→top up a group and the valence and nuclear charge attractions increase left→right across a period.)
What is the periodic trend in electronegativity?
The trend is the same as ionization energy, electronegativity increases left→right across a period and bottom→top up a group.
What classification of elements is the following?

Boron, Silicon, Germanium, Arsenic, Antimony, and Tellurium
Metalloids
What are some of the physical properties of metals versus nonmetals?
Metals are malleable solids, good conductors of heat and electricity, shiny.

Nonmetals are brittle solids, poor conductors of heat and electricity, dull.
Describe the 2 main intra-molecular bonds
Covalent bonds share electrons while ionic bonds involve the transfer of electrons.

Organic Chemistry

Organic

What is considered the main requirement for a molecule to be classified as organic? Solution
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Hint Unavailable
Must have carbon-carbon, or carbon-hydrogen bonds.

Which of the following molecules is considered organic ? Solution
Only molecules with carbon-carbon, or carbon-hydrogen bonds are considered organic. The following are inorganic molecules: CO2, CO, CN-, H2CO3, CO32-, C22-, etc...

Naming Branched Alkanes

Take note of the 5-ish steps to naming an organic molecule. Use this in your journey ahead... Solution
1) Determine the longest, continuous carbon-chain as the root.

2) Number the chain with the lowest number at the highest priority functional group, and with the lowest combination (sum) of numbers for the side group substituents.

3) Name the priority/parent functional group, and add ending/suffix if applicable. Name the side groups and add prefixes, if any, and place in alphabetical order with the assigned carbon number of each substituent. (Prefixes do not count for alphabetical order: di, tri, tetra).

4) If two of the same substituents exist then number each and include the prefix (di, tri, tetra) in-front of the substituent name.

5) Combine all substituents and the suffix for the carbon chain, including any suffix for alkenes or alkynes.

Naming Branched Alkanes

The name of this molecule is Solution Video
The lowest possible combination of numbers for the substituents is obtained by starting the numbering from the leftmost side of the molecule.

This results in 3, 4, 4 (rather than 4, 4, 5).

Also remember to list the substituents in alphabetical order (e → m → p).

Halogen side groups have a greater priority than alkyl side groups. Therefore start numbering the parent backbone chain from the side closer to the halide group. Solution
Halogen and alkyl side groups have an equal priority. Therefore just start numbering the backbone to give the lowest combination of numbers on side groups.

When naming a molecule with many different side groups, the side groups are listed alphabetically according to the root name of the side group and the prefixes. Solution
When ordering the side groups in the name, the prefixes (mono, di, tri, tetra...) are not considered in the alphabetic ordering.
  • Exception: only the prefixes cyclo-, iso-, and neo are considered for alphabetical order.

Naming Alkanes, Alkenes, Alkynes, and Alkyl Halides

Name the following hydrocarbons.

With lots of branching. Solution
Hint Clear Info
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Hint Unavailable
3-ethyl-2-methyl-4-propylnonane

With multiple double bonds. Solution
Hint Clear Info
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Hint Unavailable
2,4-dimethylpent-1,5-diene

With branching, alkyne, and a halide. Solution
Hint Clear Info
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Hint Unavailable
3-chloro-3-iodobut-1-yne

(Start numbering from the alkyne side)

With equal numbers of carbon in the chain and cyclic. Solution
Hint Clear Info
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Hint Unavailable
The cyclic group takes priority as the backbone when the cyclic carbon number is 'greater than or equal to' the number of carbons in the straight chain.

The straight chain has 4C and the cyclic has 4C, so the backbone is cyclobutane.

sec-butyl cyclobutane

With a longer straight chain than the cyclic group. Solution
Hint Clear Info
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Hint Unavailable
The 8C straight chain takes priority over the 3C cyclic group...

4-cyclopropyl-octane

With more carbons in the cyclic group. Solution
Hint Clear Info
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Hint Unavailable
The longest continuous carbon structure will take priority as the backbone... this is the 6C cyclohexane...

When listing alphabetically, 'cyclo-' counts!

1-cyclobutyl-4-ethyl-cyclohexane

With branching on cyclic. Solution
Hint Clear Info
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Hint Unavailable
3-chloro-1-ethyl-6-methylcyclohexene

(Priority: Alkene > Alkyl > Halogen)

(Lowest numbering combination, must fully encompass double bond at start: 3-1-6 < 2-3-6)

Structural Formula

Draw the structural formula for 4,4-dibromo-2-iodo-5,5-dimethyloctane. Solution Video
Remember in naming that the prefix does not count for alphabetical order (except for iso). The halogen and alkyl side groups have equal priority, so just make the lowest combination of numbers.

Start numbering from the side that will make the lowest combination of numbers of the side groups, from the left-hand side: 2, 4, 4, 5, 5. (Numbering from the right-hand side would be: 4, 4, 5, 5, 7)

Unsaturated Hydrocarbons

What does unsaturated mean? [1] Solution
Hint Clear Info
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Hint Unavailable
Unsaturated means it has double or triple bonds

Physical Properties of Hydrocarbons

At room temperature, propane is a gas, octane is a liquid, and a 20-carbon hydrocarbon is a solid. Solution
Melting point and boiling point of hydrocarbons increase with molecular weight. C1-C4 is gas, C5-C12 is liquid, and C20+ is solid.

Order the following hydrocarbons in order of decreasing boiling point from top to bottom. Solution
Pentane
Decane
Ethane
Hexane
The 2 factors that affect boiling point: molecular weight, and intermolecular forces.

When the functional groups are the same, then the molecular weight is what determines the boiling point. Higher molecular weights have higher boiling points, and visa versa.

Butane has a lower boiling point than 2-methylpropane. Solution
Comparing the molecular weights first, they are roughly the same so we look at the branching next. Butane has a higher boiling point than 2-methylpropane because it packs more tightly. Branched molecules of a similar molecular weight will have a lower boiling point.

Choose the most correct statement. Solution
  • Butane has a lower solubility in water than Methane
  • Ethane is slightly soluble in water (over 50mg/L at standard conditions)
  • Hydrocarbons with less than 3 carbons have a low solubility in water -- yes, the are slightly soluble in water.
  • Low-carbon compounds (1-3) carbons are slightly soluble in water and solubility decreases as carbon number of the hydrocarbon increases.

Addition Reactions of Acid Halides with Alkenes (Markovnikov)

2-methyl-1-butene reacts with HBr to form what major product? Solution Video
Markovnikov Addition
In the major product, the hydrogen (H) atom attaches to the carbon with fewer alkyl (C) substituents, or the larger number of hydrogen atoms. The halide (X) group becomes attached to the carbon with more alkyl substituents.

The bromine attaches to the 3˚ carbon and the hydrogen attaches to the 1˚ carbon across the double bond. The major product is 2-bromo-2-methylbutane (and the minor product is 1-bromo-2-methylbutane).

What reaction type results in the major product of the reaction shown below? Solution
Markovnikov Addition in Hydrohalogenation
In the major product, the hydrogen (H) atom attaches to the carbon with fewer alkyl (C) substituents, or the larger number of hydrogen atoms. The halide (X) group becomes attached to the carbon with more alkyl substituents.

Adding water to which of the following will make an equal mixture of two different products? Solution Video
Markovnikov Addition
In the major product, the hydrogen (H) atom attaches to the carbon with fewer alkyl (C) substituents, or the larger number of hydrogen atoms. The hydroxide (OH) group becomes attached to the carbon with more alkyl substituents.

2-methyl-2-butene
  • Major product will form with -OH group attached to carbon 2, forming 2-methyl-2-butanol
  • OH will add to the 3˚ carbon more than the 2˚ carbon
  • (Minor product formed is 3-methyl-2-butanol)
Ethene (Ethylene)
  • Ethene is symmetrical about double bond, therefore will form 100% same molecule (highest yield)
  • OH group adds to either of the 1˚ carbons across double bond
  • Forms ethanol
2-pentene
  • Both carbons are 2˚, therefore there will be equal amounts of the two different products in a 50-50% mix of: 3-pentanol and 2-pentanol
  • (The minor product on one is the major product of the other so it is only 50-50)

Similar to alkenes, addition of acid halides to alkynes follows Markovnikov's rule. Solution
The halogen bonds to the more highly substituted carbon... And in the presence of excess acid halide, a further addition reaction will occur to the alkene to produce a di-halide carbon.

Structural (Constitutional) Isomers

Draw three structural (constitutional) isomers of hexane C6H14. Solution Video
Draw any three of: hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylpentane, 2,2-dimethylpentane

Isomers

Isomers must always have the same chemical formula. Solution
All isomers have the same chemical formula, but either the bonding or the spatial arrangement is/are different.

Two isomers have the same bonding, but different arrangements in across carbon-carbon double bonds. Determine the classification of isomer. Solution
Constitutional/Structural Isomers
Different bonding

Stereoisomers Isomers
Same bonding, dfferent arrangement... Eg)
  • Geometric Diastereomers (different arrangement across C=C bonds)
  • Enantiomers (mirror image, non-superimposable)
CC: Yassine Mrabet, 2008

Types of Isomers (Chart in Answer)

Classify the types of isomers below.

Alkenes... Solution Video
cis-2-Butene and trans-2-Butene are geometric (cis-trans) isomers, which are under the category of diastereomer and stereoisomer.
CC: Yassine Mrabet, 2008

Branched alkanes... Solution Video
Conformational isomers are a type of stereoisomer in which the bonding groups differ by rotation around a single C-C bond.
CC: Yassine Mrabet, 2008

Cyclic molecules... Solution Video
These cyclic ether molecules are structural isomers (aka constitutional isomers) because they would have the same chemical formula (C3H6O3), but they have a different bond structure.
CC: Yassine Mrabet, 2008

Cyclic, with side groups... Solution
These diols (molecules containing two hydroxyl groups) are conformational isomers because the hydoxy group is rotated or flipped-up around a chiral carbon.

These are not enantiomers because they are not non-superimposable mirror images.
CC: Yassine Mrabet, 2008
(Not a diastereomer because does not have double bonds)

(Not constitutional/structural because carbons still have same things bonded to them)

Chirality: Enantiomers

What are the main requirements for molecules to be considered enantiomers? [2] Solution Video
Hint Clear Info
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Hint Unavailable
Enantiomers are molecules that have chiral centers, and are non-superimposable mirror images.

2-bromo-2-methylbutane exhibits chirality. Solution Video
False because the molecule doesn't have 4 different substituents, rather it has 2 methyl groups around the central carbon atom. The substituents are: Bromine, Ethane, Methyl, and Methyl.

Stereoisomers

Two stereoisomers are shown below. Determine the carbon number of the chiral center. Solution
carbon #
Hint Clear Info
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Hint Unavailable
Carbon number 3 has four different groups on each bond, therefore it is a chiral center.

Chiral Centers (Stereocenters)

How many stereoisomers are possible with 3 chiral centers in a molecule? Solution
Hint Clear Info
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Hint Unavailable

The number of chiral centers in this Cholesterol molecule is Solution
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Hint Unavailable
Chiral centers have different groups on all 4 bonds around a carbon. (Remember that chiral carbons are asymmetric such that the mirror image is non-superimposable.)

Naming Alcohols

Name the following alcohols using IUPAC naming.

Which of the following synonyms is the correct IUPAC name? Solution
IUPAC naming places the number next to the parent/functional group suffix... butan-2-ol Remember to always drop the last "e" from the hydrocarbon name.

With one alcohol... Solution
Hint Clear Info
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Hint Unavailable
2-methyl-pentan-2-ol

With two alcohols... Solution
Hint Clear Info
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Hint Unavailable
2-methyl-pentan-2,3-diol

With three alcohols... Solution
Hint Clear Info
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Hint Unavailable
2-methyl-hexan-2,4,5-triol

Cyclic with two hydroxide groups Solution
Hint Clear Info
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Hint Unavailable
cyclopropan-1,2-diol

Cyclic with three hydroxide groups, and more... Solution
Hint Clear Info
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Hint Unavailable
Priority: alcohol > alkene > alkyl Steps:
  1. Find the longest continuous carbon chain
  2. Start numbering from the side with the highest priority functional group
  3. Number the side groups with the lowest combination of numbers
  4. Add carbon numbers, prefixes, and drop the 'e' from root name.
  5. Order alphabetically
4-methyl-cyclohex-1-en-1,3,5-triol

Naming Alcohols

The following name is incorrect. Determine the correct name. Solution 1-methyl-cyclohexane-3-ol
Hint Clear Info
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Hint Unavailable
The alcohol takes priority so you should start numbering from the side with the alcohol... Also you should drop the 'e' at the end of the root name. 3-methyl-cyclohexan-1-ol

Name the following saturated, branched alcohol molecule. Solution
Hint Clear Info
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Hint Unavailable
Steps...
  1. Find the longest continuous carbon chain
  2. Start numbering from the side with the highest priority functional group
  3. Number the side groups with the lowest combination of numbers
  4. Add carbon numbers, prefixes, and drop the 'e' from root name.
  5. Order alphabetically
4,7-diethyl-3,7-dimethyl-decan-2-ol

Name the following unsaturated alcohol molecule. Solution
Hint Clear Info
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The alcohol has the highest priority, so start numbering from that end... 3,7-dimethyl-oct-6-en-1-ol

Terminology of Alcohols

Determine whether the following molecules are primary, secondary, or tertiary...

This ethanol (alcohol) molecule. Solution
Primary, 1˚ because the carbon attached to the hydroxide group is attached to 1 other carbon.

This branched alcohol. Solution
Tertiary, 3˚ because the carbon attached to the hydroxide group is attached to three other carbons.

This cyclic (cyclohexan-1-ol) alcohol. Solution
Secondary, 2˚ because the carbon attached to the hydroxide group is attached to two other carbons.

Physical Properties: Melting & Boiling Points of Alcohols

Alcohols are composed of a non-polar, hydrophobic alkyl group (CXHY), and a polar, hydrophilic hydroxide group (OH). The electrostatic dipole in the hydroxide group allows the non-polar chain to dissolve in water.

CXHYOH

Melting and boiling point of alcohols depends on what two main factors? [2] Solution
Hint Clear Info
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Molecular weight and side group branching.

Which of the following alcohols has the highest boiling point? Solution
Because it can form the most hydrogen bonds, which makes the intermolecular force strong and increases the boiling point (the point at which intermolecular forces are overcome in the liquid phase to spread apart into the gas phase).

Reaction: Hydration of Alkene Produces Alcohol

Hydration of propene mainly produces Solution Video
Markovnikov's Rule
The hydrogen (H) attaches to the carbon atom with the most hydrogens, while the hydroxide (OH) attaches to the carbon with the highest alkyl substitution

Reactions: Addition (Hydration) Reactions

Complete the reaction (draw in your notes) and name the product formed. Solution Video
Hint Clear Info
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Hint Unavailable
Markovnikov's Rule
The hydrogen (H) attaches to the carbon atom with the most hydrogens, while the hydroxide (OH) attaches to the carbon with the highest alkyl substitution.



3-methyl-hexan-3-ol

Reaction: Elimination (Dehydration) of Alcohol

Treating an alcohol with concentrated sulfuric acid (H2SO4) produces the following molecule. What would the starting molecule have been? Solution Video
The concentrated sulfuric acid (H2SO4) catalyzes the dehydration of the alcohol in the starting molecule.

A hydrogen (H) and a neighboring hydroxyl (OH) group is then removed, resulting in the formation of a double bond (C=C).

Answer choice 'C' is incorrect because the dehydration of this alcohol would yield a major product with an internal double bond on more highly substituted carbons.

Reactions: Combustion of Alcohols

Complete combustion of one mole of 3-ethyl-2-methylhexan-1-ol would yield how many moles of carbon dioxide?
Solution Video
Hint Clear Info
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mol
Hint Unavailable
The moles of carbon dioxide equals the number of carbons in one mole of the alcohol molecule.

CxHYOZ + mO2 --> xCO2 + nH2O

Naming Aldehydes

The name of the following molecule is Solution Video
Hint Clear Info
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Recognize the aldehyde functional group; aldehydes take the suffix -al
The backbone is 5 carbons long, so it takes the root name pentan-... = pentanal.

Naming Aldehydes

Name the following molecules

Solution
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4-methylpentanal
Start numbering from the higher priority functional group - the aldehyde.

Solution
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Hint Unavailable
5-bromo-7-hydroxy-4-methylheptanal
Start numbering from the higher priority functional group - the aldehyde.

Physical Properties of Aldehydes

Propanal has a lower boiling point than butane. Solution
Propanal has a higher boiling point than butane. Due to: higher polarity and dipole-dipole interaction in the aldehyde.

Which of the following compounds has the lowest boiling point? Solution
Between equivalent aldehydes and alcohols, like hexanal and hexanal, the aldehyde will always have the lower boiling point. Aldehydes cannot hydrogen bond!

Of course, molecules with lower molecular weights have lower boiling points (between hexanal and octanal).

Structural Isomers: Aldehyde

Which of the following is a structural isomer of 1-propanal? Solution
Structural isomers (aka constitutional isomers) have the same chemical formula, but have different bond connectivity in their structures.

1-propanal is an aldehyde, and aldehydes have structural isomers with ketones (with same chemical formula).

Reactions: Oxidation of Alcohols

In the presence of a strong oxidizing agent, propan-1-ol is fully oxidized into propanal as the end product. Solution
A strong oxidizing agent will not stop at propanal, and will continue oxidation to form propanoic acid.

(To make aldehydes, a primary alcohol must be oxidized with a weak oxidizer like PCC).

Reactions of Aldehydes

Determine the name of the product of the following reaction. Solution
Hint Clear Info
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Hydrogenation of an aldehyde will reduce it to an alcohol
Hydrogenation of an aldehyde will reduce it to an alcohol... propanol

Naming Ketones

Name the following ketone molecules.

Solution
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Accept butanone (or 2-butanone), when the molecule is superimposable when rotated in 3D space, you don't have to indicate the carbon number. There is no other possible position for the internal carbonyl carbon in a butane chain.

Solution
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4-methyl-2-pentanone

Start numbering from the end with the higher priority functional group - the ketone.

Solution
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3-methyl-2,6-heptdione

Start numbering from the end with the higher priority functional group - the ketone.

Structural (Constitutional) Isomers of Ketones

Ketones have structural (constitutional) isomers that are aldehydes. Solution
As long as it has the same molecular formula.

Draw a structural (constitutional) isomer of 3-methylpentanal. Solution
Draw any ketone or aldehyde, with the same molecular formula. (not shown)

4-methyl-2-pentanone and 3-methylpentanal are structural isomers. Solution
These two ketone and aldehyde molecules have the same molecular formula: C6H12O.

Properties of Ketones

Ketones have boiling points slightly higher than aldehydes of the same carbon chain length. Solution
The molecular weight of ketones is slightly higher than that of aldehydes.

Reactions of Ketones: Oxidation of Alcohols

Oxidation of the following molecule will yield which product (if any)? Solution
Tertiary (3˚ alcohols) do not react in oxidation reactions since further oxidation from the alcohol would make a double bond, and there is no space for additional bonds on the central carbon atom.

A tertiary alcohol is oxidized to form a ketone in the presence of potassium permanganate (KMnO4). Solution
Although potassium permanganate (KMnO4) is a very strong oxidizer, 3˚ alcohols cannot be oxidized to produce a ketone group. Only 1˚ and 2˚ alcohols can do this, although oxidation of 1˚ alcohols form aldehydes or carboxylic acids rather than ketones.

Terminology of Carboxylic Acids

The standard name of the -COOH group in the diagram below is: Solution
Hint Clear Info
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The -COOH group is a carboxyl. (The -C=O group is a carbonyl).

Naming Carboxylic Acids

Name the following carboxylic acid molecules.

With a halide... Solution
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4-bromopentanoic acid

With lots of branching... Solution
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2-ethyl-3,5-dimethylheptanoic acid

With two carboxyl groups... Solution
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butandioic acid

(Notes: drop the 'e' and don't have to indicate 1,4 because carboxylic acids have to be terminal.)

Properties of Carboxylic Acids

Order the following molecules in order of decreasing boiling point from top to bottom. Solution
Pentanal
Pentane
Pentanol
Pentanoic acid
If the molecular weights are all the same then...

The boiling point is based on the strength of the primary intermolecular force: hydrogen bonds are strongest, then dipole-dipole, then London dispersion.

