1. When the redox equation CHEMISTRY 13 Electrochemistry Supplementary Problems MnO 4 (aq) + H + (aq) + H 3 AsO 3 (aq) Mn 2+ (aq) + H 3 AsO 4 (aq) + H 2 O(l) is properly balanced, the coefficients will be: MnO 4 H + H 3 AsO 3 Mn 2+ H 3 AsO 4 H 2 O A. 1 3 10 1 1 1 B. 2 14 10 2 10 15 C. 4 12 10 4 10 6 D. 1 3 2 1 2 1 E. 2 6 5 2 5 3 2. When the following reaction that takes place in acidic solution is balanced, the number of protons (H + (aq)) that will be involved in the balanced equation is: Cr 2 O 2 7 (aq) + I (aq) Cr 3+ (aq) + IO 3 (aq) A. 2 B. 4 C. 6 D. 8 E. None of the above. 3. When the following reaction that takes place in basic solution is balanced, the number of hydroxide ions (OH (aq)) that will be involved in the balanced equation is: CN (aq) + MnO 4 (aq) CNO (aq) + MnO 2 (s) A. 2 B. 4 C. 6 D. 8 E. None of the above. 4. Which is the best reducing agent in the following set? A. Cl (aq) B. Fe(s) C. Fe 3+ (aq) D. Fe 2+ (aq) E. Cl 2 (g)
5. Arrange the following oxidizing agents in order of increasing oxidizing power: I 2 (s), IO 3 - (aq), F 2 (g), PbO 2 (s), Na + (aq), Zn 2+ (aq) A. I 2 < Zn 2+ < IO 3 < PbO 2 < Na + < F 2 B. F 2 < PbO 2 < IO 3 < I 2 < Zn 2+ < Na + C. I 2 < IO 3 < PbO 2 < F 2 < Zn 2+ < Na + D. Na + < Zn 2+ < I 2 < IO 3 < PbO 2 < F 2 E. I 2 < IO 3 < PbO 2 < F 2 < Na + < Zn 2+ 6. The oxidizing agent in this cell is? 2 Ag + (1.0 M) + Ni(s) Ni 2+ (1.0 M) + 2 Ag(s) A. Ag B. Ag + C. Ni 2+ D. Ni E. none of the above 7. Calculate E o (in volts) for a cell in which the overall reaction is: A. 0.93 B. 0.67 C. 1.73 D. 1.47 E. 0.52 Pb(s) + 2 Ag + (aq) Pb 2+ (aq) + 2 Ag(s) 8. What is the voltaic cell with the highest standard emf that could he constructed from the metals: copper, iron, nickel, silver and zinc? A. Ag Ag + + e ; Zn 2+ + 2e Zn B. Zn Zn 2+ + 2e ; Ag + + e Ag C. Ni Ni 2+ + 2e ; Cu 2+ + 2e Cu D. Fe Fe 2+ + 2e ; Ni 2+ + 2e Ni E. Zn Zn 2+ + 2e ; Cu 2+ + 2e Cu 9. The purpose of the salt bridge in an electrochemical cell is to. A. maintain electrical neutrality in the half-cells via migration of ions. B. provide a source of ions to react at the anode and cathode. C. provide oxygen to facilitate oxidation at the anode. D. provide a means for electrons to travel from the anode to the cathode. E. provide a means for electrons to travel from the cathode to the anode.
10. Consider the following cell: Which of the following statements is false? A. Electrons will flow from the cobalt strip to the tin strip. B. The tin electrode will grow bigger with time. C. NO 3 ions will move out of the salt bridge into the left hand compartment. D. The Co 2+ (aq) concentration in the right hand compartment will increase with time. E. Electrons will flow through the wire. 11. The value of E o for the following reaction is 0.63 V. What is the value of E for this reaction when the concentration of Zn 2+ is 0.0002 M and the concentration of Pb 2+ is 1.0 M? A. 0.85 V B. 0.74 V C. 0.52 V D. 0.41 V E. 0.30 V Pb 2+ (aq) + Zn(s) Zn 2+ + Pb(s) 12. Which of the following are true for a voltaic cell? I. G o > 0 II. Oxidation will occur at the anode. III. At equilibrium, E cell will equal 0. A. I only B. II only C. I and II D. II and III E. I and III
13. What is the concentration of the Pb(NO 3 ) 2 in the voltaic cell pictured above when E cell = 0.524V at room temperature? A. 1.00 M B. 1.92 x 10-4 M C. 0.110 M D. 52.0 M E. 1.39 x 10-2 M 14. A voltaic cell is based on the following spontaneous redox reaction. 2 Ag + (aq) + Ni(s) 2 Ag(s) + Ni 2+ (aq) What is the cell voltage when the conditions are non-standard with [Ag + ] = 0.01 M, [Ni 2+ ] =2.0 M? A. 0.95V B. 0.83V C. 1.05V D. 1.21V E. 0.76 V 15. What is the equilibrium constant for the following reaction at 25 o C A. 2 x 10 5 B. 1 x 10 21 C. 3 x 10 10 D. l x 10 21 E. 3 x 10 30 Zn(s) + Sn 2+ (aq) Zn 2+ (aq) + Sn(s)
