Exam%202%20Key%20SS2%20_02

Exam%202%20Key%20SS2%20_02 - Exam II Key, Chem 2B Summer...

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Exam II Key, Chem 2B Summer Session 2, 2002 1 Part I: Mult. Choice - No Partial Credit 1. (5 pts) Which of the following weak acids has the strongest conjugate base? A. HCN (K a = 4.8 x 10 -10 ) B. HSO 4 - (K a = 1.2 x 10 -2 ) C. HS - (K a = 7.1 x 10 -15 ) D. H 2 CO 3 (K a = 4.3 x 10 -7 ) E. None of the above. 2. (5 pts) For a system at equilibrium, reactants dominate if : A. K is small (< 10 -3 ) B. Q > K C. Q < K D. K is large (> 10 3 ) E. both A. and C. 3.(5 pts) The equilibrium constant for the reaction of KOH(aq) with HI(aq) is A. 1.0 x 10 28 B. 1.0 x 10 7 C. unknown D. 1.0 x 10 14 Net ionic eqn: H + + OH - H 2 O K = 1 / K w E. 1.0 x 10 -14 4. (5 pts) Which of the following salts gives an acidic aqueous solution? A. AlCl 3 acidic B. NaClO 4 neutral C. MgO basic D. Li NO 3 neutral E. CaCO 3 basic 5.(10 pts) At body temperature (37 ˚C), the osmotic pressure of blood (a 0.15 M NaCl solution) is 7.6 atm. Donated blood is refrigerated at 5.0 ˚C. Estimate the osmotic pressure of this solution at 5.0˚C: A. 9.1 atm B. 3.4 atm C. 13.6 atm D. 0.91 atm E. 6.8 atm Π = i MRT = 2 * 0.15M * 8.2x10 -2 L atm K -1 mol -1 * (37 + 273)K
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Exam II Key, Chem 2B Summer Session 2, 2002 2 6.(10 pts) Consider the following reaction NH 4 HS(s) NH 3 (g) + H 2 S(g) The value of K p for the reaction is 0.18 at 350 K. Calculate the equilibrium partial pressure of NH 3 (g) starting from pure NH 4 HS(s) A. 0.18 atm B. 0.055 atm C. 0.43 atm D. 0.032 atm E. Not enough info to calculate Soln: eqn NH 4 HS(s) NH 3 (g) + H 2 S(g) Init 0 0 ch -x +x +x fin x x K p = P NH3 * P H2S = x 2 = 0.18 x = 0.43 7.(15 pts) Consider the following reaction: 2NOCl(g) 2NO(g) + Cl 2 (g) If, initially [NOCl] = 3.80 M, all others are zero, and at equilibrium, [NO] = 1.22 M, calculate the value of K c . A. 2.58
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Exam%202%20Key%20SS2%20_02 - Exam II Key, Chem 2B Summer...

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