Review and Final Examination

Purposes of Final Review

The questions are given for you to test your readiness.

The instructors will try to avoid these questions.

Review and Final Examination

There is no short cut to success. Time and effort are required to score high. Some problems used in past final examinations are posted. Instructors will avoid questions similar to these. However, you certainly will benefit from this review if you identify the theories and skills you think these questions test you.

Writing Exams

Answer these questions as if you are writing the examination. The practical experience will help you avoid minor mistakes. While writing out the answers, you also acquire the skills to put your answer in an organized way to earn higher marks than otherwise. Practice makes it perfect, and there is no replacement for practice. Treat the practice as an exam, and the exam will be a practice for you.

There are two sets of final exam questions on the course Internet. These are for you to practice writing exams, not the only thing to study.

Concentrate on answering one question at a time. If you are confused about the question and have no idea how to answer it, don't be panic. Skip it for the moment and come back to answer it if you have time. This way, you will earn all the marks for what you studied and know, instead of a complete break down and failing the exam.

Make sure to read the question carefully and answer the question directly. No marks will be awarded for a lot of beautiful writing.

Questions Requiring Written Answers

Chem 123/125 final examinations usually consist of two parts. Part A questions require written answers, whereas Part B questions are multiple choice.

Part A Questions are given in this link, and the Part B questions are given below.

Multiple Choice Example Questions

Some example questions are given in the order of the topics covered during this term. This way, you can relate to the topics you have reviewed. In the final examination, questions are in a random order following no set patterns. For Winter 1999, the exam consists of 30 multiple questions.

Intermolecular forces

Which one of the following lists the phase or phases that have the largest molar volume?
1. gas *
2. liquid
3. solid
4. gas and liquid
5. solid and liquid
Which substance has the highest molar heat of fusion?
1. carbon disulfide
2. argon
3. carbon dioxide
4. water
5. sodium chloride*
In a face-centred cubic (fcc) close packed structure, how many atoms are there in a fcc unit cell?
1. 1
2. 2
3. 4*
4. 8
5. 9
Silver (Ag) crystallizes in a fcc type structure with the cubic lattice edge of 407 pm. What is the average radius in pm, of a silver atom in the solid?
1. 2204
2. 156
3. 144*
4. 96
5. 72
Kinetics and Reaction Rate
The Haber process is the industrial method for the preparation of ammonia N₂ + 3 H₂ ® 2 NH₃
Starting with a closed vessel containing 1.250 M N₂ and 0.500 M H₂, it is found that H₂ concentration falls to 0.482 M after 3 seconds. Calculate the rate of NH₃ production.
Ans. 0.004 mol L^-1
For the reaction below, 2 NO + Cl₂ ® 2 NOCl
what is the relationship between
```
 d[NO]    d[Cl₂]       d[NOCl]
 -----,   ------, and  -------
  dt        dt           dt
```
Ans: they are equal if multiplied by the following coefficients
```
   - 1/2     - 1          1/2
```
The following data are obtained for a reaction at 300 K, A ® product
```
   time /s    0      20      40      60     80 
   [A]       5.0    4.44     3.92   3.46   3.06
```
What is the order of the reaction?
HINT. 1st; from plot log [A] vs time.
The following data are obtained for a reaction at 300 K, A ® product
```
   time /s    0      20      40      60     80 
   [A]       5.0    4.44     3.92   3.46   3.06
```
Calculate the reaction rate.
HINT. The order has to be determined first. 6.0e-3 /s; use the integrated rate law.
The activation energy is 182 kJ/mol for a gas phase reaction. At 973 K, the rate constant is 1.57e-5 /(M s). Calculate the rate at 1073 K.
Ans. 1.28e-4 /(M s)
The following reaction mechanism was proposed: 2 NO = N₂O₂ fast equilibrium
k1 for ®; k-1 for ¬
N₂O₂ + O₂ ® 2NO₂ very slow, k2 Derive the rate law:
Ans. rate = {k1 k2 /k-1} [NO]² [O₂]

Equilibria
A system of gases reach equilibrium according to the equation: Cl₂ + IBr = ClBr + ICl.
The equilibrium constant Kc = 1.0. If 2.0 moles each of Cl₂ and IBr and 4.0 moles each of ClBr and ICl are placed in a 1.0 liter container, what will be the concentration of ICl (in M or mol/L) when equilibrium is reached?
1. 1.0
2. 0.5
3. 2.0
4. 1.5
5. 3.0*
For the gases system: SO₂ + NO₂ = SO₃ + NO
at equilibrium, a 1.0 L sample contains 1.0 mol each of SO₂ and NO₂ and 4.0 mol each of SO₃ and NO. If 2.0 mol each of SO₃ and NO are added to the system at constant temperature, what will be the final concentration of NO₂ (in mol/liter) when the equilibrium is reestablished?
1. 16.0
2. 2.2
3. 1.4*
4. 0.4
5. 0.00
One mole of O₂ is added to a gaseous equilibrium system, S + O₂ = SO₂
in a 10.0 L container. How does the composition of the system change as it establishes a new equilibrium?
1. The amounts of all substances increase.
2. The amounts of S and O₂ increase; amount of SO₂ decreases.*
3. The amounts of S and O₂ decrease; amount of SO₂ increases.
4. The amount of S decreases; amounts of O₂ and SO₂ increase.
5. The amounts of all substances decrease.
Acids and Bases
Give the definition of Lewis acids. (or Bronsted-Lowry bases or Arrhenius acids, and be able to apply)
Ans. Lewis acids are electrophiles.
Give the conjugate base and conjugate acid for HPO₄^2-.
Ans. base, PO₄^3-; acid H₂PO₄^-
The pH is 2.43 for a 0.10 M solution of lactic acid, HC₃H₅O₃, at 298 K. K_w = 1e-14 at 298 K. What cannot be calculated from the above information?
1. Ka for HC₃H₅O₃
2. [H⁺]
3. percentage of ionization
4. K_b for HC₃H₅O₃*
5. [HC₃H₅O₃]
Which of the following will react with water to form an acidic solution?
1. NH₄⁺*
2. Cl^-
3. NH₃
4. SO₄^2-
5. ClO₄^-
For a particular acid and its conjugate base, what is the relationship between K_a, K_b, and K_w, or pK_a, pK_b and pK_w?
HINT pK_a + pK_b and pK_w from definition of K_a, K_b and K_w.
Derive this relationship.
Several problems related to titration expressed in the form of
- pH of weak acid or base
  Calculate the pH of a weak acid with concentration C_a.
- pH of a partially neutralized solution (same as buffer)
  
