Chemistry 112 Name _______________________

Exam I Form A Section _______________________

February 12, 2008 Student No. _______________________

IMPORTANT: On the scantron (answer sheet), you MUST clearly fill your name, your student number, section number, and test form (white cover = test form A; yellow cover = test form B). Use a #2 pencil.

There are 25 questions on this exam. Check that you have done all of the problems and filled in the first 25 bubbles on the scantron. The maximum score on this exam is 25 points. Your score will be reported in percent (max 100%).

Exam policy

• Calculators with text-programmable memory are not allowed. • Relevant data and formulas, including the periodic table, are attached at the end of

this exam. • Your grade will be based only on what is on the scantron form. • The answer key will be posted on the web after the exam (on the Exam Schedule

page).

Hints

• As you read the question, underline or circle key words to highlight them for yourself. Avoid errors from "mis-reading" the question.

• Pay attention to units and magnitudes (decimal places) of numbers obtained from calculations.

• There is no penalty for guessing.

CHEMISTRY 112 EXAM Feb. 12, 2008

FORM A ------------------------------------------------------------------------------------------------------------ 1. A burning splint will burn more vigorously in pure oxygen than in air because

A. oxygen is a reactant in combustion and the concentration of oxygen is higher in pure oxygen than it is in air.

B. oxygen is a catalyst for combustion. C. oxygen is a product of combustion. D. nitrogen is a product of combustion and the system reaches equilibrium at a

lower temperature. E. nitrogen is a reactant in combustion and its low concentration in pure oxygen

catalyzes the combustion. ------------------------------------------------------------------------------------------------------------ 2. A key reaction in the upper atmosphere involving ozone (O3) is:

O3(g) + O(g) 2 O2(g)

For this reaction, Ea = 19.0 kJ/mol and the overall energy change for the reaction (ΔE) is –392.0 kJ/mol. What is the activation energy for the reverse reaction? [2 O2(g) O3(g) + O(g)]

A. 392.0 kJ/mol B. 19.0 kJ/mol C. 373.0 kJ/mol D. – 373.0 kJ/mol E. 411.0 kJ/mol

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------------------------------------------------------------------------------------------------------------ 3. The rate of disappearance of HBr in the gas phase reaction

2 HBr (g) → H2 (g) + Br2 (g)

is 0.190 M s−1 at 150 °C. What is the rate of appearance of Br2(g)?

A. 2.63 M s-1 B. 0.095 M s-1 C. 0.0361 M s-1 D. 0.380 M s-1 E. 0.436 M s-1

------------------------------------------------------------------------------------------------------------ 4. A 0.1 M solution of a chemical substance has a pH of 4. The chemical substance is

A. a strong acid. B. a strong base. C. a weak acid. D. a weak base. E. not an acid or a base.

------------------------------------------------------------------------------------------------------------ 5. What are the conjugate acid and conjugate base of the following ion, H2PO4

−:

A. conj. acid: H3O+ and conj base: HPO42−

B. conj. acid: H3O+ and conj base: PO43−

C. conj. acid: H3PO4 and conj base: OH− D. conj. acid: HPO4

2− and conj base: PO42−

E. conj. acid: H3PO4 and conj base: HPO42−

------------------------------------------------------------------------------------------------------------ 6. Which of the following is the most acidic solution?

A. [OH−] = 0.5 M B. [H+] = 0.3 M C. pOH = 5.9 D. pH = 1.2 E. [H+] = 1 x 10−4 M

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------------------------------------------------------------------------------------------------------------ 7. Based on the following reaction profile, which of the following is correct?

1. The first step of the reaction is the rate-limiting step

2. There are two intermediates 3. There are two transition states

A. 1 and 2 only B. 1 and 3 only C. 2 only D. 3 only E. 2 and 3 only

------------------------------------------------------------------------------------------------------------ 8. Consider the following equilibria and their respective equilibrium constants:

C(s) + CO2 (g) 2 CO(g) 2.7 × 10−7

CO(g) + ½ O2 (g) CO2 (g) 5.2 × 1026

What is the equilibrium constant Keq for the reaction shown below?

