7. Which equation represents an oxidation-reduction reaction?

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1 1. Which polyatomic ion has a charge of 3? 1) chromate ion 2) oxalate ion 3) phosphate ion 4) thiocyanate ion 2. An oxidation-reduction reaction involves the 1) sharing of electrons 2) sharing of protons 3) transfer of electrons 4) transfer of protons 3. Which ion is most easily reduced? 1) Zn 2+ 2) Mg 2+ 3) Co 2+ 4) Ca Given the balanced ionic equation representing a reaction: 2Al(s) + 3Cu 2+ (aq) 2Al 3+ (aq) + 3Cu(s) Which half-reaction represents the reduction that occurs? 1) Al Al e 2) Al e Al 3) Cu Cu e 4) Cu e Cu 5. Which half-reaction equation represents the reduction of an iron(ii) ion? 1) Fe 2+ Fe 3+ + e 2) Fe e Fe 3) Fe 3+ + e Fe 2+ 4) Fe Fe e 6. Which half-reaction equation represents the reduction of a potassium ion? 1) K + + e K 2) K + e K + 3) K + K + e 4) K K + + e 7. Which equation represents an oxidation-reduction reaction? '08 to '12 Regents Exams Page 1 Only NYS Regents 1) 2) 3) 4) 8. Which balanced equation represents an oxidation-reduction reaction? 1) Ba(NO3)2 + Na2SO4 BaSO4 + 2NaNO3 2) H3PO4 + 3KOH K3PO4 + 3H2O 3) Fe(s) + S(s) FeS(s) 4) NH3(g) + HCl(g) NH4Cl(s) 9. Which balanced equation represents a redox reaction? 1) AgNO3(aq) + NaCI(aq) AgCI(s) + NaNO3(aq) 2) H2CO3(aq) H2O( ) + CO2(g) 3) NaOH(aq) + HCl(aq) NaCl(aq) + H2O( ) 4) Mg(s) + 2HCl(aq) MgCl2(aq) + H 2(g) 10. Which metal is more active than H2? 1) Ag 2) Au 3) Cu 4) Pb 11. What is the oxidation state of nitrogen in the compound NH4Br? 1) 1 2) +2 3) 3 4) What is the oxidation number of sulfur in Na2S2O3? 1) 1 2) +2 3) +6 4) Given the balanced equation representing a reaction: 2KClO3(s) 2KCl(s) + 3O2(g) The oxidation state of chlorine in this reaction changes from 1) 1 to +1 2) 1 to +5 3) + l to 1 4) +5 to 1

2 14. During which process does an atom gain one or more electrons? 1) transmutation 2) reduction 3) oxidation 4) neutralization 15. Which half-reaction correctly represents reduction? 1) Mn 4+ Mn 3+ + e 2) Mn 4+ Mn e 3) Mn 4+ + e Mn 3+ 4) Mn e Mn In a redox reaction, the total number of electrons lost is 1) less than the total number of electrons gained 2) greater than the total number of electrons gained 3) equal to the total number of electrons gained 4) equal to the total number of protons gained 17. Given the balanced equation representing a reaction: Fe2O3 + 2Al Al 2O3 + 2Fe During this reaction, the oxidation number of Fe changes from 1) +2 to 0 as electrons are transferred 2) +2 to 0 as protons are transferred 3) +3 to 0 as electrons are transferred 4) +3 to 0 as protons are transferred 18. Which balanced equation represents a redox reaction? 1) 2) 3) 4) 19. Which equation represents an oxidationreduction reaction? 1) CH4 + 2O2 CO2 + 2H2O 2) H2SO4 + Ca(OH)2 CaSO4 + 2H2O 3) MgCrO4 + BaCl2 MgCl2 + BaCrO4 4) Zn(NO3)2 + Na2CO3 2NaNO3 + ZnCO Which reaction occurs spontaneously? 1) Cl2(g) + 2NaBr(aq) Br 2( ) + 2NaCl(aq) 2) Cl2(g) + 2NaF(aq) F2(g) + 2NaCl(aq) 3) I2(s) + 2NaBr(aq) Br2( ) + 2NaI(aq) 4) I2(s) + 2NaF(aq) F2(g) + 2NaI(aq) 21. Which metal is more active than Ni and less active than Zn? 1) Cu 2) Cr 3) Mg 4) Pb 22. Which ionic equation is balanced? 1) Fe 3+ + Al Fe 2+ + Al 3+ 2) Fe Al Fe Al 3+ 3) 3Fe 3+ + Al 3Fe 2+ + Al 3+ 4) 3Fe 3+ + Al Fe Al Given the balanced equation representing a reaction: 2Fe + 3Cu 2+ 2Fe Cu When the iron atoms lose six moles of electrons, how many moles of electrons are gained by the copper ions? 1) 12 moles 2) 2 moles 3) 3 moles 4) 6 moles '08 to '12 Regents Exams Page 2 Only NYS Regents

