112, Chemistry Spring 2008, Section 1 (Hardy)
Name: __________________________________
Version M
Exam 3 (100 points) 16 Apr 2008
YOU MUST: (1) Put your name and student ID on the bubble sheet correctly. (2) Write the exam Version (A, B, etc.) on the upper left side of the bubble sheet above the word "NAME". This exam is Version "M" for Make-up. (3) Put all your answers on the bubble sheet. (4) When you are finished, turn the bubble sheet and the first page of the exam with your name on it. This exam has 27 required problems and 3 extra credit problems. Please keep your eyes on your own paper and your answers covered. Use the exam as scratch paper. We will not grade anything on the exam itself. Good luck!
Chem 112, Spring 07, Section 1
Exam 2
Name:_______________________________
Version M
1. Acids that ionize extensively in solution are referred to as a) dissociators. b) weak electrolytes. c) Arrhenius acids. d) Brnsted-Lowry acids. e) strong acids. Answer: e 2. Which of the following is never a Brnsted-Lowry acid in an aqueous solution? a) hydrogen chloride, HCl(g) b) dihydrogen sulfide, H2S(g) c) ammonium chloride, NH4Cl(s) d) hydrogen fluoride, HF(g) e) magnesium oxide, MgO(s) Answer: e 3. In the following reaction HF(aq) + HPO42-(aq) F-(aq) + H2PO4-(aq) a) HF is an acid and F- is its conjugate base. b) HF is an acid and F- is its conjugate acid. c) HPO42- is an acid and H2PO4- is its conjugate base. d) H2PO4- is an acid and F- is its conjugate base. e) HPO42- is an acid and HF is its conjugate acid. Answer: a 4. A solution is prepared by diluting 0.16 mol HNO3 with water to a volume of 1.5 L. What is the pH of this solution? a) -0.80 b) 0.80 c) 0.97 d) 1.83 e) 2.24 Answer: c 5. Which one of the following aqueous solutions will have a pH of 10.00 at 25 C? a) 1.0 101 M HCl b) 1.0 102 M HNO3 c) 1.0 10-4 M HBr d) 1.0 10-4 M NaOH e) 1.0 102 M KOH
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Chem 112, Spring 07, Section 1
Exam 2
Name:_______________________________
Version M
Answer: d 6. What is the pOH of 0.28 M HCl (aq) at 25 C? a) -0.55 b) 0.28 c) 0.55 d) 1.27 e) 13.45 Answer: e 7. Which of the following chemical equations corresponds to the base ionization constant, Kb, for nitrite ion (NO2-)? a) HNO2(aq) + H2O() NO2-(aq) + H3O+(aq) b) NO2-(aq) + H2O() HNO2(aq) + OH-(aq) c) HNO2(aq) + OH-(aq) NO2-(aq) + H2O() d) NO2-(aq) + OH-(aq) HNO32-(aq) e) NO2-(aq) + H3O+(aq) HNO2(aq) + H2O() Answer: b 8. Benzoic acid has a pKa value of 4.20. What is the value of Kb for sodium benzoate? a) 9.8 10-10 b) 1.6 10-10 c) 7.7 10-5 d) -4.2 e) 4.2 Answer: b 9. Assuming equal initial concentrations of the given species, which of the following weak acids has the strongest conjugate base in an aqueous solution? a) acetic acid b) formic acid c) hydrogen sulfite ion d) nitrous acid e) phosphoric acid Answer: c 10. Which salt produces a pH-neutral aqueous solution at 25 C? a) KBr b) NH4Cl c) NaNO2 d) KF Answer: a e) FeCl3
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Chem 112, Spring 07, Section 1
Exam 2
Name:_______________________________
Version M
11. In the following reaction mixing 1L of 1M HF and 1L of 1M NH3, what controls the pH of the resulting solution? HF(aq) + NH3(aq) NH4+(aq) + F-(aq) Ka (HF) = 7.2 10-4 Ka (NH4+) = 5.6 10-10 a) Ka (HF) b) Kb (F-) c) Ka (NH3) d) Ka (NH4+) e) both Ka (NH4+) and Ka (HF) Answer: d 12. What is the result of mixing equal molar quantities of a strong acid with a weak base? a) neutral solution b) an acidic solution c) a basic solution d) a salt solution with a pH dependent on the ratio of Ka and Kb e) a neutralization reaction with heat produced Answer: b 13. What is the concentration or HCO2- in a 0.001 M solution of formic acid? a) 4.2 x 10-4 b) 3.4 x 10-4 c) 7.0 x 10-4 d) 1.0 x 10-5 e) 3.6 x 10-6 Answer: b 14. Codine is a commonly prescribed pain killer that acts as a base. Calculate the pH of a 0.35