Carboxylic acids have hydroxide groups (-OH) that have the strongest hydrogen bonding.
Alcohols have hydroxide groups (-OH) that hydrogen bond, but are less strong than the ones in carboxylic acids.
Amines have amino groups (-NH) that hydrogen bond, but are even weaker than alcohols.
Alkanes have very weak London dispersion intermolecular forces.
The boiling and melting points from high to low:
carboxylic acid → alcohol → aldehyde → alkane

Reactions of Carboxylic Acids

Oxidation of which molecule will produce the following carboxylic acid? Solution
Oxidation of alcohols with a strong oxidizing agent like potassium permanganate (KMnO4) will make carboxylic acids.

Naming Esters

Name the following ester molecules.

With an alkane chain on the oxygen... Solution
Hint Clear Info
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Hint Unavailable
butyl methanoate


With an alkane chain on the carbonyl carbon... Solution
Hint Clear Info
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methyl pentanoate


With chains all over... Solution
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3-pentyl 2-ethylbutanoate

Naming Esters

Name the following ester molecule. Solution
Hint Clear Info
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Hint Unavailable
3-chlorobutan-1-ol 4-bromo-3-methylbutanoate


Properties of Esters

Different ester molecules have a wide range of characteristic odours. Smells are detected by olfactory receptors in the nose when an ester molecule lands on one of the receptors. Which molecule would have the strongest smell at room temperature? Solution
To detect the smell, the ester molecule must be evaporated into the air as a gas. The molecule that evaporates most will have a relatively low boiling point; with a lower molecular weight. The long chain molecules will not vaporize at room temperature and not be easily detected.

Ester Reactions: Esterification

In the presence of heat and an acid, ethanol + acetic acid will produce an ester with four carbons. Solution
Ethanol + Acetic Acid --> Ethylacetate

Ester Reactions: Synthesis of Esters

Esters are formed in a condensation reaction when hydrogen (-H) from a carboxylic acid and a hydroxyl (-OH) group from alcohol combine to form a water molecule, in the presence of heat. Solution
Esters are formed when the hydroxyl (-OH) from a carboxylic acid and a hydrogen (-H) from alcohol combine to form a water molecule, in the presence of heat.

State the reactants required to synthesize the following molecule and provide the name for this Ester. Solution
Alcohol + Carboxylic acid → Ester

(This is a dehydration reaction)

Ester Reactions: Hydrolysis

Sodium hydroxide is added to a propylmethanoate ester, shown below. Determine (in your notes) the molecular structure of the conjugate base and conjugated acid products. Solution

The following process is called... Solution
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The ester bonds in triglycerides (fats, lipids) are cleaved with the base (NaOH), which creates an alcohol (glycerol) and a carboxylate anion salt with the sodium. This is basically how soap is made... saponification

Naming Ethers

Name the following ether. Solution CH3CH2CH2CH2CH2-O-CH2CH2CH2CH3
Hint Clear Info
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Hint Unavailable
Take the longest carbon chain (-pentane) and that is the backbone. Then add the other chain on the oxygen (but-) as the prefix...

butoxypentane

Properties of Ethers

The boiling point of butane is higher than the boiling point of ethoxyethane (diethyl ether). Solution
The boiling point of butane is lower than the boiling point of ethoxyethane (diethyl ether). This is due to the polarity of the C-O bonds in ethers being higher than the polarity of C-C bonds in the alkane, resulting in greater intermolecular forces and an increase in boiling point.

Reactions: Ether Dehydration Reaction

Fill in the missing reactant, X, for the following condensation reaction. Solution
This is a condensation reaction between a hydroxyl, OH group from one alcohol and a hydrogen, H from another alcohol.

Terminology of Amines

Match the molecule with the correct classification. Solution
Primary (1˚)
Secondary (2˚)
Tertiary (3˚)
Quaternary (4˚)
Both amine molecules are primary (1˚) because the nitrogen is attached to 1 carbon.

The following molecule is classified as: Solution
Secondary (2˚) amines are bonded to 2 carbons. (1˚ amines are bonded to 1 carbon, and 3˚ amines are bonded to 3 carbons).

Naming Amines

Name the following molecule with IUPAC nomenclature. Solution
Hint Clear Info
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Hint Unavailable
N-ethyl-N-methylaminopropane The highest carbon chain gets the root name, while the remaining substituents are numbered with N and listed in alphabetical order. (Sometimes can be named with non-Iupac: ethylmethylpropylamine, or when CA naming convention: N-ethyl-N-methylpropanamine)

Naming Amines

Name the following amine molecules.

Solution
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N-ethyl-2-aminobutane
(or with CA naming convention: N-ethyl-2-butanamine)

Solution
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1,3-diaminopropane
(or with CA naming convention: 1,3-propanediamine)

Solution
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Hint Unavailable
N-ethyl-N-methylaminoethane
(or with CA naming convention: N-ethyl-N-methyl-1-ethanamine)

Solution
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Hint Unavailable
2-amino-3-methylhexane
(or with CA naming convention: 3-methyl-2-hexanamine)

Solution Video
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Hint Unavailable
The ethyl group on the amine (N-ethyl) gets named first. The longest carbon-chain backbone is 10 carbons, decane... N-ethyl-5-amino-2,9-dimethyl-5-propyldecane (or CA naming convention: N-ethyl-2,9-dimethyl-5-propyl-5-decylamine)

Naming Amines

Two lab partners are trying to name an amine product but they are in a disagreement over the correct IUPAC name. Determine who is correct.

Sydney wants to name it 2-chloro-4-aminoheptane, but Caroline wants to name it 4-amino-2-chloroheptane. Solution
Caroline has the correct name: 4-amino-2-chloroheptane (Also acceptable would be the CA naming convention for amines: 2-chloro-4-heptanamine)

Jukka wants to name it 3-amino-2-bromo-N-methyl-1-hexene, but Koji wants to name it N-methyl-3-amino-2-bromo-1-hexene. Solution
Koji has the correct name: N-methyl-3-amino-2-bromo-1-hexene (In this example we would not use the -amine naming convention according to CA rules because the double bond has priority in the naming system).

Properties of Amines

All pure primary, secondary, and tertiary amines can hydrogen-bond. Solution
Only primary and secondary amines have N-H bonds that can hydrogen bond. The N-C bonds in tertiary amines cannot hydrogen bond.

Properties of Amines

Order the following molecules in order of increasing boiling point (from bottom to top) by dragging them. Solution Video
Hexanol
Hexanamine
Hexane
Hexanoic acid
Hexanoic acid has the strongest hydrogen bonding and highest molecular weight, so it has the highest boiling point. Hexanol can hydrogen bond. Hexanamine can hydrogen bond but has a lower boiling point than hexanol because the N-H dipole is weaker than the O-H dipole in the alcohol.

Reactions of Amines with Alkyl Halides

Draw and name the products (if any) of the following reactions between an amine and alkyl halide.

Solution
There is no reaction. A tertiary (3˚) amine will not react because there is no hydrogen on the Nitrogen atom.

Solution
= N-ethyl-N-propyl-2-aminopentane + Hydrogen bromide

Solution
= N-Ethylpropanamine + Hydrogen chloride (or N-ethylaminopropane, or N-Ethylpropylamine)

Functional Groups

Name the following functional group. Solution
Hint Clear Info
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Hint Unavailable
You should recognize the functional group, amide.

Naming Amides

Name the following amide molecules.

Solution Video
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Hint Unavailable
N-ethyl butanamide

Solution
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N,N-diethyl ethanamide

Solution Video
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N,N-diethyl-3-methylpentanamide

Physical Properties of Amides

N-propyl-3-methyl butanamide can hydrogen bond. Solution
The N-H bond in the amide is capable of hydrogen bonding.

Amide Condensation Reactions

Which of the following molecules cannot react with ethanoic acid in a condensation reaction? Solution
Tertiary (3˚) amines like N,N-dimethylaminopropane cannot react in a condensation reaction with ethanoic acid because this reaction requires at least one N-H bond. All the other amines listed can react.

Synthesizing Amides

N,N-dimethyl butanamide can be synthesized from Solution Video
Draw the N,N-dimethyl butanamide amide molecule first to visualize the bonding.

To form the amide bond (C-N), there must have been a condensation (dehydration) reaction between a secondary (2˚) amine and carboxylic acid. N,N-dimethyl butanamide

Reactions of Amides

Complete the following reactions and name the products.

[Hydrolysis] Solution Video
N-ethyl propanamide + water → propanoic acid + 1-amino ethane (ethylamine)


[Condensation] Solution Video
3-methyl-butanoic acid + N-methyl-1-amino ethane → N-ethyl-N,3-dimethyl propanamide + water


Amides

Protein molecules can be split by adding water, separating into amino acids. Solution
Protein molecules are polypeptide chains (polymers) joined together with amide bonds. These amide bonds can be hydrolyzed, broken with water.

Carbonyl Groups

Carbonyl (-C=O) groups are present in all of the following molecules: Solution Ester, Ketone, Amide, Carboxylic Acid, Aldehyde
Carbonyl groups are carbon atoms that are double-bonded to oxygen.

Naming Simple Aromatic Hydrocarbons

The common name for this aromatic molecule is: Solution
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...phenol (this is a benzene ring with one alcohol side group)

Benzene Structures

What is ortho, meta, and para and when are they used? [1] Solution
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The ortho, meta, and para naming system is an alternative system that is used when benzene rings are substituted with exactly 2 side groups. This naming system cannot be used when benzene has 1 or 3+ side groups.

Ortho side groups are on adjacent carbons. Meta side groups are on carbons that have one carbon between them. Para side groups are on carbons with two other carbons between them. Ortho Meta Para

Solution
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1-ethyl-3-methylbenzene

(aka m-methyl ethyl benzene) -- the ortho/meta/para nomenclature is interchangeable with the other naming system, but can only be used with two side groups. The other system can be used with two or more side groups.

Solution
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4-methyl-1-propylbenzene

The higher molecular weight propyl takes priority over methyl.

The substituents should be in alphabetical order with 'm' before 'p'. So 1-propyl-4-methylbenzene is not entirely correct.

(aka p-methyl propyl benzene) -- the ortho/meta/para nomenclature is interchangeable with the other naming system, but can only be used with two side groups. The other system can be used with two or more side groups.

Aromatic Hydrocarbons: Alyklbenzene

Name the following, which have benzene as a substituent.

Solution
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Hint Unavailable
4-methyl-2-phenyl-1-hexene.

(Benzene becomes phenyl as a side group).

The substituents should be in alphabetical order with 'm' before 'p'.

Solution
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Hint Unavailable
4-ethyl-5-methyl-3-phenyl-1,8-octadiene



Reactions of Aromatics

Given a simple benzene molecule as the reactant, what happens when it is reacted with...

Excess Cl2 (g) in the presence of AlCl3 at room temperature? Solution
At room temperature (and at regular pressure) the benzene ring maintains aromaticity (the double bond arrangement) and is substituted by one halogen.

Excess Cl2 (g) in the presence of AlCl3 with heat (∆) at 300˚C and UV light (hv)? Solution
See the benzene ring loses aromaticity to become a substituted cyclohexane.

Excess H2 (g) in the presence of heat (∆) and Platinum (Pt) or Nickel (Ni) catalysts. Solution
Hydrogenation removes the aromaticity of the benzene ring to form cyclohexane.

The alkyl halide, chloroethane in the presence of AlCl3. Solution
Friedel-Crafts actylation adds the alkyl group attached to the chlorine to the benzene ring. The byproduct is hydrochloric acid where the hydrogen is from the benzene ring and the chlorine is from the alkyl halide substrate.

Reactions of Aromatics

Determine the product when phenylmethanol is oxidized in a controlled oxidation. Solution
The controlled oxidation of phenylmethanol will produce benzaldehyde...

Polymers

Polymers are made of identical monomer subunits. Solution
It is true that polymers are made of many monomer subunits, but the monomer subunits do not have to be identical when joined by addition or condensation polymerization.

Which one of the following common molecules is not a polymer? Solution
Glucose is not a polymer because it is a monomer! Glucose is a monosaccharide like the monomers that make polysaccharide polymers like starch or cellulose...

Examples of polymers...
  • Polysaccharides (starch, cellulose...)
  • Deoxyribonucleic Acid (DNA)
  • Synthetic polymers (like Nylon, Teflon, Polyeser...)
  • Proteins
  • Rubber (vulcanized)

Carbohydrates and Amino Acids

Carbohydrates and amino acids are polymers. Solution
Amino acids are monomers, the polymer of amino acids is a protein (polypeptide).

Amino Acid Polymerization

Fill in the blank: Polymerization of amino acids through a _____________ reaction creates a bond between ______________ atoms. Solution

Polysaccharides

Sucrose is a polysaccharide made from the monosaccharide subunits Solution
Polysaccharides are polymers of simple sugar molecules. In this case, Sucrose is a polysaccharide made from Glucose and Fructose.

Polymerization

The condensation reaction to polymerize the following molecules will form what monomer subunit? Solution Video
A carboxylic acid on one molecule and an alcohol on another molecule condense (dehydrate) to form the ester linkage (...CH2OOCCH2...) plus a water molecule H-OH. = [—OCH2CH2OOCCH2CH2CO—]n

Polymerization of Alkenes

Draw the monomer subunit when 3-bromo-5-methyl-1,6-heptadiene undergoes polymerization Solution

Draw (in your own notes) and name the monomer subunit in the following polymer. Solution
Hint Clear Info
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Hint Unavailable
The monomer subunit is... BUT, it's considered best form to name the monomer before it polymerizes... 1-bromo-2-chloro-ethene (not 1-bromo-2-chloro-ethane)

Polymerization of Carboxylic Acids and Amines

Draw the monomer subunit that forms when a di-carboxylic acid, butanedioic acid undergoes polymerization with a di-amine, N,N-dimethyl-1,3-diaminopropane. Solution Video
This condensation reaction (dehydration of a water molecule) will create an amide bond. The monomer subunit contains one of each 'type' of molecule and shows the repeating unit as if it had undergone the polymerization (condensation in this case) reactions on both ends of the monomer subunit molecule.

Other: Free Radical Mechanism

The steps shown in the following chain mechanism of free radicals is called Solution
In these steps you can see the free radical propagating through to the next molecules in a chain reaction.

Naming Functional Groups

Name all of the functional groups present in this molecule. [5] Solution
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Hint Unavailable
Benzene, Amine, Amide, Alkene, Ether

Priority of Naming with Multiple Functional Groups

Name the following molecule given the priority table below. Solution
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Priority RankingFunctional Group
1 (Highest Priority)Carboxylic acid
2Ester
3Amide
4Aldehyde
5Ketone
6Alcohol
7Amine
8Ether
9Alkene
10Alkyne
11Halide
12 (Lowest Priority)Alkane branch
5-amino-3-hydroxy-oct-7-enoic acid


Carboxylic acids rank highest on the list. Start numbering from the carbonyl carbon on the carboxylic acid functional group.

Synthesis

Determine the structure of each unknown molecule in the pathways below.

The two possible molecules that would make the given alcohol in the reactions below. Solution

The molecules along the pathway to form the ester. Solution

Starting with an alkene. Solution

Starting with an alkene and ending with an amide. Solution

Flashcards: Organic Chemistry

What is the prefix of an alkane with 1 carbon?
meth
What is the prefix of an alkane with 2 carbons?
eth
What is the prefix of an alkane with 3 carbons?
prop
What is the prefix of an alkane with 4 carbons?
but
What is the prefix of an alkane with 5 carbons?
pent
What is the prefix of an alkane with 6 carbons?
hex
What is the prefix of an alkane with 7 carbons?
hept
What is the prefix of an alkane with 8 carbons?
oct
What is the prefix of an alkane with 9 carbons?
non
What is the prefix of an alkane with 10 carbons?
dec
Name:

2,4-dimethylpenta-1,5-diene
Name:

3-chloro-1-ethyl-6-methylcyclohexene
Which of the following functional groups is the highest priority, receiving the lower number in the molecule name?

Alkyne, Ester, Alcohol
The Ester is the highest priority.

Order:
Carboxylic acid → Ester → Amide → Aldehyde → Ketone → Alcohol → Amine → Ether → Alkene → Alkyne → Alkyl halide
What is the functional group in CH3COOH?
COOH is a carboxylic acid
What are the prefix and suffix for an alcohol?
Prefix: hydroxy-
Suffix: -ol
What are the prefix and suffix for a ketone
Prefix: oxo-
Suffix: -one
What are the prefix and suffix for an aldehyde?
Prefix: oxo-
Suffix: -al
What are the prefix and suffix for a carboxylic acid?
Prefix: carboxy-
Suffix: -oic acid
What is the suffix for an ester?
-oate
What is the suffix for an ether?
-ether
What is the suffix for an amide?
-amide
What are the prefix and suffix for an amine?
Prefix: amino-
Suffix: -amine
Name:

2-methyl-pentan-2-ol
Name:

2-methyl-pentane-2,3-diol
Name:

4-methylpentanal
Name:

5-bromo-7-hydroxy-4-methylheptanal
Name:

4-methyl-2-pentanone
Name:

3-methyl-2,6-heptadione
Name:

4-bromopentanoic acid
Name:

butyl methanoate
Name:

methyl pentanoate
Name:

CH3CH2CH2CH2CH2-O-CH2CH2CH2CH3
butoxypentane
Name:

N-ethyl-N-methylpropanamine
Name:

N-ethyl-2-aminobutane
Name the functional group:

Amide
Name:

N-ethyl butanamide
Name:

N,N,3-triethyl butanamide
Name:

1-ethyl-3-methylbenzene
Name:

4-methyl-2-phenyl-1-hexene
What is a constitutional isomer?
A constitutional (or structural) isomer has different connectivity of atoms with the same chemical formula
What is the difference between a constitutional isomer and a sterioisomer?
While the chemical formula of each isomers remains the same, constitutional isomers have different connectivity of atoms while stereoisomers have the same connectivity but different spatial arrangement.
Are all of the following considered stereoisomers?

Conformation isomer, enantiomer, and diastereomer
Yes.

(Diastereomers are cis-trans, conformational isomers are anti/eclipse/gauche, and enantiomers are R/S)
What type of isomers?

Geometric/Diastereomers (of the Stereoisomer category)
What type of isomers exhibit chirality?
Enantiomers

(Chiral isomers have the same connectivity, but are non-superimposable mirror images because of the different spatial arrangement of atoms)
How many chiral centers are in this molecule?
8!
Can ketones and aldehydes form structural isomers?
Yes

For example C3H6O could be either a ketone (propan-2-one) or an aldehyde (propanal)
Describe the trend in boiling and melting point in the molecular weight of straight chain hydrocarbons
Melting point and boiling point of hydrocarbons increase with molecular weight. C1-C4 is gas, C5-C12 is liquid, and C20+ is solid.
Describe the trend in boiling and melting point in branched hydrocarbons (of the same molecular weight)
Melting point and boiling point of hydrocarbons decreases with more branching
What is a tertiary (3˚) carbon?
A carbon that is bonded to three other carbons. (There are also 1˚, 2˚, and 4˚)
Compare the melting point and boiling point of cis-2-Butene and trans-2-Butene
cis-2-Butene has a higher boiling point (because of the higher polarity in the molecule, they hold tighter intermolecular forces in liquid)

trans-2-Butene has a higher melting point (because of the shape they pack tighter in a solid)
Describe the major product of Markovnikov addition of an acid halide to an alkene
In the major product, the hydrogen (H) atom attaches to the carbon with fewer alkyl (C) substituents, or the larger number of hydrogen atoms. The halide (X) group becomes attached to the carbon with more alkyl substituents.
Would the addition of excess chlorine (Cl2) to an alkyne produce a substituted alkane or alkene?
Substituted alkene
Reduction of an alkyne to an alkane is completed through what type of reaction?
Hydrogenation
Addition of water to an alkene results in what type of functional group?
Alcohol
How does the hydroxyl (-OH) group affect the boiling point of alcohols?
Hydrogen bonding increases the intermolecular forces, requiring greater energy to pull apart during vaporization/evaporation.
Hydration of a straight-chain alkene produces what type of alcohol?
Secondary (2˚) alcohol

E.g.) propan-2-ol
Adding concentrated sulfuric acid (H2SO4) to an alcohol produces what?
A double bond (alkene).
Which reducing agent is strong enough to reduce a carboxylic acid into an alcohol?