  Calculate the pH when 10 mL of 0.10 acetic acid is mixed with 2 mL of 0.20 M NaOH.
- pH at half-equivalence point (same as buffer problems)
  Calculate the pH at half equivalence point when 0.10 M acetic
  acid is titrated with 0.20 M NaOH.
- pH at equivalence point (same as hydration or hydrolysis problems)
  
  Calculate the pH of the equivalence point when 0.5 M acetic acid is titrated with 0.20 M NaOH.
  Calculate the pH of a 0.30 M sodium acetate solution.
- which indicator to use from a table of pKin values?
- plot of titration curve
The temperature of a 0.10 M H₂S solution is 298 K, and the atmospheric presure is 101.3 kPa. Which of the following cannot be calculated?
1. [H⁺] + [HS^-]
2. [H₂S] + [HS^-] + [S^2-]
3. density of H₂S solution*
4. [HS^-], [S^2-], and [OH^-]
5. pH + pOH
Sparingly Soluble Salts
For a saturated Mg(OH)₂ solution, the pH is 10.38. Calculate the K_sp for Mg(OH)₂.
ANS: 5.52e-11
What is the pH of a saturated Ca(OH)₂ solution? Ksp = 6.5e-6.
Ans: [OH] = 0.0235 M, pOH = 1.63; pH = 12.37.
What is the molar solubility of PbCl₂ in pure water?
Ans: 1.6e-2 M of PbCl₂.
Two solutions, 10.0 mL of 0.10 M Ca(NO₃)₂ and 10.0 mL of 0.10 M Na₃PO₃, are added and mixed. Choose the single correct or the single incorrect statement. You have to work out the truth or false for each and then decide.
1. A precipitate forms (Ca₃(PO₄)₂ pptd, K_sp on Data Sheet)correct
2. [NO₃^-] = 0.10 M correct
3. [H₂PO₄^-] + [HPO₄^2-] + [PO₄^3-] = 0.017 M correct
4. [Ca²⁺] = 0.05 M (No, 0.02 M)*incorrect
5. [Na⁺] = 0.15 M correct
Electrochemistry
Equal volumes of 1.0 M solutions of AuCl₃ and FeCl₂ are mixed. What are the reaction products (not including surplus reactants)?
1. Fe and Au
  
  Test your ability to tell relative
  reducing and oxidation power from the
  reduction potentials on Data Sheet.
2. Fe and Au³⁺
3. Fe²⁺ and Au
4. Fe³⁺ and Au³⁺
5. Fe³⁺ and Au*
Calculate the standard cell potential for Cd | Cd²⁺ || Ag⁺ | Ag.
Ans: From the data on the data sheet, you have E = 1.201 V
Calculate the K_sp for AgBr.
Ans: From the standard reduction potential of AgBr (0.0732 V) and Ag⁺ (0.799 V), use Nernst equation to calculate K_sp. = 5.5e-13.
Calculate the Cd²⁺ concentration x if the cell EMF is 0.240 V. Cd(s) | Cd²⁺ (x) || Ni²⁺ (1.0 M) | Ni(s) Ans: Find the standard reduction potential of Cd and Ni, and use the Nernst equation to calculate x = 3.2e-3 M
If 1.50 A of current flows through a solution containing AgNO₃ for 30 min, how much silver is deposited on the cathode?
Ans: 3.02 g.

Confidence Building Questions

Copper crystallizes in fcc structure. How many atoms are there per fcc unit cell?
Answer 4
Consider...
Draw the 3-dimensional structure.
The reduction potential for Zn²⁺ and Cu²⁺ are -0.761 V and 0.339 V respectively. Calculate the cell potential in V for the Daniel cell Zn | Zn²⁺ || Cu²⁺ | Cu.
Hint...For the reaction
Zn + Cu²⁺ ® Zn²⁺ + Cu.
E^o = 1.10 Discussion ...
What is the cell potential for
Cu | Cu²⁺ || Zn²⁺ | Zn ?

Review and Final Examination

Purposes of Final Review