CHAPTER 5 REVIEW 1. The following represents the process used to produce iron from iron III oxide: Fe 2 O 3 + 3CO 2Fe + 3CO 2 What is the reducing agent in this process? A. Fe B. CO C. CO 2 D. Fe 2 O 3 2. Consider the following reaction: 2HNO 2 + 2I - + 2H + 2NO + I 2 +2H 2 O The oxidation number for each nitrogen atom A. increases by 1 B. increases by 2 C. decreases by 1 D. decreases by 2 3. Which of the following reactions is spontaneous? A. 2I - + Ag Ag + + I 2 B. Co 2+ + Cu Co + Cu 2+ C. Cu 2+ + Pb Pb 2+ + Cu D. Ni2 + + 2Ag 2Ag + + Ni 4. Consider the following redox reaction for a lead-acid storage cell: Pb + PbO 2 + 4H + + 2SO 4 2PbSO 4 + 2H 2 O The balanced, reduction half reaction is A. Pb + SO 4 2PbSO 4 + 2e - B. Pb + 2H + + SO 4 PbSO 4 + 2H 2 O + 2e - C. PbO 2 + 4H + + SO 4 + 2e - 2PbSO 4 + 2H 2 O D. PbO 2 + 2SO 2 4 + 2H 2 O + 2e - PbSO 4 + 2OH - 5. Consider the following reaction: Cd 2+ (aq) + Zn (s) Cd (s) + Zn 2+ (aq) The potential for the reaction is +0.36 V. What is the reduction potential for the cadmium ion? A. -1.12 V C. +0.40 V B. -0.40 V D. +1.12 V 6. Which of the following involves a nonspontaneous redox reaction? A. fuel cell B. electroplating C. redox titration D. carbon dry cell 7. Consider the following redox reaction: - 2MnO 4 + 16H + + 5Sn 2+ 2Mn 2+ + 8H 2 O + 5Sn 4+ In a redox titration, 0.60 mole of KMnO 4 reacts completely with a solution of Sn(NO 3 ) 2. How many moles of Sn(NO 3 ) 2 were present in the solution? A. 0.024 moles B. 0.060 moles C. 1.5 moles D. 0.30 moles 1
8. Which of the following is not a redox reaction? A. Cu + Br 2 CuBr 2 B. CO + H 2 O CO 2 + H 2 C. CH 4 + H 2 O CO 2 + 2H 2 O D. NaOH + HCl NaCl + H 2 O 9. What is the minimum voltage required to form nickel from an aqueous solution of NiI 2 using inert electrodes? A. 0.26 V B. 0.28 V C. 0.54 V D. 0.80 V 10. What substances are formed at the anode and cathode during electrolysis of molten sodium chloride? Anode Cathode A. O 2 H 2 B. N a Cl 2 C. Cl 2 H 2 D. Cl 2 Na 11. A solution containing an unknown cation reacts spontaneously with both zinc and copper. The unknown cation is A. 1.0 M H + C. 1.0 M Sr 2+ B. 1.0 M Ag + D. 1.0 M Mn 2+ 12. Which of the following half-reactions are balanced? A. ClO - + H 2 O + e - Cl 2 + 2OH - B. 2ClO - + H 2 O + 2e - Cl 2 + 3OH - C. 2ClO - + 2H 2 O + 2e - Cl 2 + 4OH - D. 2ClO - + 2H 2 O Cl 2 + 4OH - + 2e - 13. Which of the following is a spontaneous redox reaction? A. Ag + + I - AgI B. Ag + + Fe 2+ Ag + Fe 3+ C. 3Ag + + Au 3Ag + Au 3+ D. 2Ag + + Ni 2+ 2Ag + Ni 14. Salting the roads during the winter increases the amount of corrosion of cars. The is because the salt A. reacts with the iron B. provides an electrolyte C. acts as a reducing agent D. acts as an oxidizing agent 2