Sodium tetrahydridoborate, NaBH4

Lithium tetrahydridoaluminate, LiAlH4
Lithium tetrahydridoaluminate, LiAlH4

(NaBH4 is too weak an can only reduce aldehydes).
Treating butanoic acid with LiAlH4 would produce what molecule?
butanol
Adding an acid halide to an alcohol produces what?
alkyl halide
Adding PCC to a primary (1˚) alcohol produces what?
An aldehyde

(PCC is a weak-ish oxidizer)
What is the major product when concentrated sulfuric acid (H2SO4) is added to a primary 1˚) alcohol?
An internal alkene

(the minor product is a terminal alkene)
What is the product when water is added to 1-chloropropane?
propanol

(A hydroxyl from the water replaces the halogen, with a byproduct HCl)
Can aldehyde functional groups hydrogen-bond amongst themselves?
No. (Hydrogen bonding requires a hydrogen bonded to a highly electronegative atom like N, O, or F)
How does the boiling point of an aldehyde compare to an alkene of a similar molecular weight?
The boiling point of the aldehyde is higher because of the polarity in the carbonyl carbon, resulting in dipole-dipole intermolecular interactions.
What has a lower boiling point?

Octanal or Octanol
The Octanal aldehyde has a lower boiling point than the alcohol because aldehydes cannot form hydrogen bonds
What is the weaker oxidizing agent that will oxidize a primary (1˚) alcohol into an aldehyde and not a carboxylic acid?
PCC
Reacting an aldehyde with hydrogen in the presence of a catalyst, heat, and pressure will produce what type of molecule?
A primary (1˚) alcohol
Can ketone functional groups hydrogen-bond amongst themselves?
No. (Hydrogen bonding requires a hydrogen bonded to a highly electronegative atom like N, O, or F)
Oxidation of what type of molecule with potassium dichromate (K2Cr2O7) produces a ketone?
A secondary (2˚) alcohol
Explain why this molecule cannot be oxidized

Tertiary (3˚) alcohols be oxidized to produce a ketones since oxidation from the alcohol would make a double bond, and there is no space for additional bonds on the central carbon atom.
Treating a ketone with a reducing agent (like LAH or NaBH4) produces what type of molecule?
A secondary (2˚) alcohol
Hydrogenation of a ketone with Hg and an acid produces what type of molecule?
An alkane
Treating a carboxylic acid with a reducing agent (LAH) produces what type of molecule?
Alcohol
Treating an aldehyde or 1˚ alcohol with KMnO4 will make what type of molecule?
Carboxylic acid
How does the boiling point of a carboxylic acid compare to an aldehyde (of a similar molecular weight)?
Carboxylic acid has a higher b.p.
How does the boiling point of a carboxylic acid compare to an alcohol (of a similar molecular weight)?
Carboxylic acid has a higher b.p.
What is the proper name of acetic acid?
This carboxylic acid (CH3COOH) is called ethanoic acid
What is one of the main sensory characteristics of esters?
Smell

(Different ester molecules have a wide range of characteristic odours.)
Reduction of an ester with LAH produces what type of molecule?
A primary alcohol
What does the following combination produce?

Ethanol + Butanoic Acid
Ester

Ethyl butanoate
What is the general type of reaction between Ethanol + Butanoic Acid called?
Condensation reaction

(condensation between a hydroxyl, OH and a hydrogen, H)
Saponification of esters in the presence of NaOH and heat produces what two general products?
Soap and alcohol
Hydrolysis of an ester produces what two molecules?
Carboxylic acid + alcohol
Can ether functional groups hydrogen-bond amongst themselves?
No. (Hydrogen bonding requires a hydrogen bonded to a highly electronegative atom like N, O, or F)
Compare the boiling point between an ether and an alkane with an equivalent molecular weight.
The boiling point of the alkane is lower than the ether because the polar C-O bonds in the ether cause greater intermolecular forces and higher boiling points in ethers.
Ethers can be formed in the presence of concentrated sulfuric acid (H2SO4) and two molecules of what?
Alcohol.

This is a condensation reaction between a hydroxyl, OH group from one alcohol and a hydrogen, H from another alcohol
Is this amine 1˚, 2˚, or 3˚?

What type of amine cannot form hydrogen bonds with itself?
3˚ amines

(Both 1˚ and 2˚ amines can form hydrogen bonds)
Which has the highest boiling point, an amine or alcohol (of similar molecular weight)?
The alcohol has the higher boiling point because the OH hydrogen bonding in alcohols is stronger than the NH hydrogen bonding in amines.
Treating an alkyl halide with ammonia in the presence of NaOH produces what type of molecule?
Amine
Can amides form hydrogen bonds with other amides?
Yes.

(The N-H can hydrogen bond)
What is the name of reaction between an amide and carboxylic acid?
Condensation reaction
Combining what two functional groups can synthesize amides?
Combining (secondary) amines and carboxylic acids.
Hydrolysis of an amide yields what functional group products?
Carboxylic acid + amine
Reduction of an amide (with LAH) will yield what functional group?
Amine
Reacting an ester and ammonia will yield what two functional groups as products?
Alcohol + Amide
What is an aromatic molecule?
An unsaturated ring structure with alternating double bonds.
Does an aromatic ring have to contain 6 carbon atoms?
No, the ring could contain 10 carbons, or any combination of (4n + 2 carbons, or pi electrons)
What does a molecule of phenol look like?
Are the following compounds all aromatic?

Aniline, Toluene, Phenol.
Yes, monosubstituted benzene rings are still aromatic.
Does a benzene ring have the same structure as a phenyl group?
No, when a benzene ring is a substituent it is called a phenyl group. The phenyl group has one less hydrogen atom than benzene because it must bond to the main molecule at this position.
Are all carbohydrates polymers?
No. While most carbohydrates are polymers of several monosaccharides, technically glucose (a monosaccharide) is a carbohydrate.
Carbohydrates are polymers of monosaccharides, called polysaccharides. What is the polymer of protein called? What are the subunits of protein?
The polymer of protein is the polypeptide. The subunits are amino acids.
What type of reaction joins two glucose monosaccharides?
Condensation

(between adjacent hydroxide groups)
What type of reaction joins two amino acid monosaccharides?
Condensation

(between adjacent amine and carboxylic acid groups)
What type of bond joins two amino acid monosaccharides?
Peptide bond
Can amino acids be acidic or alkaline?
Yes
Can amino acids be hydrophilic or hydrophobic?
Yes
What causes the primary structure of polypeptides to form secondary structures?
Hydrogen bond interactions between the amino acids in the polypeptide

Structure and Properties of Matter

Atomic Structure

The region around an atom where an electron is most likely to be found is called an energy level. Solution
The energy levels are discrete energetic regions where electrons are located, with a high probability.

The Aufbau Principle

Electrons fill orbitals in the following order: 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f ... Solution
Aufbau Principle:
Electrons are placed in the lowest energy subshell available. Orbitals hold up to two electrons. Electrons must occupy each orbital of a subshell before being paired up.

Electrons fill in the following order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d ...

The highest energy sublevel in a Titanium, Ti atom is: Solution
Electrons fill in the following order of sublevels from low to high energy: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d ...

Aufbau principle - fills lower energy sublevels first. Notice the 3d sublevel has higher energy than the 4s because it is filled after 4s, despite being a lower energy level, n.

Electron Configurations

The shorthand, ground state electron configuration for Silicon is [Ne] 3s24p2 Solution
The shorthand, ground state electron configuration for Silicon is [Ne] 3s23p2

Electron Configurations: Half-filled d Orbital

The ground-state electron configuration 1s2 2s2 2p 6 3s2 3p 6 4s1 3d5 is for the element... Solution
Chromium (Cr) takes this configuration because there is extra stability from the half-filled d orbital.
This occurs with the other elements in the same group: Molybdenum (Mo) and Tungsten (W).

(The 6 elements with unexpected configurations are Cu, Ag, Au, and Cr, Mo, W).

Electron Configurations: s Vs. d Orbital

The ground state electron configuration for Copper is Solution
This same thing occurs for the other elements in the same group as Copper (Cu): Silver (Ag) and Gold (Au).

The expected configuration: 4s2 3d9
The actual, more stable configuration: 4s1 3d10

The valence electrons are more stable when the s sublevel is half full and the d sublevel is full.

Electron Configurations: Transition Metal Ions

The Iron atom Fe3+ is formed by when iron loses Solution Video
Iron is multivalent, most common is Fe3+. Ground state iron has 6 electrons in the 3d shell, and 2 electrons in the 4s.

The higher energy 3d loses 1 electron, to become half full. The lower energy 4s loses both electrons to become empty.
1s22s22p63s23p64s23d6 ... 1s22s22p63s23p64s03d5 = 1s22s22p63s23p63d5 Writing 4s2 before 3d6 follows the Aufbau principle order, however some other sources show the other way with 3d before 4s.

Sublevels and Orbitals

The p sublevel contains how many orbitals? Solution
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There are 3 orbitals in the 'p' sublevel. (1 orbital in the 's' sublevel, and 5 orbitals in the 'd' sublevel).

Orbital

One orbital can not have which of the following? Solution
One orbital can hold up to 2 electrons with opposite spins. They can be empty, with zero electrons. Note that orbitals should not be confused with 'octet'. '

Electron Configuration: Orbitals

The number of orbitals in the 3rd energy level is Solution
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Number of orbitals = (n energy level)2 = (3)2 = 9

Rutherford's Gold Foil Experiment

Ernest Rutherford's observations of alpha particle deflection from gold foil allowed him to conclude that the nucleus was a large proportion of the atom. Solution
The reflection of any alpha particles at all was surprising proof that the atom did contain something inside it.

However, only a small number of alpha particles were deflected, so the atom was mostly empty space with a very small nucleus. The large majority of an atom is the electron cloud. Rutherford coins the term 'proton' in 1914.

Geiger–Marsden (Rutherford's) Gold Foil Experiment

If Thomsons's atomic model (1897) was correct, Rutherford would have observed which of the following during the gold foil experiment? Solution
Thompson's model spaced the negatively charged particles evenly throughout a positively charged substance in the atom, like a "plum pudding", or chocolate chips in a cookie. The alpha particles need a mass like a nucleus to reflect, and would not be reflected from these tiny, lone subatomic particles in Thomson's model.

The Photoelectric Effect

The photoelectric effect is one of the experiments that demonstrates light behaves not just as waves, but as particles too. Solution
Light clearly behaves as electromagnetic waves, and the photoelectric effect shows that light behaves is discreet quanta of energy as photons or particles. The experiment involved shining light at a certain frequency on a metal to cause electrons to be released. Although Hertz did this experiment in 1887, it was Einstein who used it in 1905 to explain the quantum (packet) energy of light depends on its frequency. Einstein later won the Nobel Prize for this explanation in 1921.

Isotopes and Mass Spectrometer

A mass spectrometer measures the Solution
A mass spectrometer accelerates the particles (charges) through a uniform magnetic field, and the amount of deflection or curvature indicates the mass.

Different masses of ions were explained by different numbers of neutrons: isotopes!

Isotopes and Mass Spectrometer

Heavier isotopes are deflected more than lighter isotopes in a mass spectrometer. Solution
A mass spectrometer accelerates the particles (charges) through a uniform magnetic field, and the amount of deflection or curvature indicates the mass.

Heavier isotopes are deflected less in a mass spectrometer. Their radius of curvature is larger.

Bohr Theory

Bohr's theory of atomic structure was based on the idea that electrons orbit the nucleus on energy levels and when discreet quanta of energy is absorbed, electrons can transition or jump to higher energy levels. Conversely when electrons return or fall back down to lower energy levels, discreet quanta of energy, called photons are released. Solution
When discreet quanta of energy is absorbed, electrons can transition or jump to higher energy levels.

When electrons return or fall back down to lower energy levels, discreet quanta of energy, called photons are released.

The discrete quanta is based on the distance between energy levels and partly shows the existence of energy levels in atoms.

Quantum Numbers

What does the secondary quantum number represent? Solution
Principal Quantum NumbernEnergy Level, or Shell, n = 1, 2, 3, 4...
Secondary, Azimuthal Quantum NumberlSublevel/Subshell, (0)s, (1)p, (2)d, (3)f
Third, Magnetic Quantum NumbermlOrientation, _, _ _ _, _ _ _ _ _, _ _ _ _ _ _ _.
Fourth, Spin Quantum NumbermsElectron Spin, +½, -½
Get the range of l... ±l = n-1 The second, azimuthal quantum number allows the third quantum number to be determined. For example, for
n = 1 →→ l = 0 →→ 0 →→ s sublevel
n = 2 →→ l = 0, 1 →→ -1, 0, +1 →→ p sublevel
n = 3 →→ l = 0, 1, 2 →→ -2, -1, 0, +1, +2 →→ d sublevel

S (shart), P (principal), D (diffuse), F (fundamental)... these sublevels or subshells have different shapes.

Quantum Numbers

For the principle quantum number of n = 3, which of the following are the values of secondary azimuthal, l and magnetic, ml quantum numbers, respectively? Solution
  1. 1 only
  2. 2 only
  3. 3 only
  4. 0, or 1
  5. 0, or 1, or 2
  6. 1, or 2
  7. 1, or 2, or 3
  8. -1, 0, 1
  9. -2, -1, 0, 1, 2
  10. -3, -2, -1, 0, 1, 2, 3
Secondary quantum number, l = (n-1)
l = 3 - 1
l = 2 (l can be a maximum of 2: 0, or 1, or 2)
for the highest l = 2, then ml is from -2 --> +2

Magnetic quantum number is from -l to +l. The secondary quantum number indicates the shape of the electron orbit on subshells from the number of values for l. The magnetic quantum number is the number of orientations of orbitals that can exist. E.g.) A secondary quantum number = (1)p would have the following number of orbitals (_ _ _) according to (-1, 0, 1).

Quantum Numbers

An atom with the quantum numbers, n = 2 and l = 2, has 8 electrons in the shell. Solution
The following combination of quantum numbers is not possible: n = 2 and l = 2.

The secondary, azimuthal quantum number (l) is (n-1) = 1. So n = 2 and l = 1.

(It is true that there are 8 electron in the 2s, 2p shell).

The quantum number responsible for explaining the interaction of atoms with magnetic fields is called the magnetic quantum number, ml. Solution
This is misleading. The magnetic quantum number actually describes the electron's orientation/location in space, with one, three, or five possible orientations according to the following positions:

ml = 0
ml = -1, 0, or 1.
ml = -2, -1, 0, 1, or 2.

It is actually the different spin of electrons (+½, -½) from the spin quantum number, m2 that explains if the atom will be attracted or repelled by a magnetic field. Paired electrons are diamagnetic and are not attracted to magnetic fields, rather slightly repelled. Unpaired electrons are paramagnetic and are attracted to magnetic fields.

Which of the following symbols corresponds to the quantum numbers: n = 2, l = 1? Solution
The principal quantum number (n)
The second, azimuthal quantum number (l)
The third, magnetic quantum number (ml)
The fourth, spin quantum number (ms).
n = 2 → this tells us it's in the 2nd energy level.
l = 1 → this tells us the number of orbitals in the sublevel from -l to +l, which would be -1, 0, +1 → which is 3 orbitals → the p sublevel has 3 orbitals.

State the maximum number of electrons in an atom that can have the following quantum numbers in total in all principle quantum rows (n) and any sublevel: n = 2, ml = 0. Solution
Using the first quantum number (n = 2), there are 2 azimuthal values (l) from 0 to (n-1): 0, 1

The two azimuthal values are written from -l to +l, giving us the number of orbitals in a sublevel:
0 = 1 orbital in s
-1, 0, +1 = 3 orbitals in s.

2s has 2e- with Ml = 0
2p has 2e- with Ml = 0.

2e- + 2e- = 4e-

Think of this like a notation for each orbital containing electrons:
  1. n = 2, l = 0, ml = 0
  2. n = 2, l = 1, ml = -1
  3. n = 2, l = 1, ml = 0
  4. n = 2, l = 1, ml = +1
See that there are 4 possible combinations, with 2 ml values.

(Note that we don't count the n=1 sublevel 1s, which has a ml=0

Quantum Numbers: f-block

The f sublevel has 7 orbitals and the d sublevel can hold 10 electrons. Solution
True, the f sublevel has 7 orbitals and the d sublevel can hold 10 electrons.

What energy levels are the f-blocks in? [2] Solution
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4-f & 5-f

(Not 6 & 7 as many people think)

Pauli Exclusion Principle

Two electrons in the same orbital have the same spin directions. Solution
Wolfgang Pauli, Austrian physicist (1900-1958). The Pauli exclusion principle states that no two electrons in an atom have the same four quantum numbers: principle n, secondary l, magnetic ml, and spin ms.

Hund's Rule

The 2p subshell in an oxygen atom contains the following electron configuration Solution
Each of the three orbitals must fill with at least one electron before the electrons begin to pair up.

An orbital can hold up to 8 electrons Solution
An orbital can only hold up to 2 electrons. Orbitals are not to be confused with subshells, which contain orbitals, and have the same values of n and l, e.g. 2s, 3p...

Heisenberg's uncertainty principle

"The more precisely the position [of a subatomic particle] is determined, the less precisely the ____________ is known in this instant, and vice versa." Solution
Hint Clear Info
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Hint Unavailable
"The more precisely the position [of a subatomic particle] is determined, the less precisely the momentum is known in this instant, and vice versa." -Heisenberg

Max Planck's Explanation of Blackbody Radiation

Max Planck's experiments with blackbodies (perfectly black objects that emit, rather than reflect light) showed that energy of atoms in solids are not quantized, rather the energy is continuous. Solution
The experiment(s) showed that energy of atoms in solids are quantized, and not continuous.

The spectrum curves appear continuous when presented on a simple line graph, but this line actually misrepresents the very small differences in discreet, quantized energies. These 'quanta' of light energy are photon particles.

Electronegativity

Which of the following covalent bonds has the highest polarity? Solution
Oxygen has the highest electronegativity of all the elements included here. Therefore the electronegativity difference with hydrogen will be highest, giving the O-H bond the highest polarity.

Hydrogen Bonding

Hydrogen bonding is possible whenever a molecule contains hydrogen bonds Solution
Hydrogen bonding is possible whenever the molecule contains hydrogen atoms bonded to N, O, and F atoms

Central Atoms

In addition to carbon, sulfur and phosphorus can act as central atoms in a compound. Solution
And they can form more than an octet on the central atom: SF6 and PCl5

Bonding and Electron Configurations

Determine the compound that will form by combining an element that has the electron configuration [Ne]3s2, plus Oxygen. Solution
[Ne]3s2 is Magnesium, Mg and forms a Mg2+ cation because it is in group two and can easily donate the two electrons to become isoelectronic with the noble gas Neon.
Oxygen forms an O2- anion because it is in group 6A (16) and can easily gain two more electrons to get a full octet.

The net charges are balanced in the electron transfer: Mg2+O2-

Since the charges are balanced, the compound takes one of each cation and anion: MgO.

Lewis Diagram

The Lewis structure of an atom with the electron configuration 1s22s22p63s23p4 would have Solution
One pair in the 3s sublevel, one pair and two unpaired in the 3p sublevel.

Lewis Diagram

The lewis structure of a molecule of carbon dioxide, CO2 would display how many total electrons? Solution
Hint Clear Info
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CO2 has 4 valence electrons in carbon, and 6 valence electrons in each oxygen.

4 + 6 + 6 = 16.

Lewis Diagram for Ions

A lewis structure for the Scandium ion, Sc3+ would contain how many electrons? Solution
The scandium has given away three electrons to become the Sc3+ ion, leaving the valence shell with zero electrons remaining.

Lewis Diagrams for Ionic Compounds

Draw lewis diagrams for the following molecules

NaCl Solution

MgBr2 Solution

Li2S Solution

CaO Solution

Lewis Diagrams for Covalent Compounds with Single Bonds

Draw lewis diagrams for the following molecules using the rules below:

StepWhat to Do
1Arrange the atoms with the element that forms most bonds in the central position.
2Add the total number of valence electrons.
3Start by placing one bonding pair of electrons between each atom.
4Put remaining electrons as lone pairs on all atoms except central atom, to a maximum octet of 8 electrons per atom.
5If octet on central atom is incomplete, move peripheral lone pairs into bonding electrons that are shared with the central atom.
6Make sure central and peripheral atoms have complete octets. Now if there are extra electrons, place these as lone pairs on the central atom (*exception to octet rule).

NF3 Solution
Trigonal pyramidal (a.k.a. Pyramidal)

H2S Solution Video
Bent (this is not linear because the two lone pairs will bend the molecule in 3D space due to the high repulsion).

