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chm 2046 exam 2 key.pdf

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Department
Chemistry
Course Code
CHM 2046
Professor
Christou

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CHM 2046 / Prof. C. R. Martin EXAM 2 FORM A 3/6/2008 Please bubble in your name, UFID #, and form code on the answer sheet using a #2 pencil. 1. Determine the value of the equilibrium constant for the following reaction: AgBr +(s) O 2 3 (aq)↔ Ag(S O )2 3 2 (aq)+ Br -(aq) Use the data for the following two reactions: AgBr ↔ (s) +(aq) Br -(aq) K sp5.4×10 -13 + 2- 3- 13 Ag (aq) 2S O2 3 (aq) Ag(S O )2 3 2 (aq) K f 2.0×10 a. 2.7×10 -26 b. 2.0×10 13 c. 1.0×10 1 d. 5.4×10 -13 e. 3.7×10 25 2. The K of aenzoic acid is 1×10 . Which of the following would you choose as a pH = 4.0 buffer? a. A 1.0 M solution of benzoic acid b. A 1.0 L solution containing 1.0 mole of benzoic acid and 1.0 mole of sodium benzoate. c. A 1.0 L solution containing 1.0 mole of benzoic acid and 0.10 mole of sodium benzoate. d. A 1.0 L solution containing 0.10 mole of benzoic acid and 1.0 mole of sodium benzoate. e. A 1.0 L solution containing 0.10 mole of benzoic acid and 0.20 mole of sodium benzoate -36 3. What is the solubility of Pb (AsO 3 (s) [4 2 = 4.1×10 ] in a solute that is 0.02 M in Pb(NO ) ? 3 2 a. 5.6×10 -16 b. 3.6×10 -16 c. 8.0×10 -6 d. 7.2×10 -16 e. 4.1×10 -13 4. Which of the following equations best describes what takes place when the equivalence point is - reached in the titration of the weak base ClO (aq)with hydrobromic acid? a. H O3 +(aq) OH (aq)→ 2 H O 2 + - b. HClO (aq) H O2↔ H O 3 (aq)+ ClO (aq) c. ClO -(aq)+ H 2 ↔ HClO (aq)+ OH (aq) - - d. HClO (aq) OH (aq) ClO (aq)+ H 2 e. ClO -(aq) Br (aq)→ ClOBr 2-(aq) 5. Calculate the overall K for the complexation reaction: 2+ 2+ Zn (aq) + 4NH (aq) 3 Zn(NH ) 3 4 (aq), given the following stepwise formation constants: Zn + NH ↔ Zn(3H ) 32+ K f13.9×10 2 2+ 2+ 2 Zn(NH ) +3NH ↔ Zn(NH3) 3 2 K f22.1×10 Zn(NH ) 3 22++ NH ↔ 3n(NH ) 3 3+ K f31.0×10 2 2+ 2+ 1 Zn(NH ) 3 3 + NH ↔ 3n(NH ) 3 4 K f45.0×10 a. 5.0×10 1 b. 5.0×10 3 c. 4.1×10 9 d. 4.1×10 8 e. 3.0×10 11 6. Equal volumes of solutions (i) and (ii) are mixed together. Indicate which of the resulting mixtures will be a buffer. Solution (i) Solution (ii) a. 0.30 M HNO 2 0.22 M NaNO 2 b. 0.20 M HF 0.10 M KF c. 0.15 M NH 3 0.10 M NH Cl 4 d. 0.20 M C H 6OO5 0.25 M C H 6OO5a e. All of the above combinations will give a buffer solution 7. A hypobromous acid buffer is made with pH = 9.1. What is the ratio of moles of HOBr to moles of - - -9 OBr (HOBr /OBr)? K aor HOBr = 2.3×10 a. 2.89 b. 0.345 c. 0.690 d. 1.44 e. 9.10 8. When Al(NO ) is dissolved in water, it becomes a weak monoprotic acid with a K of 7.6×10 . -6
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