C(s) + ½ O2 (g) CO(g) Keq = ???

A. 1.4 × 1020 B. 1.18× 1010 C. 1.9× 1033 D. 2.7× 1023 E. 7.14× 10−20

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------------------------------------------------------------------------------------------------------------ 9. The data in the table below were obtained for the reaction:

A + B → P

Experiment Number [A] (M) [B] (M)

Initial Rate (M/s)

1 0.273 0.763 2.83 2 0.273 1.526 2.83 3 0.819 0.763 25.47

What is the magnitude of the rate constant?

A. 38.0 B. 0.278 C. 13.2 D. 42.0 E. 2.21

------------------------------------------------------------------------------------------------------------ 10. At elevated temperatures, nitrogen dioxide decomposes to nitrogen oxide and

oxygen:

2 2

1NO (g) NO (g) + O (g)

2!

The reaction is second order in NO2 with a rate constant of 0.543M−1 s −1at 300°C. If the initial [NO2] is 0.260 M how long will it take for the concentration to drop to 0.100 M?

A. 3.34 s B. 8.8 × 10−2 s C. −0.611s D. 0.299 s E. 11.3 s ------------------------------------------------------------------------------------------------------------

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------------------------------------------------------------------------------------------------------------ 11. It requires 50 seconds for a first-order reaction to go 75% of the way to completion.

What is the half-life of the reaction? A. 25 seconds B. 120 seconds C. 20 seconds D. 100 seconds E. None of the above is within 5% of the correct answer. ------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------ For the next two questions, consider the following mechanism which involves the oxidation of iodide ion by hydrogen peroxide in acid solution: Step 1 (slow) H2O2(aq) + I–(aq) H2O(l) + OI–(aq) Step 2 (fast) H+(aq) + OI–(aq) HOI(aq) Step 3 (fast) HOI(aq) + H+(aq) + I–(aq) I2(aq) + H2O(l)

------------------------------------------------------------------------------- 12. Which of the following statements are true?

A. OI– and HOI are catalysts B. OI– and HOI are intermediates C. OI– is a catalyst and HOI is an intermediate D. HOI is a catalyst and OI– is an intermediate E. There are no catalysts or intermediates in this mechanism.

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13. For the mechanism above to be consistent with the kinetic data, what must be the experimental rate equation?

A. Rate = k [H2O2] [H+]2 [I–]2 B. Rate = k [I2] [H2O]2 C. Rate = k [H2O2] [I–] D. Rate = k [H+] [OI–] E. Rate = k [HOI] [H+] [I–]

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------------------------------------------------------------------------------------------------------------ 14. Which of the following does a catalyst do to a chemical reaction? 1. Lower the overall activation energy 2. Provide a different reaction mechanism 3. Change the overall energy of the reaction (ΔE) 4. Increase the rate at which equilibrium is achieved 5. Change the equilibrium constant

A. 1, 2, and 4 only B. 1, 2, and 3 only C. 1 and 2 only D. 1, 4, and 5 only E. All of these (1, 2, 3, 4, and 5)

------------------------------------------------------------------------------------------------------------ 15. The rate constant for the reaction between CO2 and OH– in aqueous solution to give

the HCO3– ion is 1.50 × 1010 L mol-1 s-1 at 25.0 ºC. Calculate the rate constant at

37.0ºC (body temperature), given that the activation energy for the reaction is 38.0 kJ/mol.

A. 4.36 × 109

B. 8.27 × 109 C. 1.50 × 1010 D. 2.72 × 1010 E. 3.66 × 1089

------------------------------------------------------------------------------------------------------------ 16. The removal of sulfur from coal and natural gas can be done by the reaction of H2S

with oxygen after the combustion of the fuel.

2H2S(g) + O2(g) 2S(s) + 2H2O(g) If the removal of H2S is a desirable result, which one of the following will NOT promote this process?