CH3Cl Solution
Tetrahedral

C2H6 Solution

PCl3 Solution
Trigonal pyramidal (a.k.a. Pyramidal)

Lewis Diagrams for Charged Compounds

Draw lewis diagrams for the following molecules

H3O+ Solution
Trigonal pyramidal.

NH4+ Solution
Tetrahedral

NO3- Solution
Trigonal planar

CO32- Solution
Trigonal planar

SO42- Solution
Tetrahedral (many dative bonds)

HCO3- Solution
Trigonal planar

Lewis Diagrams for Covalent Compounds with Double or Triple Bonds

Draw lewis diagrams for the following molecules

O2 Solution
Linear

P2H2 Solution

C3H6 Solution

C2F2 Solution
Linear

SO2 Solution
V-shaped

HCN Solution
Linear

N2O Solution
Linear

Lewis Diagrams for Covalent Compounds with Exceptions to the Octet Rule

Draw lewis diagrams for the following molecules

BF3 Solution
Trigonal planar (like BI3, BCl3, BBr3, BH3...)

SO3 Solution
Trigonal Planar

XeF4 Solution
Square Planar

H2SO4 Solution
Tetrahedral

PI5 Solution
Trigonal Bipyramidal

SF6 Solution
Octahedral

Using Orbitals to Explain Bonding Exceptions

Explain how SF6 can have 12 electrons around the central Sulfur. Use orbitals in your explanation, and determine all the different bond angles. [3] Solution
Hint Clear Info
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Hint Unavailable
This hybridizes to sp3d2, or one in 's' three in 'p' and 2 in 'd'.

This creates space for 6 bonds with each of the unpaired electrons.

The different bond angles are: 90˚, 120˚, and 180˚.

VSEPR Shapes

The molecular geometry of the NH3 molecule is predicted by VSEPR to be... Solution
See the 3D shape is Trigonal Pyramidal... A pyramid with a three-sided base It doesn't matter if it's drawn 2-dimensionally... (Note that the 'electron group geometry' is tetrahedral).

NF3 is trigonal pyramidal, while BF3 is trigonal planar. Use your understanding of Lewis diagrams and VSEPR theory to briefly explain. [2] Solution
Hint Clear Info
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Think about what causes the differences in molecular geometries
Nitrogen has 5 valence electrons, and forms 3 covalent bond plus one lone pair. The lone pair of electrons in NF3 repels the three fluorine atoms downwards, to create the trigonal pyramidal molecule geometry with ~107˚ bond angles.

Boron has 3 valence electrons, and forms 3 covalent bonds, with no lone pair. The three identical fluorine atoms arrange themselves furthest apart in space, forming 120˚ bond angles.

VSEPR Theory

The VSEPR shape of a molecule with 2 lone pairs and 2 bonding pairs is called, Linear. Solution
This molecule is V-shaped.

VSEPR Theory

Predict the molecular geometry (not electron pair arrangement) and state the polarity for the following compounds. Make a sketch in your own notes, if it helps.

BH3 Solution
Hint Clear Info
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Hint Unavailable
Trigonal Planar, Non-polar

PCl3 Solution
Hint Clear Info
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Hint Unavailable
Trigonal Pyramidal, Polar

H2O Solution
Hint Clear Info
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Hint Unavailable
Bent (V-shaped), Polar

CO2 Solution
Hint Clear Info
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Hint Unavailable
Linear, Non-polar

SiH4 Solution
Hint Clear Info
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Hint Unavailable
Tetrahedral, Non-polar

PF5 (Extended) Solution
Hint Clear Info
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Hint Unavailable
Trigonal Bipyramidal, Non-polar

Valence Bond Theory

Fill in the blank: Two _________ orbitals overlap to form a bonding orbital, that contains a maximum of two electrons.

Hybridization

Show with a series of sketches, how the orbitals in the s and p subshells combine to form hybridized bonding orbitals between one carbon atom and four hydrogen atoms.

Hybridization

How many pi bonds are found at the central carbon atom in carbon dioxide, CO2? Solution
Hint Clear Info
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Hint Unavailable
The central carbon has 2 sigma bonds, and 2 pi bonds, with a total of 4 bonding-pairs of electrons.

One s orbital and two pairs of p orbitals overlapping creates a triple bond. Solution
Ethyne is an example where this occurs in the C-C bond.

Dipole Polarity of Molecules

Determine the polarity (polar or non-polar) of the following molecules.

HCl Solution
Hint Clear Info
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Hint Unavailable
polar

BH3 Solution
Hint Clear Info
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Hint Unavailable
non-polar

NH3 Solution
Hint Clear Info
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Hint Unavailable
polar

O2 Solution
Hint Clear Info
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Hint Unavailable
non-polar

CH4 Solution
Hint Clear Info
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Hint Unavailable
non-polar

CH3Cl Solution
Hint Clear Info
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Hint Unavailable
polar

HO Solution
Hint Clear Info
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Hint Unavailable
polar

Molecular Forces

Which of the following is the strongest intermolecular force? Solution
Hydrogen Bonding is the strongest

The van der Waals intermolecular force is composed of two forces: dipole-dipole and London. Solution
True

Increasing the number of electrons would increase the London force Solution
London forces are caused by the attraction of the electrons from one molecule to the positive centre in an adjacent molecule. So, the strength of the London force is directly proportional to the number of electrons (and/or protons) in the molecule(s).

Molecular Forces

Describe the following types of intermolecular forces.

London Dispersion. [2] Solution
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London Dispersion is the weakest intermolecular force, which is temporary and induced by dipole moments. These forces exist in both polar and non-polar molecules. While polar molecules have many different types of forces, non-polar molecules only have London dispersion forces.

Hydrogen Bonding. [2] Solution
Hint Clear Info
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Hint Unavailable
Hydrogen Bonding is the strongest intermolecular force. These forces exist mostly in polar molecules (but there are exceptions). The force itself is polar. Only hydrogens bonded to Nitrogen, Oxygen, or Fluorine can form hydrogen bonds with other electronegative atoms. Hydrogen bonds are not actually bonds, rather they are more of an attraction.

Molecular Forces: Physical Properties

Order the following compounds from high to low boiling point. Solution
C5H8
C4H10
C2H6
C3H4
C5H12
Melting and boiling point is proportional to the molecular weight (g/mol) of the molecule if all functional groups are the same. Each of the given compounds are just simple hydrocarbons with the same intermolecular forces, so only the molecular weight is compared. The London dispersion intermolecular force is too weak to cause any significant increase in boiling point.

Use your understanding of polarity, molecular forces, and molecular mass to determine which compound will have the lowest melting point. Solution
The weakest force is non-polar London forces. This is in the non-polar CO2 and CH4 molecules. Between these two CH4 has the lower melting point because it is lighter (lower molecular mass, g/mol): 16.04g/mol compared to 44.01g/mol for the CO2.

Explain the types of intermolecular forces in the following molecule, and why there is a difference in the boiling points. Solution
MoleculeBoiling Point (˚C)
Nitrogen, N2-195.8 ˚C
Carbon Monoxide, CO-191.5 ˚C
Iso-electronic species, meaning same number of electrons. Comparing the intermolecular forces, non-polar nitrogen has London, and polar carbon monoxide has van der Waals (London + Dipole). The stronger van der Waals forces causes the molecules to be more attracted to one another and it is harder for the molecules to split apart as the phase changes from liquid to a gas - hence the higher boiling point for carbon monoxide.

Explain how water travels up thin glass tubes (capillary action) using the terms cohesion and adhesion. Solution
  • Molecules stick to themselves in cohesion
  • Molecules stick to something else in adhesion
  • For thin tubes with low surface area, the adhesion is greater than the cohesion in water. The intermolecular force between the water and glass pulls the water up the glass by capillary action
  • It is necessary to have strong intermolecular forces in the cohesion to pull the molecules upward. For example, liquid mercury metal does not undergo capillary action.

Explain how a safety pin floats on the surface of water when placed horizontally, but sinks when placed vertically, using the terms cohesion and adhesion. Solution
  • The surface tension of the water is due to cohesion (sticking of the water molecules amongst themselves)
  • If the mass of the safety pin is low and the surface area in contact with the water molecules is high, then the pin will be supported by the strong cohesion of the water molecules underneath
  • When the pressure of the pin is increased by placing it vertically, the weight is great enough to separate the cohesion intermolecular force between the water molecules and the pin pulls apart the water molecules to fall and sink

Electrolytes

Which of the following can conduct electricity in either a solid, liquid, gaseous, or aqueous state? (More than one answer: check all that apply) Solution
Metallic elements can conduct in the solid and liquid phase (like copper wire, or molten gold), while ionic can conduct only when in the aqueous state (like electrolytes, e.g. saltwater).

Crystal Structure

Describe the relation between the lattice and the unit cell. [2] Solution
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
  • There are many different types of unit cells (over 14), that are the smallest repeating unit, which combine to form the organized lattice grid structure.
  • The atoms are arranged on the lattice points, in various configurations, forming various crystal structures.
  • Pure crystals are made of these lattice arrangements.

Classify the type of unit cell below. Solution
This is a face-centered cubic.

Classify the type of unit cell below. Solution
This is a body-centered cubic.

Physical Properties of Ionic Crystals

State at least one physical property of ionic crystals. [1] Solution
Creative Commons Credit: Michel32nl, nl.wikipedia, 2004
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
Some physical properties
  • High melting and boiling point because of the ionic bonds
  • Crystals are brittle and hard
  • The solid crystals do not conduct electricity (unless molten liquid, or dissolved as aqueous)

Metallic Crystals

What property of metallic crystals forms the bond and also allows these crystals to conduct electricity? Solution
Hint Clear Info
Incorrect Attempts:
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Hint Unavailable
The answer is looking for:
  • The "sea of electrons" or "delocalized electrons"
These negatively charged electrons form the bond between the nuclei and also propagate any current through the material.

Metal Crystals

All natural and processed metals exist in a single crystal form. Solution
False. You might think this because of the densely packed atomic structure of metals, but the malleability of metals allows the metal to be compact, without being a single crystal.

You can make metal crystals though the process of repeatedly heating and cooling... Crystals are typically stronger structures. In nature, crystals are occasionally formed, but more slowly over hundreds or millions of years.

Strength of Metal Crystals

Determine the most significant factor contributing to the strength of pure, elemental metallic crystals. Solution
The positively charged nucleus and the negatively charged sea of electrons is the basis for the strength of atomic bonding. Elements with a greater nuclear charge and number of valence electrons will be stronger and have higher boiling/melting points.

Note that the metal with the greatest atomic mass doesn't necessarily have the strongest bonds because you have to take into account the atomic radius; greater distances reduce the net force due to inner electrons shielding the outer...

Types of Crystals

Classify the type of crystal with the following properties... Solution Doesn't conduct electricity, low melting point, soft.
Molecular (covalent) compounds do not conduct electricity because there are no free electrons or charged particles. They have a relatively low melting point, and are relatively soft crystalline solids because of the weak intermolecular forces in the crystal.

There is a wide range of molecular crystal strengths from strong quartz (SiO2) to weaker sucrose sugar (C12H22O11).

Sucrose sugar crystals are what type of crystal? Solution
Sucrose sugar is polar molecules that form molecular crystals.

Which of the following is the strongest type of crystal? Solution
Covalent network (macromolecular - molecules with very large numbers of atoms) are the strongest because they are truly one molecule connected by covalent bonds.

Molecular Crystals

What are the possible forces within molecular crystals? Solution
Van der Waals forces are made of induced London dispersion force and/or permanent dipole-dipole force. Basically Van der Waals is any force except for covalent and ionic. This is the most accurate

Covalent Network Solids

Covalent network crystals are ____________ electrical conductors and are ____________ in most solvents. Solution
Covalent network crystals are poor electrical conductors and are insoluble in most solvents.

Carbon Crystals

C60 Fullerines are crystals. Solution
Yes they are considered crystals. They are covalently bonded macromolecules that have a high boiling/melting point

Which of the following carbon-containing solid can conduct electricity? Solution
Actually, graphite can conduct electricity due to its special form. The sp2 hybridized carbons have π bonds above and below the plane of the sheets. These π bonds overlap and form an extensive bonding network. The delocalized π electrons move freely around the sheet... conducting electricity.

Flashcards: Structure and Properties

Who developed the most generally accepted model of the atom?
Niels Bohr
What causes emission and absorption?
Electrons orbit the nucleus on energy levels and when discreet quanta of energy is absorbed, electrons can transition or jump to higher energy levels. Conversely when electrons return or fall back down to lower energy levels, discreet quanta of energy is released as emission.
Which transition has a greater change in energy?
2 → 1 or 4 → 3
2 → 1
How many energy levels are in the 24Mg atom?
3
Does O2- and F1- have the same number of protons?
No, the number of protons are always different for different elements. O2- and F1- have the same number of electrons.
What is the principle quantum number (n) ?
The energy level (shell) number
What is the second, azimuthal quantum number (l) ?
The subshell: s, p, d, or f
What is the third, magnetic quantum number (ml) ?
The specific orbital within a subshell
What is the fourth quantum number (ms) ?
The electron spin, +½ or -½
What is the Pauli exclusion principle?
Two electrons in the same atom can never have the same 4 quantum numbers
What is the maximum number of electron in the first, second, and third energy levels?
= 2n2

= 2, 8, 18
What are the possible orbitals within the p subshell?
p = -1 → +1

= -1, 0, +1

= 3 orbitals
How many valence electrons are in the atom?
[Ne] 3s24p2
4

(2 in the s and 2 in the p)
What is Hund's rule?
Electrons will fill the subshell with single electrons in each orbit before forming pairs in an orbit because half-filled orbitals are stable.
What is Heisenberg's uncertainty principle?
"The more precisely the position [of a subatomic particle] is determined, the less precisely the momentum is known in this instant, and vice versa." -Heisenberg
What is paramagnetic and diamagnetic?
Paramagnetic materials have unpaired electrons in orbitals and are attracted to magnets.

Diamagnetic materials have all paired electrons in orbitals and are repelled by magnets.
The Ca2+ cation loses electrons from what subshell/sublevel?
s
How many electrons can fit in one d sublevel?
10
What fills first, 4s or 3d?
4s
What fills first, 3d or 3p?
3p
What has a higher energy, 4s or 3d?
3d

(the lower energy sublevel, 4s fills first)
Evidence from what apparatus indicated the existence of isotopes of elements?
Mass spectrometer
Would this be paramagnetic or diamagnetic?
Paramagnetic
Determine the valence electron configuration of carbon, which has 4 valence electrons
2s22p2
What is a sigma (σ) and a pi (π) bond?
A sigma bond is a single bond, a pi bond is a double bond that can only occur with the presence of a sigma bond.
What are the components of a triple bond?
1 sigma and 2 pi bonds
Can some electrons have a full valence without 8 electrons?
Yes, hydrogen and helium have a full valence with 2 electrons
How does bond length compare to bond strength?
Shorter bonds are stronger.
How does bond length compare to the number of bonds?
More bonds are shorter in length, for example triple bonds are shorter than single bonds.
What type of bond would form with the following electronegativity ranges?
0 - 0.5
0.5 - 1.7
1.7 +
Non-polar covalent
Polar covalent
Ionic
How many total electrons are distributed in a lewis structure of NH3?
8
What are resonance structures?
Structures that differ in lone pair arrangement and bonding, but with the same relative positioning of the atoms
What is the bond angle in a tetrahedral arrangement?
109.5˚
What is the electron arrangement of a carbon dioxide molecule?
linear
What is the electron arrangement of a water molecule?
tetrahedral
What is the electron arrangement of a molecule with two single bonds, and one lone pair?
trigonal planar
What is the electron arrangement of an ammonia (NH3) molecule?
tetrahedral

(don't forget about the lone pair)
What is the strongest intermolecular force?
Hydrogen bonding
How does intermolecular force affect melting and boiling point?
Stronger intermolecular forces have higher melting and boiling points

Thermochemistry - Energy Changes

Specific Topic General Topic School Date
Enthalpy of Reaction ∆Hrxn Equation North Toronto Nov 2013
Enthalpy of Reaction ∆Hrxn Hess's Law North Toronto Nov 2013
Pathways of Simple Chemical Reactions

Given a graph of the energy during a reaction pathway.

Which of the following represents the activation energy, Ea? Solution
Activation energy (Ea) is the energy required for the reaction to progress from the reactants to reach the temporary intermediate state at which the molecules in rearranged and bonds are broken and new bonds start to form. = 'A' This energy 'hump' represents a threshold or barrier for the reaction to overcome for the reaction to proceed. Catalysts (like enzymes or certain metals) lower the activation energy and increase the rate of reaction.

Which of the following represents change in enthalpy, ∆H? Solution
Enthalpy (∆H) is the difference in energy between the reactants and products. When products have less energy, -∆H is exothermic. When products have more energy, +∆H is endothermic. The difference between products and reactants 'C' is the enthalpy, ∆H. (Also could be A - B) In this graph it is endothermic, +∆H.

Heat Exchange

An increase in heat in a system is indicated as: Solution
For heat in a system:
+ q is an increase,
- q is a decrease.

Thermochemistry: Exothermic and Endothermic

Endothermic reactions have heat on the right side of the equation Solution
Endothermic reactions absorb heat, therefore heat is on the same side as the reactants.

In endothermic reactions Solution
Because energy is absorbed giving the products more potential energy than the reactants.

Thermochemistry: Exothermic and Endothermic

The following reaction is exothermic. Solution
Heat is released when the water condenses from higher energy gas to a lower energy liquid. This heat must go somewhere into the surroundings, which makes this condensation reaction exothermic.

Cold packs feel cold because they absorb heat from the surroundings and are exothermic. Solution
Cold packs feel cold because they absorb heat from the surroundings and are endothermic.

Determine which of the following is an endothermic process. Solution
Photosynthesis is endothermic because the plant cells gain (light) energy from the Sun.

Thermochemistry: Exothermic and Endothermic

On a potential energy diagram, the enthalpy change, ∆H is assumed to be the amount of heat released or absorbed during the reaction progress. Solution
This is true for adiabatic reactions (constant pressure, pressure is unconstrained). Enthalpy is based on the change (∆) in heat because enthalpy cannot be measured directly, without a change.

Systems

A closed system can Solution
It is closed to the exchange of matter only, not heat. For example, hot and cold packs can exchange heat, but not matter.

In isolated system cannot exchange matter nor energy with the surroundings. Solution
Think of an isolate system like a closed system that has perfect insulation, and therefore does not exchange heat.

(Contrast that with an open system, which allows the transfer of both matter and energy with the surroundings).

Which of the following is an example of an isolated system? Solution
Isolated systems have no change of mass or heat. Only the vacuum chamber has absolutely no change in either.

Definition of Specific Heat

Specific heat is defined as Solution
The energy required to raise the temperature of one gram by 1˚C

(Note that this is the same as raising the temperature of one gram by 1 Kelvin since ∆˚C = ∆K)

Specific Heat Capacity Theory

The international standard units of specific heat capacity are: Solution
J/(g·˚C)

(and sometimes stated as J/kg·˚C).

Specific Heat Theory

What unit of temperature is used for the change in temperature in the equation q = m c ∆T? Solution
  1. Kelvin
  2. Celsius
  3. Joules
  4. Calories
The magnitude of the change (∆) in temperature (∆T) would be the same for a change in Kelvin or degrees Celsius. For example +100K = +100˚C

What unit of energy is used for heat in the equation q = m c ∆T. Solution
  1. Kelvin
  2. Celsius
  3. Joules
  4. Calories
The Joule is a unit of heat, and energy.

Calorimetry

A calorimeter measures Solution
A calorimeter is a device used to measure changes in heat in chemical and physical reactions.

Processes

Isobaric means constant pressure, and adiabatic means no heat exchange. Solution
'Iso' means equal and bar is a unit of pressure, so iso-baric means equal pressure.

Adiabatic systems do not exchange heat.

Specific Heat

If the specific heat of aluminum is 2.01 J/(g·˚C), how much heat is required to raise the temperature of 2 g by 1˚C? Solution
Hint Clear Info
Incorrect Attempts:
CHECK
J
Hint Unavailable

Specific Heat: q = m c ∆T

100 J of heat is added to a 25 g unknown block at 5.45˚C causing the block to heat to 10.00˚C. Determine the identity of the unknown sample. Solution

Specific Heat: q = nH

Calculate the heat required to vaporize 100 g of nitrogen gas at -196˚C if the enthalpy of vaporization of nitrogen is 5.56 kJ/mol Solution
q
Hint Clear Info
Incorrect Attempts:
CHECK
kJ
Hint Unavailable
Molar enthalpy is given here, in kJ/mol...