Consider the following electrochemical cell for the next five questions. voltmeter 1.0 M KCl Cu Ni 1M Cu(NO 3) 2 1M Ni(NO 3) 2 15. The half-reaction that occurs at the anode is A. Ni N 2+ + 2e - B. Ni 2+ 2e - + Ni C. Cu Cu 2+ + 2e - D. Cu 2+ 2e - + Cu 16. The half-reaction that occurs at the cathode is A. Ni N 2+ + 2e - B. Ni 2+ + 2e - Ni C. Cu Cu 2+ + 2e - D. Cu 2+ + 2e - Cu 17. The cell potential or E o is A. 0.41 V B. 0.78 V C. 0.34 V D. 0.60 V 18. The following ions migrate to the Cu electrode A. K + Cu 2+ Ni 2+ B. Cu 2+ Ni 2+ C. Cl - - NO 3 D. Cl - - NO 3 2e - 19. The electrons flow A. through the salt bridge from Cu to Ni B. through the salt bridge from Cu to Ni C. through the wire from Cu to Ni D. through the wire from Ni to Cu 20. Which of the following will not react spontaneously with 1.0 M HCl? A. tin B. lithium C. mercury D. magnesium 3
21. Which of the following can be produced by electrolysis from a 1.0 M aqueous solution containing its ion? A. nickel B. sodium C. aluminum D. magnesium 22. In order for an electrolytic cell to operate, it must have A. a voltmeter. B. a salt bridge. C. a power supply. D. an aqueous solution. 23. In the electrolysis of molten ZnCl 2 using carbon electrodes, the reaction that occurs at the anode is A. Zn Zn 2+ + 2e - B. Zn 2+ + 2e - Zn C. 2Cl - Cl 2 + 2e - D. Cl 2 + 2e - 2Cl - 24. In the electrolysis of aqueous zinc chloride, the half-reaction at the cathode is A. Cl 2 + 2e - 2Cl - C. Zn 2+ + 2e- Zn B. 2Cl - Cl 2 + 2e - D. Zn Zn 2+ + 2e - 25. The corrosion of iron can be prevented by attaching a piece of A. Mn B. Cu C. Pb D. Sn 26. The oxidation number of carbon in CaC 2 O 4 is A. +2 B. +3 C. +4 D. +6 27. To plate a nickel coin with copper, A. the nickel coin must be the cathode. B. the cathode must be made out of copper C. the electrons must flow to the anode D. the solution must contain nickel ions 4
Consider the following electrochemical cell for the next five questions. voltmeter 1.0 M KNO 3 Cu Zn 1M Cu(NO 3) 2 1M Zn(NO 3) 2 28. Which of the following statements apply to this electrochemical cell? I II III Electrons flow through the wire toward the copper electrode. The copper electrode increases in mass. Anions move toward the Zn half-cell. A. I and II only B. I and III only C. II and III only D. I, II, and III 29. The balanced equation for the overall reaction is A. Zn + Cu 2+ Cu + Zn 2+ B. Cu + Zn 2+ Zn + Cu 2+ C. Zn 2+ + Cu Cu 2+ + Zn D. Cu + Zn Zn 2+ + Cu 2+ 30. At equilibrium the voltage of the above cell is A. -1.10 V B. 0.00 V C. +0.42 V D. +1.10 V 31. This redox reaction occurs because A. Zn is a stronger oxidizing agent than Cu B. Zn is a stronger reducing agent than Cu C. Zn 2+ is a stronger oxidizing agent than Cu 2+ D. Zn 2+ is a weaker reducing agent than Cu 2+ 32. The initial cell voltage at 25 o C is A. -1.10 V B. +1.10 V C. +0.91 V D. +0.86 V 5
33. Consider the following redox reaction: Co 2+ (aq) + 2Ag (s) 2Ag + (aq) + Co (s) The reaction is A. spontaneous and E o is positive B. spontaneous and E o is negative C. non-spontaneous and E o is positive D. non-spontaneous and E o is negative 34. When MnO 4 - reacts to form Mn 2+, the manganese in MnO 4 - is A. reduced as its oxidation number increases B. reduced as its oxidation number decreases C. oxidized as its oxidation number increases D. oxidized as its oxidation number decreases 35. The electrolyte used in the alkaline battery is A. KCl B. NaOH C. H 2 SO 4 D. KOH 