Test 4 - Version 122 Exam 4 302 sutcliffe (51060) 1 This...

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Unformatted text preview: Version 122 Exam 4 302 sutcliffe (51060) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Zinc Silver 1 . 56 V V Voltmeter e e 1 M Zn 2+ (aq) 1 M Ag + (aq) Salt bridge to carry ions In this electrochemical cell, what is the cathode? 1. the solid silver electrode correct 2. the Ag + (aq) ions in the 1 M solution 3. the solid zinc electrode 4. the Zn 2+ (aq) ions in the 1 M solution Explanation: Zn(s) + 2 Ag + (aq) Zn 2+ (aq) + 2 Ag(s) Reduction occurs at the cathode. In this cell the reduction half reaction is Ag + (aq) + e Ag(s) . Ag + cations are attracted to the solid Ag electrode where they are reduced to Ag(s). 002 10.0 points Consider the reaction 2 Cu + (aq) Cu(s) + Cu 2+ (aq) . If the standard potentials of the Cu 2+ | Cu and Cu + | Cu couples are +0.34 and +0.52 V, respectively, calculate the value of E for the given reaction. 1. + 0.70 V 2.- 0.70 V 3. + 0.86 V 4. + 0.18 V correct 5.- 0.18 V Explanation: combine the 1/2 reactions in the following ways... 2 Cu+ + 2e- 2Cu +.52 V Cu Cu2+ 2e--.34 V That gives an overall potential of +.18 V 003 10.0 points Given the following standard reduction po- tentials Fe 3+ + e Fe 2+ +0.771 V Cu 2+ + 2 e Cu +0.337 V Sn 2+ + 2 e Sn- . 140 V Which of the following species would be the strongest oxidizing agent? 1. Cu 2+ 2. Fe 2+ 3. Sn 2+ 4. Sn 5. Fe 3+ correct 6. Cu 7. None of the species listed can act as an oxidizing agent. Explanation: 004 10.0 points Catalysts work by 1. increasing the kinetic energy of the reac- Version 122 Exam 4 302 sutcliffe (51060) 2 tant molecules. 2. increasing the diffusion rates (collision rate) of molecules in solution. 3. increasing the exothermicity of the reac- tion, which increases entropy in the surround- ings, making the reaction more favorable. 4. creating a new reaction path with a lower activation barrier. correct Explanation: Definition 005 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. less than 1.00 2. 4.00 3. 3.75 4. 0.253 5. 3.52 correct Explanation: 006 10.0 points The reaction 2 NO 2 (g) 2 NO(g) + O 2 (g) is postulated to occur via the mechanism NO 2 (g) + NO 2 (g) NO(g) + NO 3 (g) slow NO 3 (g) NO(g) + O 2 (g) fast. What is an intermediate in this reaction? 1. ON- NO 3 (g) 2. NO 3 (g) correct 3. NO(g) 4. NO 2 (g) 5. O 2 (g) Explanation: 007 10.0 points The principle of inhibiting the corrosion of iron by using a sacrificial anode is to allow 1. a metal that is more active than iron to function as a cathode....
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This note was uploaded on 02/06/2012 for the course CHEM 302 taught by Professor Mccord during the Fall '10 term at University of Texas at Austin.

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Test 4 - Version 122 Exam 4 302 sutcliffe (51060) 1 This...

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