Specific Heat, 2 Samples, Find mass: q = m c ∆T

The laboratory scale is broken and a chemist needs to figure out the mass of a known sample of pure silver. The chemist has a heat source, calorimeter, and thermometer to use so they decide to find the mass using calorimetry. Starting at room temperature, 25˚C, the sample is placed in the calorimeter and immersed in 0.45kg of water (4.18 J·g-1·˚C-1). It takes 142,875 J of heat to bring the sample to a boil at 100˚C. Given the specific heat capacity of silver is 0.240 J·g-1·˚C-1, determine the mass of the silver. Solution
Hint Clear Info
Incorrect Attempts:
CHECK
g
Hint Unavailable
Make sure to plug in 450g for water, and not 0.45kg

Specific Heat, 2 Samples, Find Tf: q = m c ∆T

Equal masses of ethanol (2.46 J·g-1·˚C-1) and water (4.18 J·g-1·˚C-1) are mixed to form a 700g solution at room temperature, 298K. The solution is heated with 124,031.88 J of energy.

Total Heat Added = Heat gain in Ethanol + Heat gain in Water

Determine the final temperature of the mixture. Solution
Tf =
Hint Clear Info
Incorrect Attempts:
CHECK
K
Hint Unavailable

Specific Heat, 2 Samples, Find Tf Mass Ratio: q = m c ∆T

A 1,050 ˚C glowing-hot block of gold (0.129 J·g-1·˚C-1) is placed in a calorimeter filled with nothing but air (1.02 J·g-1·˚C-1) at room temperature, 298K. If the mass of gold is 5 times the mass of air, calculate the final temperature in the calorimeter assuming no heat loss. Solution Video
Tf =
Hint Clear Info
Incorrect Attempts:
CHECK
˚C
You don't need mass. Mass cancels when you set the heat of gold equal to the heat of air.
Let the mass of the air be m, and the mass of the gold be 5m.
IMPORTANT: gain in heat = +q, loss of heat = -q

Specific Heat With Phase Change: q = m c ∆T + mH

You want to make ice tea in the summertime by brewing a pot of 1.0 L (1.0 kg) of tea at 372K, and cooling it to the drinking temperature of 275K. You have an unlimited supply of 50 g ice cubes at 263K. Determine the number of ice cubes to bring the ice tea to the perfect temperature. (cwater = 4.18 J·g-1·˚C-1, cice = 2.1 J·g-1·˚C-1, Hf (water) = 373 J/g) Solution
Hint Clear Info
Incorrect Attempts:
CHECK
cubes
qtea = -(qice cube + qcube phase change + qcube water)
Since the tea and ice cubes reach the same temperature, the heat lost in the tea equals the heat gained in the ice cube.

Let the total mass of ice cubes be 50n (where 'n' is the number of ice cubes, and each cube is 50g) Therefore (rounding up), 21 ice cubes are needed.

Specific Heat: Propane Fridge and Liquid Nitrogen

The following values are all used in the questions below.

boiling point N2 (l) = -196˚C
melting point N2 (s) = -210˚C
enthalpy of vaporization N2 (l), Hvap = 199 J/g
enthalpy of fusion N2 (l), Hfus = 25.7 J/g
specific heat N2 (g), c = 1.34 J/gK
specific heat N2 (l), c = 2.042 J/gK
specific heat N2 (s), c = 2 J/gK
boiling point NH3 (l) = -33˚C
enthalpy of vaporization NH3 (l), Hvap = 1,370 J/g
specific heat NH3 (l), c = 4.7 J/gK
specific heat NH3 (g), c = 1.64 J/gK

A propane fridge uses fire to cool things down (for real!). We want to freeze 250 grams of nitrogen gas at room temperature (25˚C) into a solid at -220˚C. Calculate the total heat that must be transferred (from the nitrogen gas by the refrigerator). The nitrogen is releasing heat (exothermic), and the refrigerator is gaining this energy (endothermic). Solution
q =
Hint Clear Info
Incorrect Attempts:
CHECK
J
Heat transferred out of a system is negative
The nitrogen gas must go through the 5 heat changes: Note that (g) → (l) and (l) → (s) is exothermic, which is -∆H...

Propane gas combustion is used to convert NH3 (l) → NH3 (g). The ammonia is gaining energy in this process, which is endothermic. The gaseous ammonia passes through cooling fins and condenses into liquid ammonia. From here, the liquid ammonia evaporates, which ______(I)______ energy in the food in the refrigerator, which is an ______(II)______ process for the ammonia. [2] Solution
Hint Clear Info
Incorrect Attempts:
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Hint Unavailable
...the liquid ammonia evaporates which removes energy from the food in the refrigerator, which is an endothermic process.

Assuming the ammonia is at room temperature (it isn't in real life) calculate the mass of liquid ammonia to freeze the nitrogen above, if the ammonia starts at -35˚C and ends up at 20˚C. Solution
m =
Hint Clear Info
Incorrect Attempts:
CHECK
g
Hint Unavailable
T1 = -35˚C, T2 = 20˚C... From before... qtotal = -142,452 J ... which becomes +142,452 J for the ammonia (endothermic, +∆H)...

Enthalpy

An endothermic reaction has a Solution
Endothermic reactions have positive enthalpy change, + ∆H.

The following reaction is exothermic. Solution
You can see this is exothermic (releases heat) because it has 802kJ of heat as a product on the righthand side of the equation.

Enthalpy and Stoichiometry

How much heat is released if 32.0 g of methane reacts with excess oxygen? Solution
q =
Hint Clear Info
Incorrect Attempts:
CHECK
kJ
Hint Unavailable
Determine the molecular weight of methane: 16 g/mol.
32.0 g of methane = 2 mol.
Given the exothermic equation, 1 mol of CH4 = -890kJ

Standard State Enthalpy of Formation

Explain why the enthalpy of formation, Hf of O2 (g) is zero. [1] Solution
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
The standard enthalpy of formation is the enthalpy to form 1.0 mol of a compound from its elements in their standard states. The diatomic form of gaseous oxygen, O2 (g), exists in the lowest energy form already. Since this is the lowest energy state and cannot be formed from lower energy constituent elements, then the enthalpy of formation starts at zero. Enthalpy of formation of all diatomic gases is zero.

Enthalpy

Given the molar heat of combustion of methane is -890 kJ/mol, calculate the enthalpy of reaction, Hrxn in the reaction given below. Solution
Hrxn =
Hint Clear Info
Incorrect Attempts:
CHECK
kJ
Hint Unavailable
This reaction is a combustion reaction, the enthalpy of combustion is the enthalpy of reaction, so enthalpy (H) is negative.

Each methane combustion is -890kJ/mol.
= 3mol(-890 kJ/mol)
= -2,670 kJ

Heat of Formation Hf˚

The enthalpy of formation of a compound is equal and opposite to the enthalpy of combustion. Solution
The enthalpy of reaction is the enthalpy of combustion, which is calculated using each of the enthalpies of formation of each compound.

Use the enthalpies of formation of each compound in the reaction to calculate the total enthalpy of reaction... using the equation:

Given the following information including the enthalpy of the reaction (combustion, Hc), calculate the enthalpy of formation, Hf˚ of sucrose C12H22O11 (s) Solution
Hf˚ =
Hint Clear Info
Incorrect Attempts:
CHECK
kJ/mol
Hint Unavailable

Calculating Enthalpy with Bond Energies and Hess' Law

Bond energy is the same magnitude and sign as enthalpy of formation. Solution
Bond energy is usually positive because this is the energy required to break the bonds. In the form C → A + B

Enthalpy of formation is usually negative because it is the energy released when the compound is made from its constituent elements. In the form A + B → C

Hess' law basically states that the change in energy in a chemical process does not depend on the number of steps to occur. Solution
Basically, the change in energy (enthalpy) of a target reaction does not depend on intermediate steps, and is the sum of the energy changes of all steps.

Given the reaction and the following bond energies, the enthalpy of formation of hydrofluoric acid would be calculated by which of the following generalized equations? Solution
These are bond energies given in the form C → A + B because the compound is breaking apart and the enthalpy is positive. Bond Energy Calculations are Reversed: Reactants - Products

Calculating Enthalpy with Bond Energies II

Given the reaction and the following bond energies, calculate the enthalpy of formation of hydrochloric acid. Solution
Hf =
Hint Clear Info
Incorrect Attempts:
CHECK
kJ/mol
Hint Unavailable
You can see these are bond energies given in the form C → A + B because the compound is breaking apart and the enthalpy is positive. (Bond Energy Calculations are Reversed: Reactants - Products)

Given the reaction and the following bond energies, calculate the enthalpy change for the formation of water. Solution
H =
Hint Clear Info
Incorrect Attempts:
CHECK
kJ/mol
Hint Unavailable
You can see these are bond energies given in the form C → A + B because the compound is breaking apart and the enthalpy is positive. (Bond Energy Calculations are Reversed: Reactants - Products)

ENTROPY

The Symbols

Explain the difference between ∆G, ∆H, ∆S and ∆G˚, ∆H˚, ∆S˚. [1] Solution
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
The degree (˚) symbol in ∆G˚, ∆H˚, and ∆S˚ means standard-state conditions: 1 atm, 298 K, and 1 mol/L (if aqueous).

If there are any non-standard-state conditions (1 atm, 298 K, and 1 mol/L), then the specific values of ∆G, ∆H, and ∆S must be calculated based on the non-standard-state reaction conditions.

The Equations

The equations for Gibbs free energy (G) and entropy (S) have the same format as enthalpy (H). Solution Video
True. And don't forget to multiply by the number of moles (n) if the individual formation equations get multiplied, or to switch the signs by multiplying by (-1) if the equations get reversed.

Incase you were dying to know, the generally accepted units are:
∆H˚fkJ/mol
∆H˚rxnkJ
∆S˚J/mol·K
∆S˚rxnJ/K
∆G˚kJ/mol
∆G˚rxnkJ

Gibbs Free Energy

What is Gibbs free energy? Solution Video
Gibbs free energy is the excess energy available from a reaction, used to do work. It is calculated by the entropy of a reaction minus the product of entropy and temperature. This is the work exchanged during a chemical reaction, between the system and surrounding. Gibbs free energy is at a minimum when the system (reaction) is at equilibrium.

Gibbs Free Energy ∆G

Match the different values of Gibbs free energy with their correct meaning. Solution Video
+ ∆G
- ∆G
∆G = 0
Spontaneous (Exergonic). The reaction is highly likely to occur because the conditions have enough energy.
The system is at Equilibrium. The forward and reverse reactions occur equally with the reverse reaction; no net change.
Non-spontaneous (Endergonic). At this temperature, the forward reaction will not occur, but the reverse reaction is more probable. There is not enough energy to drive the reaction forward (think endothermic).
Spontaneous (Exergonic) = - ∆G

Non-spontaneous (Endergonic) = + ∆G

Equilibrium, ∆G = 0 where ∆H = T∆S

Gibbs Free Energy ∆G and Spontaneity

Determine whether reactions with the following conditions will be spontaneous. Solution
-∆H, -∆S
+∆H, +∆S
-∆H, +∆S
+∆H, -∆S
Spontaneous (favorable) at any temperature
Non-spontaneous (unfavorable) at any temperature
Spontaneous at 'low' temperatures
Spontaneous at 'high' temperatures
The reactions that are spontaneous (favorable) at certain temperatures must use the Gibbs free energy equation to calculate the magnitude of temperature.

-∆H, +∆S → Spontaneous (favorable) at any temperature = -∆G
+∆H, -∆S → Non-spontaneous (unfavorable) at any temperature = +∆G
-∆H, -∆S → Spontaneous at 'low' temperatures
+∆H, +∆S → Spontaneous at 'high' temperatures

Laws of Thermodynamics

Know your thermodynamic laws. Fill in the blanks.

2nd Law of Thermodynamics: Entropy of the universe always ___________ during a spontaneous change. Solution
Entropy of the universe always increases during a spontaneous change.

3rd Law of Thermodynamics: Entropy of a pure crystalline solid is ___________ at ___________ kelvin. Solution
Entropy of a pure crystalline solid is 0 at 0 kelvin.

Entropy of Reaction

Calculate the entropy of reaction (∆S˚rxn) given the absolute entropies (∆S˚) in the table below, at SATP (298K, 1atm). Solution Video
S˚ Carbon graphite (s)5.6 J/mol·K
S˚ Oxygen, O2(g)205.1 J/mol·K
S˚ Carbon dioxide (g)213.7 J/mol·K
∆S˚rxn =
Hint Clear Info
Incorrect Attempts:
CHECK
J/K
Hint Unavailable
Remember the equation for entropy of reaction Plug the data into the equation... Therefore there is a decrease in entropy.

Entropy Situations

An increase in entropy is an increase in disorder where ∆S > 0, or (+∆S). Classify each of the following.

Which does not affect entropy? Solution Video
All of these affect entropy:
Physical phase (s, l, g, aq), Temperature, Pressure, Volume, and Moles.

Match the changes to the correct theoretical entropy change. Solution
Increase volume of a gas from 500mL to 2.0L
Increase pressure of an inert gas from 1atm to 2atm
Increase in entropy (+∆S)
Decrease in entropy (-∆S)
Increase in entropy:
- Increase volume
- Decrease pressure

(Basically if the molecules are spread further apart, occupying more space, then there is an increase in entropy. For example increasing temperature would cause volume to increase, increasing entropy...)

Which of the following phase changes is a theoretical decrease in entropy? Solution
Decrease in entropy (-∆S):

(higher entropy +∆S)      gas > liquid > solid      (lower entropy -∆S)
Decrease in entropy (-∆S) for soluble substances: aqueous > solid The entropies are:
  1. (s) → (aq) = +S
  2. (l) → (g) = +S
  3. (s) → (g) = +S
  4. (l) → (s) = -S

Match the changes to the correct theoretical entropy change. Solution
2H2O → 2H2 + O2
2O(g) → O2 (g)
Increase in entropy (+∆S)
Decrease in entropy (-∆S)
Increasing the number of moles in a reaction is an increase in entropy, +S.

Molecule A has a melting point at 10˚C, and molecule B has a melting point at 35˚C. At room temperature (25˚C), which molecule would have the lower entropy? Solution
Lower melting point = higher entropy.
Higher melting point = lower entropy.

The molecule that is has melted from a solid to a liquid has more kinetic motion in its molecules, would occupy a larger volume... and therefore would have a higher entropy.

The molecule that is still solid at room temperature would have the lower entropy. Molecule A melts first, leaving Molecule B still solid.

If a chemical reaction proceeds such that 2 moles are converted into 4 moles (A + B → 4C), in a container with fixed volume, at constant temperature, then determine the change in entropy. Solution
There would be no change in entropy over all

If the reaction occurs in a fixed volume container (cannot expand) then the increase in moles would cause an increase in pressure.
Individually the increase in moles would increase entropy, and the increase in pressure would decrease entropy. The net effect would cancel, so no net change in entropy.

Equal amounts of a saturated (animal) fat and unsaturated (plant) fat are at room temperature. Which fat would have the higher entropy? Solution
The fat that is melted into liquid would have a higher entropy than the fat that is still solid at room temperature. You should know that unsaturated fats (like olive oil) are liquid at room temperature, while saturated fats (like butter) are solid at room temperature. Therefore the unsaturated fat has the higher entropy.

Entropy (S)

Calculations with entropy must use what unit of temperature? Solution
Must use Kelvin (K)

Entropy: Spontaneous and Non-spontaneous

For a non-spontaneous reaction, calculate the temperature at which the reaction will become spontaneous, given ∆H˚ = 500 kJ, and ∆S˚ = 100 J/K. Solution
T =
Hint Clear Info
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K
Hint Unavailable
The (instantaneous) point at which a reaction changes from non-spontaneous to spontaneous is at equilibrium where ∆G = 0 Therefore it would take a huge amount of energy (high temperature, T = 5,000 K) to make this reaction spontaneous.

A Question with Enthalpy, Entropy, and Gibbs... The Whole Lot

Ethanol reacts with excess oxygen in a combustion reaction to produce carbon dioxide and water, both in gaseous states. Use the standard state (298 K) enthalpy of formation (Hf˚) and entropy (S˚) in the table to answer the questions.

∆Hf˚ (kJ/mol)∆S˚ (J/mol·K)
C2H6O (l)-278160
O2 (g)0205
CO2 (g)-394214
H2O (l)-28670

The balanced reaction equation is... Solution Video
The balanced reaction is:

Calculate ∆H˚rxn. Solution Video
∆H˚rxn =
Hint Clear Info
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kJ
Hint Unavailable
This is a lot of energy, it is exothermic, at 1.37 MJ.
(But as a comparison, high octane gasoline is over 5 MJ.)

Calculate ∆S˚rxn. Solution Video
∆S˚rxn =
Hint Clear Info
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kJ
Hint Unavailable

Determine if the reaction is spontaneous at standard state temperature, 25˚C. Solution Video
Hint Clear Info
∆G˚rxn = MJ , ∴ the reaction is:
Incorrect Attempts:
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Hint Unavailable
25˚C = 298K

Calculate ∆G to determine if spontaneous (make sure energy units are the same)... -∆G means the reaction, combustion of ethanol at room temperature, will be spontaneous.

Describe how diatomic gases used as reactants increases the available heat of the reaction greatly (more negative enthalpy). Solution Video H2, O2, F2, Br2, I2, N2, Cl2
The diatomic gases (X2) have enthalpy of formation equal to zero (∆H˚f = 0 kJ/mol). In the equation, the enthalpy of reactants becomes positive and reduces the "exothermic-ness" of the reaction, for example... The resulting ∆H˚rxn is largely negative and is highly exothermic. When combined with entropy in the Gibbs (∆G) equation, this results in a highly spontaneous reaction (-∆G).

In fact many rocket propellents use liquid oxygen, O2 (aka LOX) and liquid hydrogen H2 in the primary and upper stages of rocket launches.

Entropy of Fusion

Given the molar enthalpy of fusion and vaporization of ice and water below...

∆ Hfusion ice6 kJ/mol = 6,000 J/mol
∆ Hvaporization water40.7 kJ/mol = 40,700 J/mol

Determine the equation for change in entropy during a phase change (units J/K) to use in the next part below. Note that this is not the same as change in molar entropy (units J/mol·K). Solution Video
Determine the equation for entropy during a phase change... This occurs when the system is in equilibrium, therefore ∆ = 0... Multiply by number of moles...

If 496.47 g of ice melts with the same change in entropy as vaporizing an unknown amount of water, calculate the mass of the water that gets vaporized. Note the melting point of water is 0˚C and the boiling point is 100˚C. Solution Video
m =
Hint Clear Info
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g
Hint Unavailable
You should remember: Ice melts at 273 K, water vaporizes at 373 K, and water is 18 g/mol...

The question says they have the "same change in entropy" so set entropy of fusion equal to entropy of vaporization... The mass of the water that gets vaporized is 100 g.

Calculate the entropy of sublimation. (Note this is not molar entropy). Solution Video
∆Ssub =
Hint Clear Info
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J/K
Hint Unavailable
Sublimation is a phase change from (solid) to (gas). The entropy of the phase changes are additive...

Flashcards: Thermochemistry

What does the symbol q represent?
Heat transfer
A hot mug of coffee is placed in a refrigerator. If the mug is -100J, then what is the heat transfer of the fridge?
+100J
What type of energy is shown on an energy diagram of exothermic and endothermic reactions?
Potential energy
What is the difference between exothermic and endothermic reactions on an energy diagram?
In endothermic reactions reactants have less potential energy than the products, in exothermic reactions reactants have more potential energy than the products
Is vaporization an exothermic or endothermic process?
Endothermic. The process absorbs heat as the liquid turns into a gas, cooling down the surroundings.
What is adiabatic?
No heat transfer between the system and surroundings
What is isothermal?
Constant temperature between the system and surroundings
What is isobaric?
Constant pressure between the system and surroundings
Distinguish between an open, closed, isolated/insulated system.
Open: exchange energy and matter
Closed: exchange energy only
Isolated/insulated: No exchange of heat nor energy
What is specific heat?
The energy required to raise the temperature of one gram by 1˚C
What are the units for q, m, and T in the equation:
q = m c ∆T
q = Joules (J)
m = mass (g)
T = Kelvin (K) or Celsius (˚C)
What is the quantity, c in the equation:
q = m c ∆T
Specific heat capacity, with standard units of J/(g·˚C)
What is the difference in physical property that results from different materials having different specific heat (c) capacities?
The materials hold different amounts of heat energy (q) per unit of mass (m)
- ∆H indicates what type of reaction?
-∆H = Exothermic reaction

(+∆H = Endothermic reaction)
Is the reaction exothermic or endothermic?
Endothermic
What makes enthalpy of formation (H˚f) zero?
Enthalpy of formation (H˚f) is zero when the compound cannot be produced from lower energy building blocks, in other words if the energy of the compound is less than or equal to the energy of the starting constituents required to make the compound. An example the diatomic gases which are formed from standard state elements.
How is the enthalpy of reaction (∆Hr) calculated with Hess's Law?
Σ(∆H˚f of products) - Σ(∆H˚f of reactants)
If the decomposition of a reaction is +10kJ/mol, what would be the enthalpy change for the synthesis?
-10kJ/mol

Kinetics - Rates of Reactions

Rates of Reaction

In most reactions, the rate of reaction tends to ___________ over time. Solution
In most reactions, the rate of reaction tends to decrease over time (as the reactants get consumed).

