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# #27 Key

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### #27 Key

1. 1. KEY GENERAL CHEMISTRY-II (1412) S.I. # 27 1. A voltaic cell is constructed where one electrode compartment consists of a silver strip placed in a solution of AgNO3, and the other has an iron strip placed in a solution of FeCl2. The overall cell reaction is Fe (s) + 2 Ag+ (aq)  Fe2+ (aq) + 2 Ag(s) a) What is being oxidized, and what is being reduced? Fe is oxidized, Ag is reduced b) Write the half reactions that occur in two electrode compartments. Ag+ + 1e-  Ag; Fe  Fe2+ + 2e- c)Which electrode is the anode, and which is the cathode? Indicate the signs of the electrode Fe is the anode and Ag is the cathode Fe is negative and Ag is positive d)Do the electrons flow from the silver electrode to the iron electrode, or from the iron to the silver? Electrons flow from the Fe(-) electrode toward the Ag(+) electrode. e) In which directions do the cations and anions migrate through the solution? Cations migrate toward the Ag cathode; anions migrate toward the Fe anode. #20.23 2. Based on the information in appendix E, which is a more favorable process, the reduction of Ag+(aq) to Ag(s) or the reduction of Sn2+(aq) to Sn(s)? The reduction of Ag+ is much more energetically favorable because it has a substantially more positive Ereduction (0.799 V) than the reduction of Sn2+ (-0.136 V). 3. Indicate whether each of the following statements is true or false. a. If something is reduced, it is formally losing electrons . ____F- ______ b. A reducing agent gets oxidized as it reacts. ____T______ c. Oxidizing agents can convert CO into CO2. ____T______
2. 2. KEY oxidation can be thought of as a gain of oxygen atoms 4. Hydrazine (N2H4) and dinitrogen tetroxide (N2O4) forma s self-igniting mixture that has been used as a rocket propellant. The reaction products are N2 and H2O. a. Write a balanced chemical equation for this reaction 2N2H4(g) + N2O4(g)  3N2(g) + 4H2O(g) b. What is being oxidized, and what is being reduced? N2H4 is oxidized; N2O4 is reduced c. Which substance serves as the reducing agent and, which as the oxidizing agent? N2O4 serves as the oxidizing agent and is reduced, N2H4 serves as the reducing agent and is oxidized. 5. Which electrode of a voltaic cell, the cathode or the anode, corresponds to the higher potential energy for the electrons? The anode has the higher potential energy for electrons. To achieve a lower potential energy, electrons flow from the anode to the cathode. 6. What are the units for electrical potential? How does this unit relate to energy expressed in joules? The units of electrical potential are volts. A potential of one volt imparts one joule of energy to coulomb of charge. 7. What is special about a standard cell potential? A standard cell potential describes the potential of an electrochemical cell where all components are present at standard conditions; elements in their standard states, gases at 1 atm pressure and 1M aqueous solutions. 8. Write the half-reaction that occurs at a hydrogen electrode in acidic aqueous solution when it serves as the cathode of a voltaic cell. 2H+ (aq) + 2e-  H2(g)