36. The electrolyte used in an automobile battery is A. KCl B. NaOH C. H 2 SO 4 D. KOH 37. The anode used in the commercial production of Aluminum is A. C B. Pt C. Al D. AL 2 O 3 38. The anode and cathode used in the electrorefining of impure lead to pure lead are Anode Cathode A. Pure Pb Impure Pb B. Impure Pb Pure Pb C. Pb 2+ Pb D. Pb Pb 2+ 39. The anode in the Zinc or common dry cell is A. C B. Zn C. Mg D. KOH 40. Which of the following are electrolytic cells I II Electrowinning Electroplating III IV Charging a car battery Fuel cell A. I and II only B. I, II, and III only C. II and II only D. I, II, III, and IV 6
Subjective 1. Balance the following in basic solution. MnO 4 - + C 2 O 4 MnO 2 + CO 2 (basic) 2. Consider the electrolysis of 1.0 M H 2 SO 4 using platinum electrodes. a) Write the oxidation half-reaction b) Write the reduction half-reaction c) Write the overall reaction and determine the minimum theoretical voltage required. Consider the following diagram for the electrorefinning of lead. Power Source Pure Pb Impure Pb a) On the diagram, label the anode and cathode. b) Write the formula for a suitable electrolyte c) Write the equation for the reduction half-reaction. 7
4. Describe two chemically different methods that can be used to prevent corrosion of iron and explain why each method works. Method 1: Explanation: Method 2: Explanation: 5. The data below were obtained in a redox titration of a 25.00 ml sample containing Sn 2+ ions using 0.125 M KMnO 4 according to the following reaction: 2MnO 4 - + 16H + + 5Sn 2+ 2Mn 2+ + 8H 2 O + 5Sn 4+ Volume of KMnO 4 used (ml) Trial 1 Trial 2 Trial 3 Initial burette reading 2.00 13.80 24.55 Final burette reading 13.80 24.55 35.32 6. A student wanted to electroplate a coin with copper. a) Identify a suitable anode b) Identify an appropriate electrolyte c) To which battery terminal (positive or negative) should the coin be connected? 7. Consider the electrolysis of molten magnesium chloride. a) Identify the product at the anode. b) Write the equation for the reduction half-reaction. 8
c) Write the equation for the overall reaction. 8. Consider the following electrochemical cell. voltmeter 1.0 M KNO 3 Sn Mn 1M Sn(NO 3) 2 1M MnNO 3) 2 a) Write the anode reaction b) Write the cathode reaction c) Write the overall reaction and determine the initial cell potential (E o ). d) Explain in words how the electrons move through the cell. e) List all of the ions that migrate toward the Sn electrode. f) Which electrode loses mass? g) What is the purpose of the salt bridge? h) What is the cell potential once equilibrium is achieved 9
UNIT 5 REVIEW - SOLUTIONS 1. The following represents the process used to produce iron from iron III oxide: Fe 2 O 3 + 3CO 2Fe + 3CO 2 What is the reducing agent in this process? A. Fe B. CO C. CO 2 D. Fe 2 O 3 2. Consider the following reaction: 2HNO 2 + 2I - + 2H + 2NO + I 2 +2H 2 O The oxidation number for each nitrogen atom A. increases by 1 B. increases by 2 C. decreases by 1 D. decreases by 2 3. Which of the following reactions is spontaneous? A. 2I - + Ag Ag + + I 