Which (one) of the following does not affect the rate of a reaction? Solution
The number of moles would only affect the amount of product produced or the equilibrium, not the rate. It's the concentration (moles ÷ volume) of the reactants that affects rate...

Rates of Reaction: Rate Constant

Which of the following would affect the value of the rate constant, k? Solution
k only depends on the specific reaction, temperature, the presence of catalysts in the reaction, or the nature of the solvent(s).

k=Ae(-Ea/RT)

k = rate constant
A = frequency factor (constant that depends on temperature, frequency of collisions, orientation...)
e = mathematical quantity (e = 2.718...)
Ea = activation energy (in J/mol)
R = gas constant (from pV=nRT)
T = temperature (in K)

Rates of Reaction

Decreasing the surface area of NaOH(aq) or HCl(aq) will increase the rate of reaction. Solution NaOH(aq) + HCl(aq) ↔ NaCl(s) + H2O(l)
Surface area only affects heterogeneous reactions in which some of the reactants are in different phases from one another like dissolving and reacting a solid with an aqueous compound. In this example, the reactants are both aqueous so the rate of reaction will not depend on surface area.

Collision Theory

Chemical reactions occur when particles collide with sufficient energy and orientation for bonds to be broken, and new bonds formed. Collisions that don't have enough energy, do not result in a reaction. Increasing the temperature causes a higher frequency of collisions, resulting in reactions between particles. Solution
Increasing the temperature increases the kinetic energy (speed) of the reactant molecules. This would increase the energy of collision, as well as the frequency of collisions.

Catalysts

Two examples of common catalysts are enzyme proteins and platinum metal. Solution
Catalysts lower the energy required for a reaction to occur -- they increase the rate of reaction and increase the yield. Enzymes are catalysts in biology. Platinum is a common catalyst in chemistry.

Catalysts and Reaction Rate

Catalysts reduce the enthalpy of the reaction, allowing the reaction to proceed more to completion. Solution
Catalysts reduce the activation energy and not the enthalpy of a reaction. Activation energy is the energy required to rearrange the bonds in the molecule into a higher energy transition state. A catalyst reduces this energy, increasing the amount and rate of the reaction.

What is the order of a catalyst, such as an enzyme, in a rate equation? Solution
A catalyst reduces activation energy, increasing the amount and rate of the reaction...

However, this is tricky, the addition of a catalyst is all-or-none, meaning the concentration of the catalyst does not matter like it matters for the reactants. Since a catalyst does not get used/consumed in the reaction it is considered to have no affect and is ZEROTH order, [Catalyst]0.

Reaction Rates

Increasing the surface area of the reactants in which of the following reactions would increase the reaction rate? Solution
Increasing the surface area of the solid Sodium, Na(s) will increase the rate of reaction. For example, crushing the solid into a fine powder. Surface area affects all heterogeneous reactions, in which some of the reactants are in different phases from one another like dissolving and reacting a solid with an aqueous compound...

Determining Rates of Reaction with Molar Ratios

In the following reaction, if reactant 'A' gets used at a rate of 1.25 × 10-6 mol/(L·s), then at what rate is product 'D' formed? Solution 2A + 3B → C + 5D
Hint Clear Info
× 10
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Hint Unavailable
Use the ratios:

Orders of Reaction

The rate constant (k) affects the overall order of reaction. Solution
The rate constant (k) does not affect the order of reaction.

The overall order of reaction in the following rate law is Solution r = k[A]2[B]3[C]2
Hint Clear Info
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Hint Unavailable
Overall reaction order is found by adding the orders of reaction (superscripts) in the rate law equation.

For the following equation, the rate of the reaction is always r = k[A]2[B]3 Solution 2A + 3B → 2C
The orders of reaction (superscripts) in the rate law equation are determined empirically and are not always the same as the molar coefficients.

(However, if the reaction is elementary and the slow, rate-determining step, with no intermediates, then the rate equation would be based on the coefficients.)

Orders of Reaction

If the initial concentration of 'A' is doubled, while the other concentrations are kept constant, the overall reaction rate will increase by a factor of... Solution r = k[A]3[B]1
Hint Clear Info
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Hint Unavailable
Assuming the other concentrations are kept constant, the rate of the reaction will increase by Rate Factor:
= (concentration multiple)order
= (2)3
= 8

If the order of reactant 'A' is two, then tripling the concentration of [A] would increase the overall reaction rate by how much? Solution r = k[A]2[B]3
Hint Clear Info
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Hint Unavailable
[concentration]order

= [A]2
= [3]2
= 9

Determining Reaction Rate Directly

In the complete combustion of methane with excess oxygen, if 88.0 g of CO2(g) is produced in 32.4 s, what is the rate of the reaction? Solution CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
Hint Clear Info
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mol/s
Hint Unavailable
= 88g ÷ 44g/mol ÷ 32.4s
= 0.062 mol/s

Rates of Reaction

The rate law equation can be predicted from the stoichiometry (coefficients) in the reaction equation. Solution
The rate law must always be calculated experimentally. Sometimes the rate law is consistent with the stoichiometry, but this would be a coincidence because often the rate law is usually not consistent with the stoichiometry. (EXCEPT FOR THE SLOW, RATE-DETERMINING STEP, IF THERE ARE NO INTERMEDIATES...)

Rate Determining Step

The rate determining step in a reaction is always the slowest step in the theorized reaction mechanism. Solution
The slowest reaction within the overall reaction is often many orders of magnitude slower and is the main determinant of the reaction speed, especially of all other sub-reactions occur very quickly.

Orders of Reaction

When [A] is doubled, the rate increases by a factor of 8.
When [B] is doubled, the rate does not change.

A + 2B → 3C + D

Determine the rate equation given the information for the reaction above. Solution
rate =

¹

²

³

Incorrect Attempts:
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Hint Unavailable
Rate factor increase = (multiple)Order

r = k[A]3[B]0

r = k[A]3

Determine (the concentration of) [A] in the reaction above given the values in the table. Solution
Rate = 0.5 × 10-6 mol/(L·s)
k = 4.0 × 10-5 L2/(mol2·s)
[B] = 0.50 mol/L
[A] =
Hint Clear Info
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mol/L
Hint Unavailable
Notice that we don't need [B]... this is called a 'red herring' in a question...

Propose an equation for the rate (r) of the rate-determining step in the slow-step of the reaction mechanism. Solution
Given the overall reaction: A + 2B → 3C + D The rate-determining step is the slowest step out of all the different steps in the reaction mechanism.
Normally we go from the reaction to determine the order... But for the slow-step of the reaction mechanism, we can say that the order (3) is the coefficient on 'A'... 3A...
Since r = k[A]3, a rate determining step would be: 3A → product(s) (We are not concerned with what all the other reaction mechanisms might be. Reaction mechanisms come from some reactions that cannot be completed in a single step like an elementary reaction, so sometimes overall reactions occur through several smaller 'sub-steps' or reaction mechanism steps.)

Rate-Determining Step

If two moles of a molecule or two different molecules are involved in the rate-determining step in the reaction mechanism, then the overall reaction is considered second order. Solution
THIS ONLY WORKS FOR THE RATE-DETERMINING STEP. (If there aren't any intermediates)

r = k[A]2, the rate determining step would be: 2A → product(s)

or

r = k[A]1[B]1, the rate determining step would be: 1A + 1B → product(s)

Rates of Reaction

Rate can be calculated with the following... Solution
For example, the rate can be in terms of concentration , volume , or mass ...

In the reaction below, AB decomposes from 5.5 mol/L at 15 seconds, to 0.83 mol/L at 60 seconds. Calculate the average rate of decomposition of AB. Solution AB → C + D
ravg =
Hint Clear Info
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mol/L·s
Hint Unavailable
Average rate is like 'slope' of the change in concentration over the change in time...

Determining Order of Reactions Empirically

The table contains the experimental information for the reaction given below, at a certain temperature.

3A + B + C → 2D + E
TestInitial [A] (mol/L)Initial [B] (mol/L)Initial [C] (mol/L)Rate of Production of E (mol/(L·s))
10.40.20.30.75 × 10-2
20.80.20.33.0 × 10-2
30.40.40.31.5 × 10-2
40.40.20.63.0 × 10-2

Given the experimental information, calculate the rate law equation and make a general equation for the rate-determining step. Solution
rate =

¹

²

³

Incorrect Attempts:
CHECK
Hint Unavailable
Here we are calculating the rate law equation experimentally... as we should. Rate Factor:
= (Concentration Multiple)Order
Calculate the order of [A] using trials 1 & 2:
[Concentration] 0.4 → 0.8 = ×2
Rate 0.75 → 3.0 = ×4 Rate Factor:
= (Concentration Multiple)Order
4 = 2Order
Order = 2
Calculate the order of [B] using trials 1 & 3:
[Concentration] 0.2 → 0.4 = ×2
Rate 0.75 → 1.5 = ×2 Rate Factor:
= (Concentration Multiple)Order
2 = 2Order
Order = 1
Calculate the order of [C] using trials 1 & 4:
[Concentration] 0.3 → 0.6 = ×2
Rate 0.75 → 3.0 = ×4 Rate Factor:
= (Concentration Multiple)Order
4 = 2Order
Order = 2


Rate law equation: rate = k[A]2[B]1[C]2

Rate-determining step: 2A + 1B + 2C → Product(s)

Calculate the rate constant for this reaction. Solution
k =
Hint Clear Info
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Hint Unavailable
Use any one of the tests, and substitute it into the rate law equation you determined from before. I will use the data from test 1...

Determine the rate of production given the initial concentrations below... Solution
ReactantInitial Concentration
[A]0.1 mol/L
[B]0.2 mol/L
[C]0.3 mol/L
r =
Hint Clear Info
× 10
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mol/L·s
Hint Unavailable
Since you already calculate the rate constant, just substitute the given concentrations into the rate equation.

Determining Order of Reaction Graphically

Given the graphs of (concentration over time of) production and decomposition, determine the order of reaction.

Solution
If the graph of [Concentration] Vs. Time is LINEAR, then the reaction is 0th, Zeroth order.

Solution
If the graph of the log or ln of concentration, Log[Concentration] Vs. Time or Ln[Concentration] Vs. Time is LINEAR, then the reaction is 1st, First order.

Solution
If the graph of the reciprocal of concentration, 1/[Concentration] Vs. Time is LINEAR, then the reaction is 2nd, Second order.

Given the following information, determine the overall order of the reaction. Solution
Time (s)[Concentration] (mol/L)
10 1.0
20 0.50
30 0.33
To determine the order, sketch the three following graphs.

Look for the graph that is LINEAR. This is the order of the reaction:

0th, Zeroth order: [Concentration] Vs. Time (Regular)

1st, First order: Log[Concentration] Vs. Time (Log)... or Ln[Concentration] Vs. Time

= 2nd, Second order: 1/[Concentration] Vs. Time (Reciprocal)
↑ This is the LINEAR graph, therefore the reaction is 2nd order.

Which of the following is not associated with the rate of reaction? Solution
All of the above are associated with the rate Note that mol/L·s is the same as once rearranged.

The Varying Units of Rate Constants, k

If the units for a rate of reaction are mol/(L·s) and the units of concentration are mol/L, what would the units of k be in the following reaction? Solution rate = k[A]2[B]1
Try substituting to see what happens to the units

Rate Determining Step

Given the overall reaction and the mechanism steps...

Which of the following is classified as a reaction intermediate? Solution
Reaction intermediates do not appear in the overall, net reaction. Therefore 'D' is a reaction intermediate because it gets canceled between step 2 and 3. Note that the intermediate is never included in the rate law equation.

The reaction, is an elementary reaction. Solution
An elementary reaction goes directly from reactants to products, with no intermediate mechanism steps. However, steps 1-3 are considered elementary reaction steps...

Determine the rate law equation based on the rate-determining step. Solution
rate =

¹

²

³

Incorrect Attempts:
CHECK
Hint Unavailable
Since 'D' is an intermediate it is not in the rate law equation... Rate Law = k[B][D] The rate determining step is based on the slow step, where the reactant coefficients of the reaction are the rate law orders. But wait there's an exception! ...

... If the slow step contains intermediates, then all the reactants in the fast step that contains the slow-step intermediate are included in the rate law... ∴ rate = k[B]2[C]1 Explanation: step 2 is 'so fast' that adding more [C] will instantly turn into [D] and is 'like adding' more [D] (even though [D] is an intermediate) which is what the slow step is 'waiting for'. Basically if [C] is doubled then [D] will quickly double. [D] produced in step 2 is limiting and dependent for step 3!

Integrated Rate Law, First Order

Given the integrated rate law for first order reactions, where [A]t is the concentration at time 't', k is the rate constant, and ln[A]0 is the initial concentration of the reactant.

ln[A]t = -kt + ln[A]0

State what each of the quantities represents on a cartesian plane (graph). Solution Video
QuantityGraph Value
ln[A]t
-k
t
ln[A]0
Based on the linear equation: y = mx + b...
QuantityGraph Value
ln[A]ty-value (output, dependent)
-kslope, m
tx-value (input, independent)
ln[A]0y-intercept, b

Why is the slope of this graph decreasing? Solution
The slope (-k) is decreasing because the y-value, the reactant, ln[A]t is decreasing over time as it is consumed in the reaction.

The pharmacokinetics of ibuprofen shows first-order kinetics with a serum (blood) half life of approximately 2 hours. Based on a 400 mg dose, the serum concentration of ibuprofen is 30 mg/L. If the rate constant, k equals 0.3466 hr-1, determine the time for one dose to reach 1 mg/L in the blood. [This uses numbers from real lab tests] Solution Video
t =
Hint Clear Info
Incorrect Attempts:
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hours
Hint Unavailable
Given: initial concentration [A]0 = 30 mg/L, final concentration [A]t = 1 mg/L, and the rate constant k = 0.3466 hr-1...

(Notice we don't need the 2 hour half-life or the 400 mg dose.)

Rearrange the first order integrated rate law for time, then sub in... Therefore it takes approximately 9.81 hours for the serum concentration of ibuprofen to dissipate from 30 mg/L to 1 mg/L.

Integrated Rate Law, First Order Example

Determine an equation for time in a half-life equation in terms of the rate constant, k. Given that for half life, the final concentration [A]t equals half the initial concentration [A]0: Solution
t =
Hint Clear Info
━━━
Incorrect Attempts:
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Hint Unavailable
Sub this into the first order integrated rate law equation for [A]t and [A]0...

Integrated Rate Law, First Order Example

Half-life equations mostly follow first order kinetics. Given:

ln[A]t = -kt + ln[A]0

A radioisotope decays in 145.2 days. Calculate the rate constant, k. Solution
k =
Hint Clear Info
Incorrect Attempts:
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days-1
Hint Unavailable
Use the equation for time in a half-life equation, in terms of the rate constant, k

If 100.0 g of this isotope decayed over 15 years, calculate the final amount remaining... Solution
Amount =
Hint Clear Info
× 10
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grams
Hint Unavailable
The equation works for concentration as well as masses...
Note that 15 years = 5475 days...

Integrated Rate Law, Second Order

Given the integrated rate law for second order reactions, where [A]t is the concentration at time 't', k is the rate constant, and ln[A]0 is the initial concentration of the reactant.

Based on the given integrated rate law for second order reactions, what quantity is represented by the slope? Solution
The slope is 'k'

Based on the given integrated rate law for second order reactions, what quantity is represented by the slope? What quantity is represent by the y-intercept? Solution
The slope is 'k'

The y-intercept is

If a particular insecticide follows second order kinetics and has a rate law constant (k) of 0.555 M-1s-1, determine the initial concentration if the concentration after 10 minutes is 0.00298 M. Solution
[A]0 =
Hint Clear Info
Incorrect Attempts:
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M
Hint Unavailable
Don't forget to convert 10 minutes to 600 seconds. Therefore the initial concentration, [A]0 is 0.389 mol/L

Flashcards: Kinetics

What factors affect the rate of a reaction?
Concentration, surface area, temperature, pressure, catalysts, and solvent type.
Under what conditions can the reaction coefficients be used as the orders in the rate law equation?
Only if the coefficients are from the elementary step (no intermediates) and it is the slow, rate determining step.
Are reactants from fast steps sometimes included in the rate law equation?
Yes! If there are several mechanism steps that make up the overall reaction and the slow step contains intermediates, then the fast reaction with that intermediate has all its reactants in the rate equation.
Does increasing the amount of moles affect reaction rate?
No
What is a reaction intermediate?
Reaction intermediates do not appear in the overall, net reaction
Are intermediates included in the rate law equation?
No, never
What factors affect the value of the rate constant (k) in the rate equation?
k only depends on temperature, presence of a catalyst, or the nature of the solvent.
What do catalysts change in a reaction?
The activation energy, Ea
If the initial concentration of reactant A is tripled, what will happen to the rate?
r = k[A]3[B]1
The overall reaction rate will increase by a factor of 27

( = [3]3 = 27)
What is the overall order of the reaction?

r = k[A][B]2[C]2
5
If the initial concentration of reactant A is doubled, what will happen to the rate?
r = k[A]0[B]1[C]2
Nothing happens with changes to a zero order reactant.
What is the rate-determining step?
The rate determining step in a reaction is always the slowest step in the theorized reaction mechanism.
Is the activation energy for the forward reaction equal in magnitude to the activation energy for the reverse of the same reaction?
No, the magnitudes are different, depending on the potential energies of the reactants, products, and intermediates.

Chemical Systems and Equilibrium

Equilibrium

For the reaction equation, determine the equilibrium constant equation assuming all reactants and products are aqueous. Interpret what a low Keq value indicates. Solution Video
The equilibrium constant equation is: A low Keq value indicates that at equilibrium, the concentration of the reactants [A] and [B] are greater than the concentration of the products [C] and [D]. This means that the reaction will not proceed to produce much products.

When equilibrium is reached in a chemical reaction, the forward and reverse reactions have stopped. Solution Video
The forward and reverse reactions are always occurring, even at equilibrium - when the forward rate equals the reverse rate.

When the ion product (Q) equals Kc, or Keq, or Ksp, or Kp, the reaction is at equilibrium and can be summarized with Gibbs free energy... Solution ∆G = 0
Gibbs free energy (when ∆G = 0) indicates the reaction is at equilibrium, similar to Q = K ...

Equilibrium Constant

A high Keq value indicates Solution Video
A high value indicates that at equilibrium the concentration, [] compares like this: [products] > [reactants]... E.g.)

Equilibrium Constant Expression

Determine the correct keq equation for the following reaction. Solution Video
The keq equation is made of products over the reactants, and the concentration is raised to the exponent of the coefficient in front.

Equilibrium Constant Expression for Heterogeneous (2 or More Phase) Systems

Determine the correct keq equation for the following reaction. Solution Video
Pure solids and liquids/solvents do not appear in equilibrium constant expressions because the concentration of these things does not even make sense.

Equilibrium Constant Forward and Reverse

Determine the equilibrium constant, keq for the reverse of the following reaction. Solution
Hint Clear Info
Incorrect Attempts:
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Hint Unavailable
Write the keq equations for the forward and for the reverse of the reaction and notice the reciprocal relationship.

Equilibrium and Catalysts

Catalysts shift the equilibrium position in a reaction to increase the amount of products. Solution
Catalysts do not move the equilibrium, they only change the activation energy and the rate of reaction.

