Homework 9-solutions

Homework 9-solutions - phan (dtp377) – Homework 9 –...

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Unformatted text preview: phan (dtp377) – Homework 9 – sutcliffe – (51045) 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points In a galvanic cell, 1. electrical energy is used to reverse spon- taneous chemical reactions. 2. oxidation and reduction take place at the same time but at different electrodes. cor- rect 3. electrolytes are added to carry electrons between electrodes. 4. oxidation takes place at the cathode. Explanation: The reaction in a galvanic cell is sponta- neous and does not need to be driven by a battery. Both reduction and oxidation occur. 002 10.0 points Zinc Copper 1 . 10 V V Voltmeter e − e − 1 M Zn 2+ (aq) 1 M Cu 2+ (aq) Salt bridge to carry ions In this electrochemical cell, what is the an- ode? 1. The solid zinc electrode correct 2. The solid copper electrode 3. The Cu 2+ (aq) ions in the 1 M solution 4. The Zn 2+ (aq) ions in the 1 M solution Explanation: Zn(s) + Cu 2+ (aq) → Zn 2+ (aq) + Cu(s) Oxidation occurs at the anode. In this cell the oxidation half reaction is Zn(s) → Zn 2+ (aq) + 2 e − Zn atoms in the solid Zn electrode are oxidized to Zn 2+ ions; the electrode slowly erodes. 003 10.0 points The standard potential of the cell Ag(s) | AgCl(s) | Cl − (aq) || Cu 2+ (aq) | Cu(s) is +0.12 V at 25 ◦ C. If the standard potential of the Cu 2+ | Cu couple is +0.34 V, calculate the standard potential of the AgCl | Ag,Cl − couple. 1. + 0.46 V 2.- 0.12 V 3. + 0.22 V correct 4.- 0.46 V 5.- 0.22 V Explanation: 004 10.0 points If the standard potentials for the cou- ples Fe 3+ | Fe 2+ , MnO 2 − 4 , H + | Mn 2+ , H 2 O, Zn 2+ | Zn, V 3+ | V 2+ , and Br 2 | Br − are +0.77, +1.51,- 0.76,- 0.26, and +1.09 V, respec- tively, which is the strongest oxidizing agent? 1. MnO 2 − 4 correct 2. Fe 3+ 3. Mn 2+ 4. Br 2 phan (dtp377) – Homework 9 – sutcliffe – (51045) 2 5. Zn 2+ Explanation: 005 10.0 points Hint: Once you have decided which way elec- trons flow in the external circuit, what sub- stance is AT each of the electrodes? Consider the voltaic cell: Pt Sn 4+ (0.0010 M), Sn 2+ (0.10 M) Ag + (0.010 M) Ag Sn 4+ + 2 e − → Sn 2+ E = +0 . 15 V Ag + + 1 e − → Ag(s) E = +0 . 80 V The electrons flow in the external circuit from 1. Sn 2+ to Ag + . 2. Pt to Ag. correct 3. Sn to Ag. 4. Ag to Sn 4+ . 5. Ag to Pt. Explanation: 006 10.0 points Hint for this question: each statement implies that you should write out the two appropriate half reactions and determine if the process is spontaneous....
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This note was uploaded on 03/26/2012 for the course CHEM 302 taught by Professor Mccord during the Fall '10 term at University of Texas.

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Homework 9-solutions - phan (dtp377) – Homework 9 –...

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