2 B. Co 2+ + Cu Co + Cu 2+ C. Cu 2+ + Pb Pb 2+ + Cu D. Ni2 + + 2Ag 2Ag + + Ni 4. Consider the following redox reaction for a lead-acid storage cell: Pb + PbO 2 + 4H + + 2SO 4 2PbSO 4 + 2H 2 O The balanced, reduction half reaction is A. Pb + SO 4 2PbSO 4 + 2e - B. Pb + 2H + + SO 4 PbSO 4 + 2H 2 O + 2e - C. PbO 2 + 4H + + SO 4 + 2e - 2PbSO 4 + 2H 2 O D. PbO 2 + 2SO 2 4 + 2H 2 O + 2e - PbSO 4 + 2OH - 5. Consider the following reaction: Cd 2+ (aq) + Zn (s) Cd (s) + Zn 2+ (aq) The potential for the reaction is +0.36 V. What is the reduction potential for the cadmium ion? A. -1.12 V B. -0.40 V C. +0.40 V D. +1.12 V 6. Which of the following involves a nonspontaneous redox reaction? A. fuel cell B. electroplating C. redox titration D. carbon dry cell - 7. Consider the following redox reaction: 2MnO 4 + 16H + + 5Sn 2+ 2Mn 2+ + 8H 2 O + 5Sn 4+ 10
In a redox titration, 0.60 mole of KMnO 4 reacts completely with a solution of Sn(NO 3 ) 2. How many moles of Sn(NO 3 ) 2 were present in the solution? A. 0.024 moles B. 0.060 moles C. 1.5 moles D. 0.30 moles 8. Which of the following is not a redox reaction? A. Cu + Br 2 CuBr 2 B. CO + H 2 O CO 2 + H 2 C. CH 4 + H 2 CO 2 + 2H 2 O D. NaOH + HCl NaCl + H 2 O 9. What is the minimum voltage required to form nickel from an aqueous solution of NiI 2 using inert electrodes? A. 0.26 V B. 0.28 V C. 0.54 V D. 0.80 V 10. What substances are formed at the anode and cathode during electrolysis of molten sodium chloride? Anode Cathode A. O 2 H 2 B. N a Cl 2 C. Cl 2 H 2 D. Cl 2 Na 11. A solution containing an unknown cation reacts spontaneously with both zinc and copper. The unknown cation is A. 1.0 M H + B. 1.0 M Ag + C. 1.0 M Sr 2+ D. 1.0 M Mn 2+ 11
12. Which of the following half-reactions are balanced? A. ClO - + H 2 O + e - Cl 2 + 2OH - B. 2ClO - + H 2 O + 2e - Cl 2 + 3OH - C. 2ClO - + 2H 2 O + 2e - Cl 2 + 4OH - D. 2ClO - + 2H 2 O Cl 2 + 4OH - + 2e - 13. Which of the following is a spontaneous redox reaction? A. Ag + + I - AgI B. Ag + + Fe 2+ Ag + Fe 3+ C. 3Ag + + Au 3Ag + Au 3+ D. 2Ag + + Ni 2+ 2Ag + Ni 14. Salting the roads during the winter increases the amount of corrosion of cars. The is because the salt A. reacts with the iron B. provides an electrolyte C. acts as a reducing agent D. acts as an oxidizing agent Consider the following electrochemical cell for the next five questions. voltmeter 1.0 M KCl Cu Ni 1M Cu(NO 3) 2 1M Ni(NO 3) 2 15. The half-reaction that occurs at the anode is A. Ni Ni 2+ + 2e - B. Ni 2+ 2e - + Ni C. Cu Cu 2+ + 2e - D. Cu 2+ 2e - + Cu 16. The half-reaction that occurs at the cathode is A. Ni N 2+ + 2e - B. Ni 2+ + 2e - Ni 12
C. Cu Cu 2+ + 2e - D. Cu 2+ + 2e - Cu 17. The cell potential or E o is A. 0.41 V B. 0.78 V C. 0.34 V D. 0.60 V 18. The following ions migrate to the Cu electrode A. K + Cu 2+ Ni 2+ B. Cu 2+ Ni 2+ C. Cl - - NO 3 D. Cl - - NO 3 2e - 19. The electrons flow A. through the salt bridge from Cu to Ni B. through the salt bridge from Cu to Ni C. through the wire from Cu to Ni D. through the wire from Ni to Cu 20. Which of the following will not react spontaneously with 1.0 M HCl? A. tin B. lithium C. mercury D. magnesium 21. Which of the following can be produced by electrolysis from a 1.0 M aqueous solution containing its ion? A. nickel B. sodium C. aluminum D. magnesium 22. In order for an electrolytic cell to operate, it must have A. a voltmeter. B. a salt bridge. C. a power supply. D. an aqueous solution. 23. In the electrolysis of molten ZnCl 2 using carbon electrodes, the reaction that occurs at the anode is 13