Le Châtelier’s Principle with Gases and Aqueous

Determine the effect of increasing the pressure in the system by a reasonable amount. Solution
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
Since solids do not respond to typical changes in pressure (nor do liquids) because they have a constant volume, the reaction will not shift to the right, in fact it will shift to the left. Only consider the gaseous molecules that can change volume...

Which three of the following will shift the reaction to the left? Solution
To shift the reaction to the left...
  • Increase temperature, add heat
  • Decrease pressure (by increasing volume)
  • Remove [H2] or [O2]
  • Increase [H2O]

Determine the change that would increase the solubility of rubidium fluoride, RbF. Solution
  • Since energy is a product this is an exothermic reaction. You can drive exothermic reactions to the right, increasing solubility, by removing energy (decreasing temperature).
  • Adding more reactant will not increase the solubility (molarity) of the reactant.
  • Pressure does not affect solid and aqueous.
  • Adding more water or shaking the solution would increase the rate of dissolving the solid, but would not increase the solubility (molarity) of the reactant, which is based on the ksp magnitude.

Different 'k' Constants

Describe some of the similarities and differences between Keq, Ksp, Kc, and Kp? Solution
With calculations...
  • They are all calculated with [products] ÷ [reactants], and raised to the power of the coefficients
  • None use solids or liquids in the equations
Generally...
  • Keq is the general equilibrium constant used for gases or aqueous ions...
  • Kc is also the general equilibrium constant used for gases or aqueous ions...


  • Ksp is used only with concentrations for solubility of aqueous ions, and uses brackets in the equation
  • Kp is used only for pressure of gases, and uses parenthesis in the equation

Given the equation below where R is the gas constant (0.0821 L·atm/mol·K), T is temperature, and n is the amount of moles, is it possible for kp to equal kc? If not explain why, if so provide an example in support. Solution
Yes it is possible for them to be equal. Consider the example where the moles on the left side is 2 and mols on the right side is 2... So, Here we can see they are the same, but often they are different.

Equilibrium Constant

Which of the following will affect the equilibrium, Ksp? Solution
  1. Temperature
  2. Catalysts
  3. Concentration
Only temperature affects ksp, keq

Equilibrium Calculations with ICE

Given the reaction equation below and the following initial concentrations, determine the concentration of NO(g), once equilibrium is reached after adding 0.7 mol/L of NO(g) to the system. Solution
[ClNO2][NO][NO2][ClNO]
0.8 mol/L0.1 mol/L0.2 mol/L0.3 mol/L
[NO] =
Hint Clear Info
Incorrect Attempts:
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M
Hint Unavailable

The equation below can be used to determine when the 'x' value can be neglected, when it is added (or subtracted) from the initial amount. Solution
Use this to simplify the equilibrium amount before plugging into Kc, Keq equations...

We are able to do this because a low Kc or Keq means the reaction has low amount of products at equilibrium so there is a small enough change in 'x' for the reactants or products, and can be neglected if it is added or subtracted from the initial amount... see next question for an example of this...

Given the reverse reaction and the following initial concentrations, determine the concentration of the products at equilibrium. Solution
[NO2][ClNO][ClNO2][NO]
0.1 mol/L0.3 mol/L0 mol/L0 mol/L
Hint Clear Info
[ClNO2(g)] = M [NO(g)] = M
Incorrect Attempts:
CHECK
Hint Unavailable
With a low keq (0.00083) first check if we can neglect 'x'... When the ratio is over 100 we can neglect 'x' when it is added or subtracted.
But cannot neglect the lone 'x's...
[NO2][ClNO][ClNO2][NO]
I0.1 mol/L0.3 mol/L0 mol/L0 mol/L
C-x-x+x+x
E0.1 - x 0.3 - x xx
Set up the Keq equation... Therefore there is 0.17 M of both ClNO2 (g) and NO(g).

Understanding Solubility Product Constant Ksp

Given the following reaction...

Determine the ksp formula. Solution
Remember that solids are not used in Ksp equation because the concentration of a solid does not make sense.

What would a low Ksp value mean? Solution
The reaction does not proceed significantly to the right, since, A low Ksp means the [reactants] > [products]

For example, if [reactants] is over 100 times greater than [products]...

You are going to calculate the ksp of a solution of calcium phosphate, Ca3(PO4)2 in your lab. Eventually you evaporate 10 L of the solution until a powder is left, which weighs 3.53 × 10 -4 grams. You got this! Solution
ksp =
Hint Clear Info
× 10
Incorrect Attempts:
CHECK
M
Hint Unavailable
Ca3(PO4)2 is 309.9 g/mol
Moles: The molar solubility (concentration) is Make an ice table,
Ca3(PO4)2 (s)3Ca2+(aq)2PO4 (aq)3-
I--0 mol/L0 mol/L
C--+ 3x+ 2x
E-- 3x2x
Calculate ksp, where x = 1.14 × 10-7 M

Molar Solubility

Given the general equation below...

If the molar solubility of the compound XaYb (s) is 0.1 M, determine the solubility of the ion products in terms of a and b. Solution
0.1 M XaYb (s) would dissociate into, X(aq): 0.1a M And, Y(aq): 0.1b M

Starting from zero products, can the molar solubility of the products X(aq) and Y(aq) be different from molar solubility of XaYb (s) times the coefficient 'a' or 'b'? Solution
No, the molar solubility would always be 0.1a M of X(aq) and 0.1b M of Y(aq) because the reaction equation would always have a coefficient of one, so like 1XaYb (s)...

Solubility Product Constant Ksp Calculation

Given the following equation, determine the solubility of calcium hydroxide in water by determining the concentration of the calcium ion at equilibrium. Solution
[Ca(OH)2] =
Hint Clear Info
× 10
Incorrect Attempts:
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M
Hint Unavailable
Set up the ICE table for Ksp just like you are used to for keq...
Ca(OH)2Ca2+2OH-
initialn/a00
changen/a+x+2x
equilibriumn/ax2x
Remember Ksp does not include solids because the concentration of a solid does not make sense.

Temperature and Ksp

Nitrate salts are typically highly soluble and can be assumed to dissociate completely. Solid silver nitrate, AgNO3 is dissolved until saturation in water at 1 atm at the three different temperatures in the test tubes below.

Tube A, 20˚CTube B, 60˚CTube C, 100˚C
12.7 M25.9 M43.1 M

Calculate the Ksp at each temperature. Solution
Hint Clear Info
Tube A, 20˚CTube B, 60˚CTube C, 100˚C
12.7 M25.9 M43.1 M
Ksp = Ksp = Ksp =
Incorrect Attempts:
CHECK
Hint Unavailable
(Only temperature can affect Ksp...)
At 20˚C... At 60˚C... At 100˚C...

Calculate the percent increase in Ksp from 20˚C → 100˚C. Solution
Hint Clear Info
Incorrect Attempts:
CHECK
%
Hint Unavailable
Percent increase is,

Determine Ksp Given Equilibrium Concentration

It is possible to calculate the solubility product constant, Ksp given only the solubility of a salt at a certain temperature. Solution
For example with copper(II) fluoride, the equation is If the solubility at a certain temperature is 0.05M, then this is the concentration at equilibrium of the copper ions and 2 times the fluoride ions.

Create an ICE table and the Ksp formula to calculate...

Determine the Ksp of CuF2 if the equilibrium concentration (at a certain extreme temperature) of F-(aq) is 0.002 mol/L and the reaction starts with 100% reactants. Solution
Ksp =
Hint Clear Info
× 10
Incorrect Attempts:
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M
Hint Unavailable
CuF2Cu2+2F-
initialn/a00
changen/a+x+2x
equilibriumn/ax2x
At equilibrium, the [F-] = 2x = 0.002 mol/L
x = 0.001 mol/L
Solids are not included in Ksp equations... Ksp = [Cu2+]1[F-]2
= [x]1[2(x)]2
= [0.001]1[2(0.001)]2
= 4.0 × 10-9 mol/L

Determine Ion Concentration at Equilibrium Given Ksp

Given the Ksp below, the molar solubility of CaF2 (s) is 0.40 M, so [F-] = 0.40 M, and [Ca2+] = 9.25 × 10-8 M. Solution
CaF2Ca2+2F-
initialn/a00
changen/a+x+2x
equilibriumn/ax2x
Do not include solids in k constant equation...
CaF2Ca2+2F-
initialn/a00
changen/a+x+2x
equilibriumn/a0.0021 M2(0.0021 M) = 0.0042 M
False, [F-] does not equal 0.40 M, and [Ca2+] does not equal 9.25 × 10-8 M.

Given the solubility product constant (Ksp) of calcium phosphate, Ca3(PO4)2 is 2.1 × 10-33, determine the concentration of phosphate, PO4 in the calcium fluoride solution at equilibrium. Solution
[PO4] =
Hint Clear Info
× 10
Incorrect Attempts:
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M
Hint Unavailable
You already calculated the concentration of calcium is 0.0021 M at equilibrium. Use this as the initial amount for the dissociation of calcium phosphate.
Ca3(PO4)23Ca2+2PO43-
initialn/a0.0021 M0 M
changen/a+ 3x+ 2x
equilibriumn/a0.0021 M + 3x2x
Hopefully this made sense to you, you used the solubility product constant of calcium phosphate and neglected the change in x for the calcium.

Gases (With and Without Partial Pressures)

The breakdown of ammonia is the reverse of the Haber process. Calculate the reaction quotient, q for the breakdown of ammonia under certain conditions...

Starting with 1.2 mol ammonia, 3.2 mol nitrogen, and 4.5 mol hydrogen, in a 2L container at a certain temperature. Solution
q =
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
Don't need to calculate the partial pressures here... the reaction quotient, q just uses the molarity of the gas (mol/L)... Calculate reaction quotient, q... (Then you would compare this value with k to see where the reaction is compared to equilibrium, hence if shifts to left or right...)

If the total pressure is 7.5 atm at a different temperature, use mole fractions to calculate partial pressure to calculate the new reaction quotient. Solution
qp =
Hint Clear Info
Incorrect Attempts:
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Hint Unavailable
(The partial pressure is the pressure that a gas in the mixture would exert if it was the only gas in the container.)

First calculate the mole fraction of each of the gases... Then calculate the partial pressures.. Just plug the 'partial pressures' of the gases right into the reaction quotient equation, q. Make sure to include "P" for partial pressure in your equation... (Then you would compare this value with k to see where the reaction is compared to equilibrium, hence if shifts to left or right...)

If the equilibrium constant (Kp) is 9,000 then calculate the partial pressures at equilibrium starting with 1 atm of ammonia. Solution
P:
Hint Clear Info
NH3 = N2 = H2 =
Incorrect Attempts:
CHECK
atm
Hint Unavailable
Since Q << K, then the reaction will shift to the right...
Use an ice table,
2NH3 (g)N2 (g)3H2 (g)
I (Initial)1 atm00
C (Change)- 2x+ x+ 3x
E (Equilibrium)1 - 2xx3x
Calculate the change given the equilibrium constant (Kp) is 9,000
Since the ratio of the lowest partial pressure to 'k' is less than 100, we cannot neglect where 'x'... Since we start with 1 atm, we can neglect the outliers -37 and 36...
Average and round the middle values... x = 0.5

Therefore at equilibrium there is:
  1. ammonia: 1 - 2(0.5) = 0 atm
  2. nitrogen: 0.5 atm
  3. hydrogen: 3(0.5) = 1.5 atm

Solubility Product Constant Ksp and Ion Product Constant Qsp

If the solution is not at equilibrium, then Qsp is used instead of Ksp. Solution
True

If Ksp = Qsp then Solution
The reaction is at equilibrium between the reactants and products.

No precipitate will form.

When Ksp > Qsp, some more of the compound would be able to dissociate into solution. Solution Video
Ksp is a constant, while Qsp is a 'gauge' of the ion concentrations before equilibrium is reached. So if Qsp is higher than Ksp, too many ions are present and some precipitate will form. Conversely, if Qsp is lower than Ksp, this means there is still room for ions to dissolve and more of the compound will dissociate.

Precipitate Formation

The most abundant ions in hard tap water are calcium, Ca2+ and magnesium, Mg2+. Given the Ksp values of various compounds, determine which would make the best water softener, in other words, which would precipitate the calcium and magnesium ions. Solution
KspCa2+Mg2+
CO32-4 × 10-96.8 × 10-6
F-3.5 × 10-115.2 × 10-11
PO43-2.1 × 10-331 × 10-24
OH-5 × 10-65.6 × 10-12
ClO3-> 100> 100
Water softeners replace the calcium and magnesium ions with much more soluble lithium Li+, sodium Na+, and potassium K+ ions.

The lowest Ksp precipitates the calcium and magnesium out of solution - and is the best water softener. So the phosphate salt is the best water softener. K3PO4

Precipitate Formation

Mixing 0.15 L of a 0.02 M solution of lithium carbonate with 0.02L of 0.1 M solution of zinc fluoride...

Determine the concentration of zinc ions and carbonate ions in the mixed solution. Solution
Hint Clear Info
[Zn+] = [CO32-] =
Incorrect Attempts:
CHECK
M
Hint Unavailable
Be careful - when the solutions are mixed the volume increases and the concentration of the ions decreases.

Concentration of zinc ions, Concentration of carbonate ions,

Given the solubility product constant of zinc carbonate, ZnCO3(s) is 1.19 × 10-10, determine whether a precipitate of zinc carbonate will form in the mixture. Solution
Hint Clear Info
Qsp =× 10
Will a precipitate form?
Incorrect Attempts:
CHECK
Hint Unavailable
A precipitate forms when Qsp > Ksp
ZnCO3 (s)Zn2+(aq)CO32-(aq)
I (Initial)--0 M0 M
C (Change)--+ x+ x
E (Equilibrium)--xx
Calculate Q... Since Qsp > Ksp, then yes a precipitate will form.

All About Precipitates

A solution contains an initial 0.001 M concentration of fluoride and sulfate ions. Good luck!

When strontium chlorate, Sr(ClO3)2 - which is considered very soluble - is added to the solution, determine the salt that will precipitate first. Show your work. Solution
Adding the strontium chlorate, Sr(ClO3)2 is basically like adding [Sr2+] ...

You can calculate the concentration [Sr2+] at equilibrium using the ksp. The precipitate forms when the ion product (Q) is ≥ Ksp. You know the lower (concentration of) [Sr2+] at equilibrium will precipitate first.
SrF2(s)Sr2+(aq)2 F-(aq)
I (Initial)--0 M0.001 M
C (Change)--+ x+ 2x
E (Equilibrium)--x0.001 + 2x
SrSO4(s)Sr2+(aq)SO42-(aq)
I (Initial)--0 M0.001 M
C (Change)--+ x+ x
E (Equilibrium)--x0.001 + x

Since the ratio of initial concentration 0.001M to the ksp is greater than 100, you can neglect wherever 'x' is added...
At equilibrium, since the (concentration of) [Sr2+] from SrSO4 is lower than the (concentration of) [Sr2+] from SrF2, the SrF2 will start to precipitate first.

Calculate the molarity of strontium chlorate, Sr(ClO3)2 when the first precipitate starts to precipitate. Solution
[Sr(ClO3)2] =
Hint Clear Info
× 10
Incorrect Attempts:
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mol/L
Hint Unavailable
Since you already solved the concentration of strontium ions when the first precipitate forms... And the molar ratio of strontium ions to strontium chlorate is 1 Sr2+ : 1 Sr(ClO3)2, then the molarity of strontium chlorate is the same... (Aside: the molarity of the chlorate ions would be twice this, 2 × 3.4 × 10-4 = 6.8 × 10-4).

Now that you know the order of precipitation, calculate the concentration of sulfate, SO42- ions when strontium fluoride, SrF2 begins to precipitate. Solution
[SO42-] =
Hint Clear Info
× 10
Incorrect Attempts:
CHECK
mol/L
Hint Unavailable
You already know the SrSO4 precipitates first → then the SrF2 begins to precipitate...

You already calculated when the strontium fluoride, SrF2 begins to precipitate, the concentration of [Sr2+] ions at this point is [Sr2+] = 4.3 × 10-3 M Now use this ↑ concentration of [Sr2+] ions in the ksp equation for strontium sulfate, SrSO4...

The Common Ion

If 80mL of 0.6M MgBr2 is mixed with 100mL of 0.7M LiBr, find the total concentration of the bromide (Br-) ions, both salts are considered very soluble. Solution
[Br-] =
Hint Clear Info
Incorrect Attempts:
CHECK
mol/L
Hint Unavailable

The Common Ion Effect

Adding some solid Pb(NO3)2 to a saturated solution of PbCrO4 at equilibrium will precipitate some PbCrO4 and the [CrO42-] will decrease. Solution
Lead (Pb2+) is the common ion... Nitrate is very soluble and so many more lead (Pb2+) ions will dissolve into solution, causing the reaction to shift to the left because of Le Chatelier's principle. Basically, since temperature (and hence Ksp) is constant, increasing the concentration of lead ions will decrease the [CrO42-] (concentration of chromate ions) causing some PbCrO4 to precipitate.

Lead chromate, PbCrO4 would be most soluble in a solution containing... Solution
Any solutions already containing either lead, Pb2+ or chromate, CrO42- ions would make the lead chromate, PbCrO4 less soluble.

Lead nitrate, Pb(NO3)2 would be least soluble in a solution containing... Solution
Common ion will reduce the solubility of lead nitrate, Pb(NO3)2. The sodium nitrate is extremely soluble and will dissociate many nitrate, NO3- ions into solution. Even more than the 2 mols from barium nitrate...

The Common Ion Effect

The solubility product constant (Ksp) of calcium sulfate and silver sulfate are given at 25˚C.

Calculate the solubility of Ag2SO4 in pure water. Solution
Hint Clear Info
× 10
Incorrect Attempts:
CHECK
M
Hint Unavailable
Make an ICE table,
Ag2SO4 (s)2Ag+(aq)SO42-(aq)
I (Initial)--0 M0 M
C (Change)--+ 2x+ x
E (Equilibrium)--2xx
Sub the molar solubility at equilibrium, 'x' into the solubility product constant equation... This is the (molar) solubility of Ag2SO4 in pure water.

Calculate the solubility of CaSO4 in a saturated solution of Ag2SO4 (s) (assuming excess silver sulfate). Solution
Hint Clear Info
× 10
Incorrect Attempts:
CHECK
M
Hint Unavailable
Make an ICE table, starting with 1.4 × 10-2 M SO42- because it is a saturated solution...
CaSO4 (s)Ca2+(aq)SO42-(aq)
I (Initial)--0 M1.4 × 10-2 M
C (Change)--+ x1.4 × 10-2 M + x
E (Equilibrium)--x1.4 × 10-2 + x
IMPORTANT! - first see if you can neglect 'x', if the ratio of the molar solubility to the Ksp is greater than 100... Since the ratio is > 100, then you can neglect 'x' because it is considered a small or negligible change compared to the molar solubility 1.4 × 10-2...
CaSO4 (s)Ca2+(aq)SO42-(aq)
I (Initial)--0 M1.4 × 10-2 M
C (Change)--+ x1.4 × 10-2 M + x
E (Equilibrium)--x1.4 × 10-2
Sub the molar solubility at equilibrium, 'x' into the solubility product constant equation... This is the (molar) solubility...

The Common Ion Effect

The solubility product constant of barium nitrate Ba(NO3)2 at 25˚C is,

Calculate the molar solubility of barium nitrate in pure water. Solution
Hint Clear Info
× 10
Incorrect Attempts:
CHECK
M
Hint Unavailable
ICE table,
Ba(NO3)2 (s)Ba2+(aq)2NO3-(aq)
I (Initial)--0 M0 M
C (Change)--+ x+ 2x
E (Equilibrium)--x2x
Sub into Ksp to find molar solubility of barium nitrate...