3 24. Which statement describes where the oxidation and reduction half-reactions occur in an operating electrochemical cell? 1) Oxidation and reduction both occur at the anode. 2) Oxidation and reduction both occur at the cathode. 3) Oxidation occurs at the anode, and reduction occurs at the cathode. 4) Oxidation occurs at the cathode, and reduction occurs at the anode. 25. Which energy change occurs in an operating voltaic cell? 1) chemical to electrical 2) electrical to chemical 3) chemical to nuclear 4) nuclear to chemical 26. A voltaic cell spontaneously converts chemical energy to 1) electrical energy 2) geothermal energy 3) mechanical energy 4) nuclear energy 27. Which energy conversion occurs in a voltaic cell? 1) chemical energy to electrical energy 2) chemical energy to nuclear energy 3) electrical energy to chemical energy 4) nuclear energy to electrical energy 28. When a voltaic cell operates, ions move through the 1) anode 2) cathode 3) salt bridge 4) external circuit 29. Given the balanced ionic equation representing the reaction in an operating voltaic cell: Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s) The flow of electrons through the external circuit in this cell is from the 1) Cu anode to the Zn cathode 2) Cu cathode to the Zn anode 3) Zn anode to the Cu cathode 4) Zn cathode to the Cu anode 30. Reduction occurs at the cathode in 1) electrolytic cells, only 2) voltaic cells, only 3) both electrolytic cells and voltaic cells 4) neither electrolytic cells nor voltaic cells 31. Which reaction occurs at the cathode in an electrochemical cell? 1) combustion 2) neutralization 3) oxidation 4) reduction 32. Which energy conversion occurs in an operating electrolytic cell? 1) chemical energy to electrical energy 2) electrical energy to chemical energy 3) nuclear energy to thermal energy 4) thermal energy to nuclear energy 33. Which statement describes one characteristic of an operating electrolytic cell? 1) It produces electrical energy. 2) It requires an external energy source. 3) It uses radioactive nuclides. 4) It undergoes a spontaneous redox reaction. '08 to '12 Regents Exams Page 3 Only NYS Regents

34. The diagram below represents an operating electrochemical cell and the balanced ionic equation for the reaction occurring in the cell. 35. Which statement describes electrolysis?

4 34. The diagram below represents an operating electrochemical cell and the balanced ionic equation for the reaction occurring in the cell. 35. Which statement describes electrolysis? 1) Chemical energy is used to produce an electrical change. 2) Chemical energy is used to produce a thermal change. 3) Electrical energy is used to produce a chemical change. 4) Thermal energy is used to produce a chemical change. 36. Given the balanced equation representing a reaction occurring in an electrolytic cell: Which statement identifies the part of the cell that conducts electrons and describes the direction of electron flow as the cell operates? 1) Electrons flow through the salt bridge from the Ni(s) to the Zn(s). 2) Electrons flow through the salt bridge from the Zn(s) to the Ni(s). 3) Electrons flow through the wire from the Ni(s) to the Zn(s). 4) Electrons flow through the wire from the Zn(s) to the Ni(s). 2NaCl( ) 2Na( ) + Cl2(g) Where is Na( ) produced in the cell? 1) at the anode, where oxidation occurs 2) at the anode, where reduction occurs 3) at the cathode, where oxidation occurs 4) at the cathode, where reduction occurs '08 to '12 Regents Exams Page 4 Only NYS Regents

Base your answers to questions 37 through 40 on the information below. A student constructs an electrochemical cell during a laboratory investigation.

5 Base your answers to questions 37 through 40 on the information below. A student constructs an electrochemical cell during a laboratory investigation. When the switch is closed, electrons flow through the external circuit. The diagram and equation below represent this cell and the reaction that occurs. 37. Write a balanced half-reaction equation for the oxidation that occurs when the switch is closed. 38. Determine the number of moles of Al(s) needed to completely react with 9.0 moles of Ni 2+ (aq) ions. 39. State, in terms of energy, why this cell is a voltaic cell. 40. State the direction of electron flow through the wire when the switch is closed. '08 to '12 Regents Exams Page 5 Only NYS Regents

Base your answers to questions 41 through 43 on the information below. The diagram below represents an operating electrolytic cell used to plate silver onto a nickel key.

