Homework #12-solutions

Homework #12-solutions - clow(twc432 Homework#12...

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clow (twc432) – Homework #12 – holcombe – (51160) 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points Which type of battery is best for use in heart (cardiac) pacemakers? 1. alkaline 2. mercury 3. nickel-cadmium 4. lithium-iodine correct Explanation: Pacemaker batteries are placed inside the body cavity, so the battery must be small, last a long time and be made of non-toxic materials. Lithium-iodine batteries last up to 10 years. 002 10.0points In a lead-acid (storage) battery, the cathode is the 1. casing enclosing the entire battery. 2. positive plates, lead/PbO 2 . correct 3. negative plates, lead/spongy lead. 4. H 2 SO 4 electrolyte. Explanation: Reduction occurs at the cathode; the Pb in PbO 2 is reduced to Pb in PbSO 4 . 003 10.0points What current would be required to produce 19 . 7 g of Au(s) from Au 3+ (aq) in 4 hours? 1. 2 A correct 2. 0.67 A 3. 120 A 4. 395 A 5. 28945 A 6. 20 A Explanation: This is a 3-electron process. (19 . 7 g Au(s)) parenleftbigg 1 mol 197 g parenrightbigg = 0 . 1 mol Au(s) 4 hr = 14400 s It N e F = n p I = n p N e F t = 0 . 1(3)(96485) 14400 = 2 . 01 A 004 10.0points How long will it take to deposit 0.00235 moles of gold by the electrolysis of KAuCl 4 (aq) us- ing a current of 0.214 amperes? 1. 26.5 min 2. 70.7 min 3. 53.0 min correct 4. 17.7 min 5. 106 min Explanation: 005 10.0points Two Faradays of electricity are passed through each of the following solutions: AgNO 3 (aq); CuSO 4 (aq); Bi(NO
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