16. The measured voltage at 25 C of a cell, in which the reaction Cd(s) + Pb 2+ (aq, 0.150 M) Pb(s) + Cd 2+ (aq, 0.0250 M) takes place, is 0.293 V. The values of K (the equilibrium constant of the reaction) and of E o are: A. 1.31 x 10 9 and 0.270 V B. 2.36 x 10 8 and 0.247 V C. 2.36 x 10 8 and 0.270 V D. 1.31 x 10 9 and 2.247 V E. None of these are correct. 17. The equilibrium constant for the following reaction at 298K is 7.676 x10 3. VO 2 + (aq) + Fe +2 (aq) + 2H + (aq) Fe +3 (aq) + VO 2+ (aq) + H 2 O(l) What is the emf of the electrochemical cell at 298K if the [Fe 3+ ] = [Fe 2+ ] =4.51x10 3 M and the [VO 2+ ] = [VO 2 + ] =0.152M while the cell is maintained at a ph =of 7? A. 0.230V B. 0.958V C. 0.414V D. 0.644V E. 0.599 V 18. Consider an electrochemical cell based on the reaction: 2H + (aq) + Sn(s) Sn 2+ (aq) + H 2 (g) Which one of the following actions would increase the measured cell potential? A. decreasing the ph in the cathode compartment B. increasing the mass and surface area of the Sn electrode C. increasing the [Sn 2+ ] in the anode compartment D. increasing the pressure of hydrogen gas in the cathode compartment E. All of the above will increase the measured cell potential.
19. Consider a voltaic cell based upon the following reaction Pb(s) + 2 H + (aq) + SO 4 2- (aq) PbSO 4 (s) + H 2 (g) E o = +0.36 V The following changes are made in an attempt to increase the voltage of the cell: (1) The area of the Pb electrode is increased. (2) The [H + (aq)] is increased. (3) The pressure of H 2 (g) is increased. The change(s) which would increase the cell voltage is (are) A. 1, 2, and 3 B. 2 only C. 3 only D. 1 only E. None of the above changes will have an effect on the cell voltage. 20. Which one of the following statements concerning the lead storage battery is false? A. The electrolyte present is aqueous H 2 SO 4. B. During charging, PbO 2 is formed at one electrode. C. In winter, a charged battery is more likely to freeze than an uncharged one. D. During discharge, PbSO 4 is formed at both electrodes. E. The amount of charge present in the battery can be guessed by measuring the density of the electrolyte. 21. Which of the following metals can be used to provide cathodic protection to prevent corrosion of iron? A. Co B. Al C. Sn D. Cd E. None of the above metals will provide cathodic protection to iron. 22. One of the differences between a voltaic cell and an electrolytic cell is that in an electrolytic cell, A. an electric current is produced by a chemical reaction. B. electrons flow towards the anode. C. a nonspontaneous reaction is forced to occur. D. O 2 gas is always produced at the cathode. E. only non-aqueous electrolyte solutions can be used.
23. When an aqueous solution which is 0.1 M in FeBr 3 and 0.1 M in CuCl 2 is electrolyzed, the initial product formed at the cathode is: A. Cl 2 (g) B. Br 2 (g) C. Fe(s) D. Cu(s) E. Fe 2+ (aq) 24. In a lecture demonstration, an aqueous solution of Pb(NO 3 ) 2 was electrolyzed at inert Pt wire electrodes. The pure metal, Pb A. deposited on the anode. B. deposited on the cathode. C. remained in the electrolyte (in solution). D. collected in the anode sludge. E. collected in the cathode sludge 25. Which of the following is the cathodic reaction in the electrolysis of aqueous NaI? A. Na + + e Na B. Na Na + + e C. 2 I I 2 + 2 e D. I 2 + 2 e 2 I E. 2 H 2 O + 2 e H 2 + 2 OH 26 A Zn 2+ (aq) solution is electrolyzed using a current of 0.60 amp. What mass of Zn(s) is plated out after 5 hours? (M.W. of Zn = 65.4) A. 6.10 x 10 2 g B. 7.32 g C. 3.66 g D. l.83 g E. 5.60 x 10 2 g 27. How many Faradays are required to reduce 1 mole of MnO 4 (aq) to MnO 2 (s)? A. 1 B. 2 C. 3 D. 4 E. 5
28. A current of 0.452 A is passed for 1.50 hour through an electrolytic cell containing molten MgCl 2. The quantity of Mg plated out will be: A. 0.154 g B. 0.307 g C. 0.614 g D. 1.540 g E. none of the answers is correct to within 5%
1. E 2. D 3. A 4. B 5. D 6. B 7. A 8. B 9. A 10. C 11. B 12. B 13. B 14. A 15. D 16. A 17. E 18. A 19. B 20. C 21. B 22. C 23. E 24. B 25. E 26. C 27. C 28. B Chem 13 Supplemental Problems Electrochemistry Answer Key