M aqueous solution of codeine (C18H21O3N, Kb = 8.9x 10-7). a) 3.2 b) 5.6 c) 8.4 d) 10.8 e) 12.5
Answer: d
15. Of the following list of molecules and ions, which can behave as Lewis bases: BH3, NH3, Cl-, Al3+? a) BH3 only b) NH3 and Clc) Al3+ and NH3 d) Cl- and BH3 e) Cl- and Al3+
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Chem 112, Spring 07, Section 1
Exam 2
Name:_______________________________
Version M
Answer: b 16. What is the effect of adding 10 mL of 0.1 M NaOH(aq) to 100 mL of 0.2 M NH4+(aq)? 1. The pH will decrease. 2. The concentration of NH3 will increase. 3. The concentration of NH4+ decrease. will a) 1 only b) 2 only c) 3 only d) 2 and 3 e) 1, 2, and 3 Answer: d 17. Which of the following combinations would be the best to buffer an aqueous solution at a pH of 5.0? a) H3PO4 and H2PO4b) HNO2 and NO2c) CH3CO2H and CH3COOd) H2PO4- and HPO42 e) NH4+ and NH3 Answer: c 18. Each of the following mixtures can produce an effect buffer solution EXCEPT a) HClO4 and NaClO4. b) HF and NaF. c) NaHCO3 and Na2CO3. d) Na2HPO4 and Na3PO4. e) NH4Cl and NH3. Answer: a 19. All of the following statements concerning buffers are true EXCEPT a) buffers are resistant pH changes upon addition of small quantities of strong acids or bases. b) buffers are used as colored indicators in acid-base titrations. c) the pH of a buffer is close to the pKa of the weak acid from which it is made. d) buffers contain appreciable quantities of a weak acid and its conjugate base. e) buffers are resistant to changes in pH when diluted with water. Answer: b
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Chem 112, Spring 07, Section 1
Exam 2
Name:_______________________________
Version M
20. An aqueous solution contains 0.224 M Na2SO3 and 0.469 M HSO3-. What is the pH of
this solution? a. b. c. d. e. Answer c
6.01 6.47 6.89 7.11 7.53
21. An aqueous solution contains 0.29 M ammonia. One liter of this solution could be converted into a buffer by the addition of which of the solutions below? (Assume that the volume remains constant as each substance is added.) a. b. c. d. e. Answer c
22. How many grams of solid potassium cyanide (KCN) should be added to 2.00 L of a
0.15 mol Ca(OH)2 0.15 mol NH4I 0.15 mol HClO4 0.29 mol CaI2 0.30 mol HClO4
0.226 M hydrocyanic acid (HCN) solution to prepare a buffer with a pH of 10.000 ? a. b. c. d. e. Answer a
23. How many moles of potassium hydroxide would have to be added to 225 mL of a
118 g 59 g 11.8 g 5.9 g 0.118 g
0.429 M acetic acid solution, in order to prepare a buffer with a pH of 4.680. a. 450 b. 45 c. 4.5 d. 0.45
e. 0.045
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Chem 112, Spring 07, Section 1
Exam 2
Name:_______________________________
Version M
Answer e 24. What kind of titration is shown in the graph at the right? (The volume of added titrant is shown on the x axis.) a. Titration of a weak monprotic acid with a strong base. b. Titration of a weak acid with a weak base. c. Titration of a strong acid with a strong base. d. Titration of a weak base with a strong acid. e. Titration of a weak polyprotic acid with a strong base. Answer: e 25. Which one of the following conditions is always met at the equivalence point of the titration of a monoprotic weak base with a strong acid? a) The pH of the solution is equal to 7.00. b) The volume of acid added ...