A. increasing O2 pressure B. condensing H2O(g) to H2O(l) C. removing some of the S(s) D. increasing the total pressure by compressing the system E. decreasing the pressure of H2O(g)

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------------------------------------------------------------------------------------------------------------ 17. What is the expression for the equilibrium constant for the following reaction?

NOCl(g) NO(g) + 1/2 Cl2(g)

A.

!

Keq =NOCl[ ]

Cl2[ ] NO[ ]

B.

!

Keq =NOCl[ ]

NO[ ] Cl2[ ]

C.

!

Keq =12Cl2[ ] NO[ ]

NOCl[ ]

D.

!

Keq =NO[ ] Cl2[ ]NOCl[ ]

E.

!

Keq =NOCl[ ]

12Cl2[ ] NO[ ]

------------------------------------------------------------------------------------------------------------ 18. For the hypothetical reaction

A(g) + 2 B(g) C(g)

at room temperature, Kp = 1 × 10−2. If 1.0 atm of A(g), 1.0 atm of B(g), and 1.0 atm of C(g) are introduced into a 1 L flask and allowed to react

A. more C(g) will form B. the reaction will achieve equilibrium within 1 second C. the reaction will take two days to reach equilibrium D. the equilibrium concentration of A(g) will be 1 x 10-2 atm E. the concentration of C(g) will decrease

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------------------------------------------------------------------------------------------------------------ 19. The pKw of water at 200°C is 11.2. What is the pH of pure water at 200°C?

A. 11.2 B. 7.0 C. 5.6 D. 4.2 E. 3.3

------------------------------------------------------------------------------------------------------------ 20. 42.3 mL of 0.472M HCl is mixed with 78.1 mL of 0.156M HNO3. What is the pH

of the final solution?

A. 0.323 B. 0.573 C. 0.807 D. 1.32 E. 1.86

------------------------------------------------------------------------------------------------------------ 21. HZ is a weak acid. An aqueous solution of HZ is prepared by dissolving 0.020

mol of HZ in sufficient water to yield 1.00 L of solution. The pH of the solution was 4.34 at 25oC. What is Ka of HZ?

A. 4.6 × 10−5 B. 6.9 × 10−9 C. 2.8 × 10−12 D. 1.4 × 10−10 E. 1.0 × 10−7

------------------------------------------------------------------------------------------------------------ 22. What are the spectator ions in the solution after the complete neutralization reaction

occurs when mixing the strong base NaOH(aq) and the weak acid HClO2(aq)?

A. ClO2−

B. OH− and Na+ C. H+ and OH− D. Na+ E. Na+ and ClO2

− ------------------------------------------------------------------------------------------------------------

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------------------------------------------------------------------------------------------------------------ 23. A student studies a first order reaction under several different conditions and gets the

results shown in the plot below. Which of the following conclusions about these experiments are correct?

1. Reactions 1 and 2 were done at the same temperature but with different starting concentrations.

2. Reactions 2 and 3 were done at the same temperature but with different starting concentrations.

3. Reaction 2 was done at a lower temperature than reaction 3.

A. only 1 is correct B. only 2 is correct C. only 3 is correct D. 1 and 3 are correct. E. 2 and 3 are correct.

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------------------------------------------------------------------------------------------------------------ 24. B is a weak base. Which reaction corresponds to the equilibrium constant Kb for

B(aq)?

A. B(aq) + H3O+(aq) HB+(aq) + H2O(l)

B. HB+(aq) + OH−(aq) B(aq) + H2O(l)

C. HB+(aq) + H2O(l) H3O+(aq) + B(aq)

D. HB+(aq) + OH−(aq) B(aq) + H2O(l)

E. B(aq) + H2O(l) HB+(aq) + OH−(aq)

------------------------------------------------------------------------------------------------------------ 25. The concentration of a hydroxylamine solution is 0.050M. What is the concentration

of hydroxide ion in the solution? The Kb of hydroxylamine (HONH2) is 1.1×10−8.

A. 0.050M B. 1.8 ×10−5M C. 4.3×10−10M D. 1.0×10−4M E. 2.3×10−5M

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END OF EXAM