Exam4_Solutions

Exam4_Solutions - Version 024 Exam 4 Sutclie(52410 This...

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Version 024 – Exam 4 – Sutclife – (52410) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices be±ore answering. SPECIAL NOTE: DUE TO THE LOG- ARITHMIC NATURE O² SOME O²THE EQUATIONS YOU MAY ²IND I² YOU DO NOT USE THE EXACT CONVER- SION TO KELVIN YOUR VALUE MAY BE SLIGHTLY DI²²ERENT 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 = 0.00 V AgCl + 1 e Ag + Cl E 0 = 0.222 V I± the measured cell potential ±or the cell is 0.430 volts, what is the pH o± 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 ²e 3+ (aq) + 1 e 2+ (aq) E 0 = +0.771 V I 2 (s) + 2 e 2 I (aq) E 0 = +0.535 V calculate K c at 25 C ±or the reaction 2 ²e 3+ (aq) + 2 I (aq) 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 ±or them. Consider the ±ollowing standard reduction potentials: Cu 2+ + 2 e Cu E 0 = 0 . 337 V Ag + + 1 e Ag E 0 = 0 . 7994 V Au + + 1 e Au E 0 = 1 . 68 V Which o± the ±ollowing statements about the ease o± reduction o± 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 o± reduction ±rom the data given. 5. Ag + is easier to reduce than Cu 2+ . cor- rect Explanation: 004 10.0 points How many mL o± a 0.001 M chloride solution must be added to a 100 mL solution o± 7 . 2 × 10 5 M Ag + solution ±or 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
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Version 024 – Exam 4 – Sutclife – (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. 0 2 4 6 8 10 12 14 0 20 40 60 80 100 120 140 Volume oF base (mL) pH Estimate the p K a oF nitrous acid. C a = 0 . 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 0 2 4 6 8 10 12 14 0 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 in±ection point (nearly vertical); i.e. , at a volume oF 72 mL . The pH at the equivalence point oF this titration is 8 . 17 pH . The p K a can be Found at one-halF the vol- ume oF the equivalence point; i.e. , at 36 mL. The p K a is 3 . 3 pH From looking at the graph.
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Exam4_Solutions - Version 024 Exam 4 Sutclie(52410 This...

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