Exam4_Solutions - Version 024 Exam 4 Sutcliffe (52410) 1...

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Unformatted text preview: Version 024 Exam 4 Sutcliffe (52410) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. SPECIAL NOTE: DUE TO THE LOG- ARITHMIC NATURE OF SOME OFTHE EQUATIONS YOU MAY FIND IF YOU DO NOT USE THE EXACT CONVER- SION TO KELVIN YOUR VALUE MAY BE SLIGHTLY DIFFERENT TO THE AN- SWER. IT SHOULD BE VERY CLOSE. 001 10.0 points Consider the voltaic cell Pt | H 2 (1 atm) | H + (? M) || Cl (1 M) | AgCl(s) | Ag 2 H + + 2 e H 2 E = 0.00 V AgCl + 1 e Ag + Cl E = 0.222 V If the measured cell potential for the cell is 0.430 volts, what is the pH of the solution? 1. 3.52 correct 2. 4.00 3. 0.253 4. less than 1.00 5. 3.75 Explanation: 002 10.0 points Given the standard electrode potentials Fe 3+ (aq) + 1 e Fe 2+ (aq) E = +0.771 V I 2 (s) + 2 e 2 I (aq) E = +0.535 V calculate K c at 25 C for the reaction 2 Fe 3+ (aq) + 2 I (aq) 2 Fe 2+ (aq) + I 2 (s) . 1. 1 . 61 10 12 2. 9 . 53 10 7 correct 3. 1 . 05 10 8 4. 1 . 02 10 4 5. 9 . 76 10 3 Explanation: 003 10.0 points NOTE: The question is just asking you about THESE Group 1B metals. Dont worry about other ones as you have no data for them. Consider the following standard reduction potentials: Cu 2+ + 2 e Cu E = 0 . 337 V Ag + + 1 e Ag E = 0 . 7994 V Au + + 1 e Au E = 1 . 68 V Which of the following statements about the ease of reduction of Group IB metal ions is true? 1. Cu 2+ is easier to reduce than Au + . 2. Ag + is easier to reduce than Au + . 3. Au is easier to oxidize than Ag. 4. Nothing can be predicted about the ease of reduction from the data given. 5. Ag + is easier to reduce than Cu 2+ . cor- rect Explanation: 004 10.0 points How many mL of a 0.001 M chloride solution must be added to a 100 mL solution of 7 . 2 10 5 M Ag + solution for AgCl to precipitate? K sp (AgCl) = 1 . 8 10 10 (Neglect dilution by the added Cl solution.) 1. Need to know the solution pH to solve this problem 2. 2.6 mL 3. 40.6 mL 4. 0.03 mL 5. 0.25 mL correct Explanation: 005 10.0 points Version 024 Exam 4 Sutcliffe (52410) 2 NOTE: C a and C b refer to the concentrations of acid and base used in the titration described below. The curve for the titration of nitrous acid (NH 2 ) with NaOH(aq) base is given below. 2 4 6 8 10 12 14 20 40 60 80 100 120 140 Volume of base (mL) pH Estimate the p K a of nitrous acid. C a = . 64, C b = 0 . 4608, and the volume of NH 2 is 100 mL. 1. 3 . 3 correct 2. None of these 3. 8 . 17 4. 72 5. 36 Explanation: K a = 4 . 5 10 4 C a = 0 . 64 C b = 0 . 4608 V NH 2 = 100 mL 2 4 6 8 10 12 14 20 40 60 80 100 120 140 Volume of base (mL) pH (72,8 . 17) (36,3 . 3) The equivalence point of this titration is when the curve is at an inflection point (nearly vertical); i.e. , at a volume of 72 mL ....
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Exam4_Solutions - Version 024 Exam 4 Sutcliffe (52410) 1...

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