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CH302 Homework 9-solutions

CH302 Homework 9-solutions - Bodet(ngb299 Homework 9...

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Bodet (ngb299) – Homework 9 – sutcli ff e – (51630) 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. A NOTE ON CELL DIAGRAMS: When the diagram is more complex than A | B || C | D then you should just assume everything on the LEFT of the || is for the ANODIC re- action, and everything on the RIGHT of the || is the CATHODIC reaction. A | indicates a phase boundary. A comma often sepa- rates two species that are both in the same phase. Find a reduction half reaction in ta- ble 11.1 (Appendix table 5.5 is the same) that includes all of the items in your anodic reac- tion, then find one that includes everything in the cathodic reaction. Use these to write down your two half reactions and calculate your standard cell potential. If Pt is listed on the far left or right it is just an inert electrode, ignore it. Remember you have written a lot of K’s in the last two chapters. If you can find two redox couples that will combine to form the reaction your K is for, then you can calculate K! 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 di ff erent electrodes. cor- rect 3. oxidation takes place at the cathode. 4. electrolytes are added to carry electrons between electrodes. 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 copper electrode 2. The solid zinc electrode correct 3. The Zn 2+ (aq) ions in the 1 M solution 4. The Cu 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. - 0.22 V 3. + 0.22 V correct
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Bodet (ngb299) – Homework 9 – sutcli ff e – (51630) 2 4. - 0.12 V 5. + 0.46 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?
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CH302 Homework 9-solutions - Bodet(ngb299 Homework 9...

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