Given the molar solubility of barium iodate, Ba(IO3)2 in pure 25˚C water is 1 × 10-3 M, calculate the solubility product constant (Ksp) of barium iodate. Solution
Ksp =
Hint Clear Info
× 10
Incorrect Attempts:
CHECK
Hint Unavailable
ICE-ice baby,
Ba(IO3)2 (s)Ba2+(aq)2IO3-(aq)
I (Initial)--0 M0 M
C (Change)--+ x+ 2x
E (Equilibrium)--x2x
Calculate,

Calculate the molar solubility of barium iodate in a saturated solution of barium nitrate. Solution
Hint Clear Info
× 10
Incorrect Attempts:
CHECK
M
Hint Unavailable
Starting with some initial concentration of barium, Ba2+(aq) this time because it is a saturated solution of barium nitrate... The amount of iodate still starts at zero because the barium iodate starts as all solid first...
Ba(IO3)2 (s)Ba2+(aq)2IO3-(aq)
I (Initial)--1 × 10-1 M0 M
C (Change)--1 × 10-1+ x+ 2x
E (Equilibrium)--1 × 10-1 + x2x
Can we neglect 'x'? Since > 100, then yes we can neglect 'x' where it is added or subtracted in the ICE table...
Ba(IO3)2 (s)Ba2+(aq)2IO3-(aq)
I (Initial)--1 × 10-1 M0 M
C (Change)--1 × 10-1 + x+ 2x
E (Equilibrium)--1 × 10-12x
Calculate,

Solubility and Precipitates

When a solution of calcium ions is dripped into a solution containing CaO and CaI2 compounds, the precipitate formed first will be the one with the solubility product (Ksp) exceeded first (lowest).

Volatile Products and Equilibrium

In an open beaker, adding more Ca2+ to the solution will significantly increase the amount of calcium carbonate precipitate. Solution
The volatile carbon dioxide gas bubbles out of the solution and will not be present for additional calcium ions to synthesize more calcium carbonate with. The formation of the volatile carbon dioxide gas creates a one-way reaction, as can be seen from the direction of the arrow in the equation. (There will be an insignificant increase in the amount of calcium carbonate precipitate, Le Chatelier's principle)

Flashcards: Chemical Systems & Equilibrium

At equilibrium are the forward and reverse reactions stopped?
No, the forward and reverse reactions are always occurring, even at equilibrium. At equilibrium the rate of the forward and reverse reactions are equal so there appears to be a balance.
State at least three ways to shift the equilibrium of this reaction to the left
Decrease pressure, increase volume, increase temperature, increase [H2O], decrease [H2] or [O2].
What does a low Keq value indicate?
[products] > [reactants]
Determine the correct Keq equation for:
What phases do not appear in the equilibrium constant (Keq) equation?
Pure solids and liquids do not appear.

(aqueous and gaseous do appear)
If the equilibrium constant for the forward reaction is Keq = 8, then what is the equilibrium constant for the reverse reaction?
What does a Keq much greater than and much less than 1 mean?
A Keq much greater than 1 means the concentration of the product is higher than the concentration of the reactant. A Keq much less than 1 means the concentration of the product is lower than the concentration of the reactant.

Acid-Base Equilibrium

Svante Arrhenius 1884

Arrhenius defined acids and bases as Solution
According to Arrhenius,
Acids are proton (H+) donors, and bases are hydroxide (OH-) donors

(Arrhenius' definitions become outdated when Brønsted and Lowry offered their definitions, and later Lewis...)

Johannes Brønsted and Thomas Lowry 1923

Brønsted and Lowry defined acids and bases as Solution
According to Brønsted and Lowry,
Acids are proton (H+) donors, and bases are proton (H+) acceptors

(Brønsted and Lowry's definition was more general than Arrhenius' and encompassed more circumstances)

Arrhenius, Brønsted-Lowry

Ammonia (NH3) violates which definition of a base? Solution
Ammonia does not contain hydroxide (OH-) ions.

For example in pure water, Ammonia, NH3 is a Brønsted-Lowry base because it is a proton acceptor, but is not a hydroxide donor according to Arrhenius' definition. (Arrhenius defined bases as hydroxide donors). As you can see the base, ammonia is a proton acceptor (Brønsted-Lowry base) but does not fall under the Arrhenius category of a base (hydroxide donor).

pH + pOH = 14

If the pOH of a solution is 8.4, then the pH is 1.6 Solution
pH + pOH = 14
pH = 14 - 8.4
pH = 5.6

Calculate pH, pOH, [H3O+], and [OH-] - without Kw

Calculate the pH of a solution with [H+(aq)] = 2.8 × 10-3 mol/L. Solution
Note that H+ = H3O+

Determine the pH of a solution with [OH-] = 1.0 × 10-6 mol/L Solution
pH =
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
Calculate pOH... Subtract from 14 using the equation... (Method II is to convert [OH-] to [H3O+] = 1.0 × 10-8 mol/L ... and then calculate the pH...)

Is it possible to have a negative pH? Explain. Solution
Hint Clear Info
Incorrect Attempts:
CHECK
Yes/no, plus explain
Yes it is possible for very strong acids when the concentration of proton or hydronium ions is greater than 1.0 for example, As you can see all it takes is for an acid with a high dissociation constant and a high molarity of the acidic protons. In this case the pOH would be 14.08

Polyprotic and Molar Equivalent (Normality)

A 1.0 mol/L solution of H2SO4 would have what effective equivalent of protons? Solution
[H+] =
Hint Clear Info
Incorrect Attempts:
CHECK
mol/L
Hint Unavailable
There are 2 protons in each molecule of H2SO4. Since this is a strong acid it dissociates almost completely.

This makes: 2(1.0 mol/L)
= 2.0 mol/L

pH with Bases

Calculate the pH of a solution prepared by completely dissolving 0.85 g of the strong base, Ca(OH)2 into 3.0 L of water. Solution
pH =
Hint Clear Info
Incorrect Attempts:
CHECK
Hint Unavailable
Be careful because calcium hydroxide is di-hydroxic - there are two hydroxides...

DON'T NEED TO USE ICE TABLES FOR THE STRONG ACIDS/BASES (ONLY USE ICE TABLES FOR THE WEAKER ONES THAT DONT FULLY DISSOCIATE)... Calculate concentration... without kb or ICE table because you assume the strong bases dissociates fully... Since there it is di-hydroxic... Calculate pOH Use the formula: pH + pOH = 14

Amphoteric

Which of the following compounds is not amphoteric? Solution
Amphoteric means that the molecule can act as either an acid or a base depending on what else is there with it in the surroundings. Of all the molecules: H2SO4 is the only molecule that is acidic and can't act as a base. Amphoteric compounds are not located on the far left or far right ends of the equations shown above.

Write the two separate reactions of water acting as an amphoteric acid and base. One reaction with the acid, H2SO4 and the other reaction with the base, NaOH. Solution
With H2SO4, H2O + H2SO4 ↔ H3O+ + HSO4- With NaOH, H2O + NaOH ↔ Na+OH- + H2O

Conjugates of Acids and Bases

Strong acids have strong conjugate bases. Solution
The stronger the acid, the weaker is its conjugate base.

The conjugate base of water in the following reaction is Solution
Water is acidic when it is with a compound that acts as a base. Water is amphoteric (acts as either acid or base) depending on the other reactant it is with. Here the water is weakly acidic and forms a strong conjugate base, OH-.

Based on your knowledge of conjugate acid-base strengths, which of the following is the strongest base? Solution
The following are all conjugate bases of strong acids, therefore they are weak bases: NaCl, NaNO3, Na2SO4, NaBr.

Weak acids have strong conjugate bases. The weak acetic acid (CH3COOH or C2H4O2) will have a strong conjugate base... C2H3O2- CH3COOH + H2O ↔ CH3COO- + H3O+ Therefore the acetate salt (NaCH3COO or NaC2H3O2) is the strongest base...

Mixing Strong/Weak Acids/Bases

Mixing equal moles of weak acid and strong base results in... Solution
Mixing equal moles is what matters most, and is needed for comparison. Mixing equal moles of weak acid and strong base always results in an alkaline/basic salt solution.

Mixing equal molarity (concentrations) of strong acids and weak bases, from two different containers, always results in an acidic solution. Solution
Not necessarily, while this is often true, there are some situations where it is not true. For instance, if the volume of the container of the base is far greater, then the total moles of base (OH-) is greater than the total moles of acid (H3O+), and the solution would be basic.

With acid and base mixtures, it is the total amount of moles of the acid and the base that is compared.

Fill in the blanks in the table with the different mixtures of strong or weak acids and bases... Solution
ReactionResult
Neutral
__________
__________
__________
__________
This year, you are expected to know the 6 common strong acids and 7 common strong bases, and apply this knowledge. You also need to know, Strong Acid + Strong Base ↔ Neutral Salt + Water
Weak Acid + Strong Base ↔ Basic/Alkaline Salt + Water
Strong Acid + Weak Base ↔ Acidic Salt + Water
ReactionResult
Neutral, both are strong
Basic/Alkaline, KOH is strong base, acetic acid is weak acid
Acidic, nitric acid is strong, and ammonia is weak base
Basic, H3PO4 is a weak acid and Ca(OH)2 is strong base
Neutral, both are strong

Calcium oxalate, Ca(C2O4)2 is the most common type of kidney stone, at around 80% of kidney stone occurrences. Classify this salt... Solution
Write the reaction with the simple Arrhenius base (-OH) and acid (-H) that makes the calcium oxalate salt. You should be able to determine this reaction on your own, Ca(OH)2 is one of the 7 most common strong bases and HC2O4 is a weak acid (because it is not on the list of the 6 common strong acids that you should know).

The salt of a strong base, Ca(OH)2 and weak acid, HC2O4 is an alkaline salt.

Determine the result of the solution when you mix the weak mono-protic acid and weak mono-hydroxic base, with the dissociation constants, k given below. [1] Solution
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The strength of an acid or base depends on its amount of dissociation - strong will dissociate almost completely into aqueous ions.

This weak acid will dissociate (dissolve) more than the weak base because the acid has the higher dissociation constant, k. Since each is mono-protic and mono-hydroxic (1 H and 1 OH), therefore the resulting solution will be slightly more acidic.

Precipitation of Strong and Weak Acids

A solution contains equal concentrations of the ions dissociated from a weak acid and a strong acid. Theoretically, if a common ion of the acid and base is added to the solution, the stronger acid will precipitate first. Solution
Strong acids dissolve to almost to completion compared to weak acids. The ions of strong acids are more stable when dissolved in solution and tend to stay dissolved, whereas weaker acids precipitate more.

The Ionization Constant of Water (Kw): Calculate pH, pOH, [H3O+], and [OH-]

Given [H3O+] = 10-4, the [OH-] equals Solution
Know the two formulas... See for yourself, in this table, as pH increases, pOH decreases by the same amount.
pH [H3O+] [OH-] pOH
1 10-1 10-13 13
2 10-2 10-12 12
3 10-3 10-11 11
4 10-4 10-10 10
5 10-5 10-9 9
6 10-6 10-8 8
7 10-7 10-7 7
8 10-8 10-6 6
9 10-9 10-5 5
10 10-10 10-4 4
11 10-11 10-3 3
12 10-12 10-2 2
13 10-13 10-1 1

The Ionization Constant of Water (Kw)

Derive the ionization constant of water, Kw using the weak acid, HF and your knowledge of Ka and Kb. Solution
For the acid, For the base, Since Kw = Ka × Kb... At SATP 25˚C, Kw = 1.0 × 10-14

Ka given Kb

Determine Ka given Kb = 5.0 × 10-3 at SATP. Solution
Ka =
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Hint Unavailable
Ka × Kb = Kw = 1.0 × 10-14

Describe what a high ka means. [1] Solution
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Since ka is the ratio of the concentration of products to the reactants, Then a high ka value means the reaction proceeds significantly to the right - to the products. This is a strong acid. Strength of an acid depends on the amount of dissociation into ions in solution.

Acid Ionization Ka

A 0.9M solution of hydrofluoric acid dissociates into 0.0237M [F-]. Calculate the Ka of the compound. Solution
Ka =
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Set up an ICE table to determine the ka...
HF --> H+ + F-

Base Ionization Kb

Ammonia is a common household cleaner that is highly soluble in water. A solution of ammonia forms ammonium and hydroxide in solution according to the following equation.

Determine an equation for the equilibrium ionization of the base, Kb. Solution

The value of Kb for ammonia is 1.8 × 10-5. If 0.25M of ammonia is dissolved, find how much ammonium is formed when ammonia ionizes. Solution
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M
Hint Unavailable

Calculate the pH of the solution. Solution
pH =
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Acid Ionization Ka with Triprotic Acids

Phosphoric acid, H3PO4 is a triprotic acid that dissociates fully into phosphate ions. The acid solubility constants are given below.

Ka 1 = 7.5 × 10-3
Ka 2 = 6.2 × 10-8
Ka 3 = 2.2 × 10-13

Write the three different dissociation reaction equations of phosphoric acid. Solution

If the initial concentration of H3PO4 is 0.01 M, calculate the concentration of H2PO4- ions at equilibrium. Solution
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M
Hint Unavailable
Make an ICE table.
You cannot neglect the change in 'x' because the ratio of initial reactant to the k value is greater than 100.
H3PO4 (aq)H+(aq)H2PO4-(aq)
I0.01 M0 mol/L0 mol/L
C- x+ x+ x
E0.01 M - xxx
Use the quadratic equation to solve...
Neglect the negative value, so the [H+] = [H2PO4-] = 0.00569 M.

Calculate the concentrations of hydrogen phosphate, HPO42- and phosphate, PO43- ions. Solution
Hint Clear Info
[HPO42-] = × 10
[PO43-] = × 10
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M
Hint Unavailable
Make the first ICE table for Ka 2.
! Watch out, make sure to use the values calculated previously... [H+] = [H2PO4-] = 0.00569 M.
H2PO4-(aq)H+(aq)HPO42-(aq)
I0.00569 M0.00569 mol/L0 mol/L
C- x+ x+ x
E0.00569 - x0.00569 - xx
Neglect 'x' because the ratio of the initial reactant to the Ka 2 value is greater than 100. The concentration, [H+2] = [HPO42-] = 6.2 × 10-8 M.
Now the total proton concentration, [H+] = [H+1] + [H+2] = 0.00569 M + 6.2 × 10-8 M = 0.00569 M.

Make the second ICE table using the values calculated...
HPO42-(aq)H+(aq)PO43-(aq)
I6.2 × 10-8 M0.00569 M0 mol/L
C- x+ x+ x
E6.2 × 10-8 - x0.00569 - xx
Neglect 'x' because the ratio of the initial reactant to the Ka 3 value is greater than 100. [PO43-] = 2.4 × 10-18 M.

Acid Base Titration

In a titration, a neutral pH is reached when in the same container: (More than one answer: check all that apply). Solution
The main neutral scenario is when: Moles of acid = moles of base But if the volume is the same, then it could also be: Concentration of acid = concentration of base

Equivalence Point

The equivalence point in a solution (in the same container) is reached when the number of moles (or concentration) of H3O+ = OH- Solution
n·H+(aq) = n·OH-(aq) If already in same container, then the volume is the same so the concentrations are directly proportional to the number of moles and concentration can be used/compared. But equivalence point is really always when the number of moles in solution are equal.

The equivalence point of an acid and a base will always occur at a pH of 7. Solution
The equivalence point usually is at a pH of 7.0 but not always...

While many equivalence points are at a pH of 7, particularly when a strong acid and a strong base are reacted, some combinations of weaker acids and bases will not be at 7.

Furthermore for polyprotic acids (H3PO4) and polyhydroxic bases, there are numerous equivalence points. The equivalence point is reached when one form has been reached fully... like once 0% H3PO4 and 100% H2PO4-...

Equivalence Point with pH ≠ 7

Answer at least one of the following...

Explain why titrating a weak base like Mg(OH)2 with a strong acid has an equivalence point pH < 7. Solution
The mole equivalent of acid = the mole equivalent of base at the equivalence point. However this does not necessarily mean that the solution is neutralized at a pH = 7. The weak base will have a strong conjugate acid, Mg2+ that will slightly react with surrounding water increasing the amount of H+ slightly as follows... Thus decreasing the pH of the solution slightly.

Explain why titrating a strong base like KOH with a weak acid has an equivalence point pH > 7. Solution
The mole equivalent of acid = the mole equivalent of base at the equivalence point. However this does not necessarily mean that the solution is neutralized at a pH = 7. The weak acid will have a strong conjugate base, A- that will slightly react with surrounding water increasing the amount of OH- slightly as follows... Thus increasing the pH of the solution slightly.

Titration of Mono-Protic Acid and Base

If 10mL of 0.50M NaOH is titrated to the equivalence point with 20mL of HCl, calculate the concentration of acid. Solution
Ca =
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mol/L
Hint Unavailable
nacid = nbase

Vacid∙Cacid = Vbase∙Cbase

The equivalence point is reached when neutral pH = 7.0 when the moles of acid equals the moles of base... This works since the base is mono-hydroxic, and the acid is mono-protic. (Note that it is not necessary to convert to L here... mL is fine...)

Titration of Di-Protic Acid and Base (Normality)

30mL of 1.0M Al(OH)3 is titrated with 2.0M H2SO4. Find the volume of acid required to reach equivalence point. Solution
V =
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mL
Hint Unavailable
Normality of 2.0M H2SO4 = 4.0M

nacid∙(numberacid ions) = nbase∙(numberbase ions)

Vacid∙Cacid∙(numberacid ions) = Vbase∙Cbase∙(numberbase ions)

Indicators

The indicator molecule itself is an acid or a base. Solution
An indicator is a molecule that changes its structure when it reacts as an acid or a base and usually leads to a color change.

Acid Base Terms: Endpoint

The endpoint in an acid-base reaction is the point at which Solution
The endpoint is reached when the indicator changes color. If the endpoint of a certain indicator is reached when pH = 7, then the endpoint is at the same point as the equivalence point. This is not always the case. You should choose the correct indicator for the pH you would like to reach/observe.

There are 100s of different indicators to choose from with many different pH end points between 0 - 14. Some indicators such as Thymol Blue have multiple end points (pH ≈ 3, & 9). The transition of an indicator occurs over a range of pH and is difficult to pinpoint.

Polyprotic Acid pKa

To calculate the pH of a polyprotic acid like H2SO4, the average of the Ka for the first proton dissociation and the Ka for the second proton dissociation, is used. Solution
The pH is calculated based on the first Ka value since the first dissociation is dissolved much more than the second dissociation.

Ka and pKa

Determine the Ka of a solution with pKa = 12 Solution
Ka =
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pKa = -log(Ka)
...
Ka = 1.0 × 10-12

Buffers

Which of the following is not always a characteristic of a good buffer? Solution
While a pH in the range of 6-8 is good, it is not only this range and there are many buffer than can exist in the lower or higher pH ranges - it depends more on what is being buffered. Although weakly acidic buffers are most common. (The rest of the answer choices are characteristics of buffers).

Describe the result of adding a highly concentrated, strong acid (H-X) to a weak, acidic buffer. The buffer exists in solution as: Solution
  • The weak acid buffer does not dissociate much (because it is weak) and exists mostly as reactant, and very little product.
  • The strong acid deprotonates into H+ and consumes the A- dissolved from the buffer to make more of the weak acid buffer HA, plus the dissolved ion X-.
  • The plentiful buffer acting as a base neutralizes the strong acid by making it into a much weaker acid.
  • The result is that the pH will not change (decrease) much. Buffers are very effective at buffering, or reducing the change in pH.

Describe the result of adding a highly concentrated, strong base (NaOH) to a weak, acidic buffer. The buffer exists in solution as: Solution
  • The strong base (OH-) will consume the hydronium, H3O+ ions in solution from the buffer... to form more water... neutralized.
  • Some salt ions from the base Na+ will remain in solution with the ion from the buffer A-.
  • The result is that the pH will not change (incrase) much. Buffers are very effective at buffering, or reducing the change in pH.

The Henderson-Hasselbach Equation with Buffers

A buffer is made by mixing 0.10M acid [HA] with 0.30M of its conjugate base [A-]. The pKa of this acid [HA] solution is 5.00. Assume that all the acid and base dissociates. If 0.05M of a strong acid is added to the solution, what is the new pH of the solution? Solution
pH =
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Hint Unavailable

Flashcards: Acids and Bases

Define a Brønsted-Lowry acid and base
An acid is a proton donor, and a base is a proton acceptor
Define a Lewis acid and base
An acid is an electron acceptor and a base is an electron donor
Is it possible to have a negative pH?
Yes
(At 25˚C)

pH + pOH =
14
(At 25˚C)

[OH-][H3O+] =
1 × 10-14
If the pOH of a solution at room temperature is 8.4, is it an acid or a base?
pH = 14 - 8.4 = 5.6

(this is an acid)
Is it possible to calculate the pH of a given mass of Ca(OH)2 in a given volume of water?
Yes
The conjugate base of a strong acid is weak or strong?
Weak
Strong acids dissociate/dissolve more or less than weak acids?
More
What is equivalence point?
The equivalence point in a solution is reached when the number of moles (or concentration) of H3O+ = OH-