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Unit One - Redox and Electrochemistry Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. F = 96500 C/mol ____ 1. In which of the following compounds does nitrogen have the highest oxidation number? a. d. b. e. c. ____ 2. Which of the following equations does not represent an oxidation-reduction reaction? a. + + ____ ____ ____ b. + c. + d. + e. + + + 3. Experiments were performed with four strips of metals A, B, C, and D, and their corresponding nitrate solutions , , , and . Metal was placed in each of the solutions and reactions were observed only in solutions containing and ions. Metal B did not react in any of the solutions. Metal C reacted in the solution containing ions, but was not tested in the other solutions. A list of the metals in order of decreasing strength as reducing agents (strongest reducing agent is listed first) is a. B A D C d. D A C B b. C B D A e. B C A D c. C D A B 4. Consider the following oxidation-reduction reaction: Which of the following statements about this oxidation-reduction process is true? a. iodine is oxidized and potassium is reduced b. iodine is reduced and potassium is oxidized c. potassium is oxidized and chlorine is reduced d. chlorine is oxidized and hydrogen is reduced e. iodine is both oxidized and reduced 5. Which of the following half-reaction equations are balanced? I. II. III. IV. V. ____ a. I and II d. III and V b. II and IV e. all are balanced c. I and III 6. The following two half-reactions are involved in a galvanic cell: ____ At standard conditions, what species are produced at each electrode? a. is produced at the cathode and at the anode b. is produced at the cathode and at the anode c. is produced at the anode and at the cathode d. is produced at the cathode and at the anode e. is produced at the cathode and at the anode 7. Given the standard reduction potentials for the following half-reactions: What is for the reaction ? a. +0.05 V b. +0.43 V c. +1.11 V d. +1.20 V e. +1.88 V Completion Complete each sentence or statement. 8. The function of a salt bridge in a galvanic cell is to provide a pathway for the migration of ______________________________ between the two half-cells. 9. When an atom gains an electron, it is acting as a(n) ____________________ agent. 10. While an electrochemical cell is operating, the anions move internally toward the ____________________. 11. A galvanic cell consisting of mercury and lead in like 1.0 M nitrate solutions would have which metal as the anode? Short Answer - Knowledge (5 marks) 12. Will a reaction take place if a strip of zinc metal is placed in a solution of lead (II) sulfate? Justify your answer. (2 marks) 13. Calculate for the following equation: (2 marks) Decide whether the equation represents a spontaneous or a nonspontaneous reaction at standard conditions. 14. What is the direction of the electron flow in the external circuit of an electrochemical cell while the cell is operating? (1 mark) Problem - Inquiry (14 marks) 15. Balance the following equation by the half-reaction method and fill in the oxidation and reduction half reactions on the appropriate line. (4 marks) MnO41- + I2 + H1+ --> MnO2 + IO31Essay 16. Balance the following redox reaction by the oxidation number method. Clearly label the oxidation and reduction steps. (3 marks) 17. What are the problems associated with using the hydrogen fuel cell in electric cars? (3 marks) Unit One - Redox and Electrochemistry Answer Section MULTIPLE CHOICE 1. ANS: STA: 2. ANS: STA: 3. ANS: STA: 4. ANS: STA: 5. ANS: STA: 6. ANS: STA: 7. ANS: STA: D EL1.01 C EL1.01 C EL2.02 E EL1.01 D EL2.03 B EL1.02 B EL1.03 PTS: 1 REF: K/U OBJ: 9.1 PTS: 1 REF: K/U OBJ: 9.1 PTS: 1 REF: C OBJ: 9.3 PTS: 1 REF: K/U OBJ: 9.1 PTS: 1 REF: C OBJ: 9.2 PTS: 1 REF: K/U OBJ: 9.5 PTS: 1 REF: K/U OBJ: 9.3 REF: K/U OBJ: 9.5 STA: EL1.02 PTS: 1 10. ANS: anode REF: K/U OBJ: 9.3 STA: EL1.01 PTS: 1 11. ANS: lead REF: C OBJ: 10.1 STA: EL2.04 COMPLETION 8. ANS: migration of ions PTS: 1 9. ANS: oxidizing PTS: 1 SHORT ANSWER 12. ANS: Oxidation half-reaction: Reduction half-reaction: Overall reaction: for the overall reaction is positive. Thus a zinc strip will react spontaneously with lead (II) sulfate solution. PTS: 1 13. ANS: REF: C OBJ: 9.3 STA: EL2.05 Reduction half-reaction: Oxidation half-reaction: Overall reaction: for the overall reaction is positive, thus the reaction is spontaneous as written. PTS: 1 REF: C OBJ: 9.3 STA: EL2.05 14. ANS: The direction of the electron flow in an electrolytic cell is always from the anode to the cathode of the cell. PTS: 1 REF: K/U OBJ: 10.1 STA: EL1.02 PROBLEM 15. ANS: a PTS: 1 ESSAY 16. ANS: +4 2 +1 +3 2 +1 +6 2 +2 +6 2 +4 2 +1 2 The change in the oxidation number of the oxidized element C = (+4) – (+3) = +1 The change in the oxidation number of the reduced element Mn = (+2) (+4) = –2 The lowest common multiple of 1 and 2 is 2. Thus in the balanced reaction two carbon atoms are needed for every manganese atom. The increase and decrease in oxidation numbers will then be two for both. The partially balanced equation is: The remaining coefficients can be balanced by inspection and the balanced equation is: PTS: 1 REF: C OBJ: 9.2 STA: EL2.03 17. ANS: - The high cost of the hydrogen fuel cell. - the storage of hydrogen gas on board the vehicle presents safety concerns due to the flammable nature of hydrogen. - Where would the hydrogen gas (the cell fuel) come from? Electrolysis of water produces hydrogen at a high cost. - The distribution of hydrogen at retail outlets is associated with storage and handling hazards. PTS: 1 REF: MC OBJ: 9.4 STA: EL3.01