A. Zn Zn 2+ + 2e - B. Zn 2+ + 2e - Zn C. 2Cl - Cl 2 + 2e - D. Cl 2 + 2e - 2Cl - 24. In the electrolysis of aqueous zinc chloride, the half-reaction at the anode is A. Cl 2 + 2e - 2Cl - B. 2Cl - Cl 2 + 2e - C. Zn 2+ + 2e- Zn D. Zn Zn 2+ + 2e - 25. The corrosion of iron can be prevented by attaching a piece of A. Mn B. Cu C. Pb D. Sn 26. The oxidation number of carbon in CaC 2 O 4 is A. +2 B. +3 C. +4 D. +6 27. To plate a nickel coin with copper, A. the nickel coin must be the cathode. B. the cathode must be made out of copper C. the electrons must flow to the anode D. the solution must contain nickel ions Consider the following electrochemical cell for the next five questions. voltmeter 1.0 M KNO 3 Cu Zn 1M Cu(NO 3) 2 1M Zn(NO 3) 2 14
28. Which of the following statements apply to this electrochemical cell? I II III Electrons flow through the wire toward the copper electrode. The copper electrode increases in mass. Anions move toward the Zn half-cell. A. I and II only B. I and III only C. II and III only D. I, II, and III 29. The balanced equation for the overall reaction is A. Zn + Cu 2+ Cu + Zn 2+ B. Cu + Zn 2+ Zn + Cu 2+ C. Zn 2+ + Cu Cu 2+ + Zn D. Cu 2+ + Zn Zn 2+ + Cu 30. At equilibrium the voltage of the above cell is A. -1.10 V B. 0.00 V C. +0.42 V D. +1.10 V 31. This redox reaction occurs because A. Zn is a stronger oxidizing agent than Cu B. Zn is a stronger reducing agent than Cu C. Zn 2+ is a stronger oxidizing agent than Cu 2+ D. Zn 2+ is a weaker reducing agent than Cu 2+ 32. The initial cell voltage at 25 o C is A. -1.10 V B. +1.10 V C. +0.91 V D. +0.86 V 33. Consider the following redox reaction: Co 2+ (aq) + 2Ag (s) 2Ag + (aq) + Co (s) The reaction is A. spontaneous and E o is positive B. spontaneous and E o is negative C. non-spontaneous and E o is positive D. non-spontaneous and E o is negative 34. When MnO 4 - reacts to form Mn 2+, the manganese in MnO 4 - is 15
A. reduced as its oxidation number increases B. reduced as its oxidation number decreases C. oxidized as its oxidation number increases D. oxidized as its oxidation number decreases 35. The electrolyte used in the alkaline battery is A. KCl B. NaOH C. H 2 SO 4 D. KOH 36. The electrolyte used in an automobile battery is A. KCl B. NaOH C. H 2 SO 4 D. KOH 37. The anode used in the commercial production of Aluminum is A. C B. Pt C. Al D. AL 2 O 3 38. The anode and cathode used in the electrorefining of impure lead to pure lead are Anode Cathode A. Pure Pb Impure Pb B. Impure Pb Pure Pb C. Pb 2+ Pb D. Pb Pb 2+ 39. The anode in the LeClanche or common dry cell is A. C B. Zn C. Mg D. KOH 40. Which of the following are electrolytic cells I II III Electrowinning Electroplating Charging a car battery 16
