Homework 9-solutions - le(chl528 Homework 9 Sutclie(52440...

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le (chl528) – Homework 9 – Sutcliffe – (52440) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. A NOTE ON CELL DIAGRAMS: There is no good explanation for this but 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 reac- tion, and everthing on the RIGHT of the || is the CATHODIC reaction. Then for each of these, find a reduction half reaction in ta- ble 1.1 that includes all of the items in your anodic or cathodic reaction, and use that to write down your two half reactions. Unless Pt is listed on the far left or right; in that case 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. oxidation takes place at the cathode. 2. electrical energy is used to reverse spon- taneous chemical reactions. 3. oxidation and reduction take place at the same time but at different electrodes. cor- rect 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 cathode? 1. the solid copper electrode correct 2. the solid zinc electrode 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) Reduction occurs at the cathode. In this cell the reduction half reaction is Cu 2+ (aq) + 2 e Cu(s) Cu 2+ cations are attracted to the solid Cu electrode where they are reduced to Cu(s). 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. + 0.22 V correct 2. + 0.46 V 3. - 0.46 V
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le (chl528) – Homework 9 – Sutcliffe – (52440) 2 4. - 0.22 V 5. - 0.12 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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