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Unformatted text preview: sy3475 Homework 5 Sutcliffe (53980) 1 This print-out should have 17 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points An electrochemical cell is a device that con- verts chemical energy into 1. electrical energy. correct 2. light energy. 3. chemical energy. 4. nuclear energy. Explanation: 002 10.0 points To correctly balance the half reaction Pu 4+ Pu 3+ , what would you need to add? 1. one electron to the right 2. three protons to the left and four protons to the right 3. four protons to the left and three protons to the right 4. four electrons to the left and three elec- trons to the right 5. three electrons to the left and four elec- trons to the right 6. one proton to the left 7. one electron to the left correct 8. one proton to the right Explanation: The balanced half reaction is Pu 4+ + e- Pu 3+ , 003 10.0 points Zinc (Anode) Silver (Cathode) 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 ox- idation half reaction? 1. Zn 2+ (aq) + 2 e- Zn(s) 2. Zn(s) Zn 2+ (aq) + 2 e- correct 3. Ag + (g) + e- Ag(s) 4. Ag(s) Ag + (g) + e- Explanation: Zn(s) + 2 Ag + (aq) Zn 2+ (aq) + 2 Ag(s) Oxidation occurs at the anode. In this cell the oxidation half reaction is Zn(s) Zn 2+ (aq) + 2 e- . 004 10.0 points What condition must be met for a battery to be rechargeable? 1. Either its anode or its cathode must gen- erate a gas as a result of the electrochemical reaction. 2. The battery must be open to the outside so that it can vent any internal pressure that builds up from gases within it. 3. It must generate electricity via an acid- base reaction rather than via an oxidation reduction reaction. sy3475 Homework 5 Sutcliffe (53980) 2 4. The electrochemical reaction of the bat- tery must be reversible. correct Explanation: Definition 005 10.0 points Why can the lead-acid batteries used in cars generate electricity for several years before running down ( i.e. , the battery is dead)? 1. The mechanical motion of the engine drives an alternator that generates electric- ity to recharge the battery. correct 2. The electrons they generate and not the chemical components provide most all of the electricity. 3. A lead-acid battery is so large that it holds large quantities of the chemicals whose electrochemical interaction creates the elec- tricity....
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This note was uploaded on 03/19/2008 for the course CH 305 taught by Professor Sutcliffe during the Spring '08 term at University of Texas at Austin.
- Spring '08