IV Fuel cell A. I and II only B. I, II, and III only C. II and II only D. I, II, III, and IV 17
Subjective 1. Balance the following in basic solution. MnO 4 - + C 2 O 4 MnO 2 + CO 2 (basic) 2(MnO 4 - + 4H + + 3e - MnO 2 + 2H 2 O ) 3(C 2 O 4 2CO 2 + 2e - ) Acid: 2MnO 4 - Basic: 2MnO 4 - + 3C 2 O 4 + 3C 2 O 4 + 8H + 2MnO 2 + 6CO 2 + 4H 2 O + 4H 2 O 2MnO 2 + 6CO 2 + 8OH - 2. Consider the electrolysis of 1.0 M H 2 SO 4 using platinum electrodes. a) Write the oxidation half-reaction H 2 O 1/2O 2 + 2H + + 2e - E o = -0.82 V b) Write the reduction half-reaction SO 4 + 4H + + 2e - H 2 SO 3 + H 2 O E o = +0.17 V c) Write the overall reaction and determine the minimum theoretical voltage required. SO 4 + 4H + 1/2O 2 + 2H + + H 2 SO 3 E o = -0.65 V MTV = +0.65 V 18
3. Consider the following diagram for the electrorefinning of lead. Power Source Cathode Pure Pb Anode Impure Pb a) On the diagram, label the anode and cathode. b) Write the formula for a suitable electrolyte Pb(NO 3 ) 2 c) Write the equation for the reduction half-reaction. Pb 2+ + 2e - Pb (s) 4. Describe two chemically different methods that can be used to prevent corrosion of iron and explain why each method works. Method 1: Explanation: Painting Prevents reactants H 2 O and O 2 from contacting the iron Method 2: Attach some Zn Explanation: Fe is forced to be the cathode and cannot oxidize 5. The data below were obtained in a redox titration of a 25.00 ml sample containing Sn 2+ ions using 0.125 M KMnO 4 according to the following reaction: - 2MnO 4 + 16H + + 5Sn 2+ 2Mn 2+ + 8H 2 O + 5Sn 4+ Volume of KMnO 4 used (ml) 19
Trial 1 Trial 2 Trial 3 Initial burette reading 2.00 13.80 24.55 Final burette reading 13.80 24.55 35.32 11.80 10.75 10.77 Average last two to get 10.76 ml Calculate the [Sn 2+ ] [Sn 2+ ] = 0.01076 L x 0.125 mole x 5 moles Sn 2+ 1 L - 2 moles MnO 4 0.0250 L = 0.135 M 6. A student wanted to electroplate a coin with copper. a) Identify a suitable anode Cu b) Identify an appropriate electrolyte CuSO 4 c) To which battery terminal (positive or negative) should the coin be connected? Negative 7. Consider the electrolysis of molten magnesium chloride. a) Identify the product at the anode. Cu 2+ b) Write the equation for the reduction half-reaction. Mg 2+ + 2e - Mg (s) c) Write the equation for the overall reaction. Mg 2+ + 2Cl - Mg (s) + Cl 2 8. Consider the following electrochemical cell. voltmeter Sn 1.0 M KNO 3 Mn 20
Cathode Anode a) Write the anode reaction Sn 2+ + 2e - Sn b) Write the cathode reaction Mn Mn 2+ + 2e - c) Write the overall reaction and determine the initial cell potential (E o ). Sn 2+ + Mn Mn 2+ + Sn d) Explain in words how the electrons move through the cell. From anode Mn to cathode Sn e) List all of the ions that migrate toward the Sn electrode. Sn 2+ Mn 2+ K + f) Which electrode loses mass? Anode Sn g) What is the purpose of the salt bridge? To allow cations and anions to flow from one half cell to the other h) What is the cell potential once equilibrium is achieved? 0.00 v 21