6 Base your answers to questions 41 through 43 on the information below. The diagram below represents an operating electrolytic cell used to plate silver onto a nickel key. As the cell operates, oxidation occurs at the silver electrode and the mass of the silver electrode decreases. 41. Identify the cathode in the cell. 42. State the purpose of the power source in the cell. 43. Explain, in terms of Ag atoms and Ag + (aq) ions, why the mass of the silver electrode decreases as the cell operates. '08 to '12 Regents Exams Page 6 Only NYS Regents

7 Base your answers to questions 44 and 45 on the information below. The diagram and balanced ionic equation below represent a voltaic cell with copper and silver electrodes and the reaction that occurs when the cell is operating. 44. Describe the direction of electron flow in the external circuit in this operating cell. 45. State the purpose of the salt bridge in this voltaic cell. 46. Explain, in terms of activity, why HCl(aq) reacts with Zn(s), but HCl(aq) does not react with Cu(s). '08 to '12 Regents Exams Page 7 Only NYS Regents

Base your answers to questions 47 through 49 on the information below. The diagram below represents an operating voltaic cell at 298 K and 1.0 atmosphere in a laboratory investigation.

8 Base your answers to questions 47 through 49 on the information below. The diagram below represents an operating voltaic cell at 298 K and 1.0 atmosphere in a laboratory investigation. The reaction occurring in the cell is represented by the balanced ionic equation below. 47. Identify the anode in this cell. 48. Determine the total number of moles of Ni 2+ (aq) ions produced when 4.0 moles of Ag + (aq) ions completely react in this cell 49. Write a balanced half-reaction equation for the reduction that occurs in this cell. '08 to '12 Regents Exams Page 8 Only NYS Regents

9 Base your answers to questions 50 through 53 on the information below. In a laboratory investigation, a student constructs a voltaic cell with iron and copper electrodes. Another student constructs a voltaic cell with zinc and iron electrodes. Testing the cells during operation enables the students to write the balanced ionic equations below. Cell with iron and copper electrodes: Cu 2+ (aq) + Fe(s) Cu(s) + Fe 2+ (aq) Cell with zinc and iron electrodes: Fe 2+ (aq) + Zn(s) Fe(s) + Zn 2+ (aq) 50. State evidence from the balanced equation for the cell with iron and copper electrodes that indicates the reaction in the cell is an oxidation-reduction reaction. 51. Identify the particles transferred between Fe 2+ and Zn during the reaction in the cell with zinc and iron electrodes. 52. Write a balanced half-reaction equation for the reduction that takes place in the cell with zinc and iron electrodes. 53. State the relative activity of the three metals used in these two voltaic cells. '08 to '12 Regents Exams Page 9 Only NYS Regents

10 Base your answers to questions 54 through 56 on the information below. A voltaic cell with magnesium and copper electrodes is shown in the diagram below. The copper electrode has a mass of 15.0 grams. When the switch is closed, the reaction in the cell begins. The balanced ionic equation for the reaction in the cell is shown below the cell diagram. After several hours, the copper electrode is removed, rinsed with water, and dried. At this time, the mass of the copper electrode is greater than 15.0 grams. 54. State the directions of electron flow through the wire between the electrodes when the switch is closed. 55. State the purpose of the salt bridge in this cell. 56. Explain, in terms of copper ions and copper atoms, why the mass of the copper electrode increases as the cell operates. Your response must include information about both copper ions and copper atoms. '08 to '12 Regents Exams Page 10 Only NYS Regents

11 Base your answers to questions 57 and 58 on the information below. Underground iron pipes in contact with moist soil are likely to corrode. This corrosion can be prevented by applying the principles of electrochemistry. Connecting an iron pipe to a magnesium block with a wire creates an electrochemical cell. The magnesium block acts as the anode and the iron pipe acts as the cathode. A diagram of this system is shown below. 57. Explain, in terms of reactivity, why magnesium is preferred over zinc to protect underground iron pipes. Your response must include both magnesium and zinc. 58. State the direction of the flow of electrons between the electrodes in this cell. Base your answers to questions 59 and 60 on the following information. A flashlight can be powered by a rechargeable nickel-cadmium battery. In the battery, the anode is Cd(s) and the cathode is NiO2(s). The unbalanced equation below represents the reaction that occurs as the battery produces electricity When a nickel-cadmium battery is recharged, the reverse reaction occurs. Cd(s) + NiO2(s) + H2O( ) Cd(OH)2(s) + Ni(OH)2(s) 59. Explain why Cd would be above Ni if placed on Table J. '08 to '12 Regents Exams Page 11 Only NYS Regents

12 60. Determine the change in oxidation number for the element that makes up the anode in the reaction that produces electricity '08 to '12 Regents Exams Page 12 Only NYS Regents

13 '08 to '12 Regents Exams Page 13 Only NYS Regents

Redox and Voltaic Cells

Name: Redox and Voltaic Cells Period: 1. Which half-reaction equation represents the reduction of an iron(ii) ion? 1) Fe 2+ Fe 3+ + e 2) Fe 2+ + 2e Fe 1) 1 to +2 2) 1 to 2 3) Fe 3+ + e Fe 2+ 4) Fe Fe 2+