Redox and Electrochemistry

Transcription

1 Name: Thursday, May 08, 2008 Redox and Electrochemistry 1. A diagram of a chemical cell and an equation are shown below. When the switch is closed, electrons will flow from 1. the Pb(s) to the Cu(s) the Pb (aq) to the Pb(s) 2. the Cu(s) to the Pb(s) the Cu (aq) to the Cu(s) 2. Which statement is true about oxidation and reduction in an electrochemical cell? 1. Both occur at the anode. 3. Oxidation occurs at the anode and reduction occurs at the cathode. 2. Both occur at the cathode. 4. Oxidation occurs at the cathode and reduction occurs at the anode. 3. Which process requires an external power source? 1. neutralization 3. fermentation 2. synthesis 4. electrolysis

2 4. An electrolytic cell is different from a voltaic cell because in an electrolytic cell 1. a redox reaction occurs 3. an electric current is produced 2. a spontaneous reaction occurs 4. an electric current causes a chemical reaction 5. What is the oxidation number of nitrogen in NO(g)? Answer: 6. Which half-reaction correctly represents a reduction reaction? Sn + 2e Sn Na + e Na Li + e Li 4. Br + 2e 2Br What is the oxidation number of chlorine in HClO? Which type of reaction is occurring when a metal undergoes corrosion? 1. oxidation-reduction 3. polymerization 2. neutralization 4. saponification

3 9. Which statement best describes the reaction represented by the equation below? 2NaCl + 2H O + electricity Cl + H + 2NaOH The reaction occurs in a voltaic cell and releases 3. The reaction occurs in an electrolytic cell and releases energy. energy. 2. The reaction occurs in a voltaic cell and absorbs 4. The reaction occurs in an electrolytic cell and absorbs energy. energy Which changes occur when Pt is reduced? The Pt gains electrons and its oxidation number 3. The Pt loses electrons and its oxidation number increases. increases The Pt gains electrons and its oxidation number 4. The Pt loses electrons and its oxidation number decreases. decreases. 11. Which quantities are conserved in all oxidation-reduction reactions? 1. charge, only 3. both charge and mass 2. mass, only 4. neither charge nor mass In the reaction: Pb + 2Ag Pb + 2Ag, the Ag is 1. reduced, and the oxidation number changes from oxidized, and the oxidation number changes from 0 to to reduced, and the oxidation number changes from oxidized, and the oxidation number changes from +1 to 0 to 0

4 13. In the redox reaction: Fe(s) + CuSO (aq) FeSO (aq) + Cu(s), there is a conservation of mass, only 3. both mass and charge 2. charge, only 4. neither mass nor charge 14. Which statement correctly describes a redox reaction? 1. The oxidation half-reaction and the reduction 3. The oxidation half-reaction occurs after the reduction half-reaction occur simultaneously. half-reaction. 2. The oxidation half-reaction occurs before the 4. The oxidation half-reaction occurs spontaneously but reduction half-reaction. the reduction half-reaction does not Given the reaction: Fe(s) + Sn (aq) Fe (aq) + Sn (aq) The oxidizing agent is Fe(s) 3. Fe (aq) Sn (aq) 4. Sn (aq) 16. What is the oxidation number of carbon in NaHCO? Which equation shows conservation of both mass and charge? Cl + Br Cl + Br 3. Zn + Cr Zn + Cr 2. Cu + 2 Ag Cu + Ag 4. Ni + Pb Ni + Pb

5 18. An electrochemical cell that generates electricity contains half-cells that produce 1. oxidation half-reactions, only 3. spontaneous redox reactions 2. reduction half-reactions, only 4. nonspontaneous redox reactions 19. Which half-reaction correctly represents reduction? Fe + 2e Fe Fe + e Fe Fe + 2e Fe Fe + e Fe 20. A discharging lead-acid battery is best described as 1. chemical cells that use an electric current 3. electrolytic cells that use an electric current 2. chemical cells that produce an electric current 4. electrolytic cells that produce an electric current 21. A voltaic cell differs from an electrolytic cell in that a chemical cell uses 1. half-reactions 3. an applied electric current 2. a solution of ions 4. a redox reaction to produce electricity 22. Which is a redox reaction? H + Cl HCl 3. Fe + 2HCl FeCl + H NaOH + HCl NaCl + H O 4. MgO + H SO MgSO + H O

6 Which change occurs when an Sn ion is oxidized? 1. Two electrons are lost. 3. Two protons are lost. 2. Two electrons are gained. 4. Two protons are gained. 24. Given the balanced ionic equation representing a reaction: Al (aq) + 3Mg(s) 3Mg (aq) + 2Al(s) In this reaction, electrons are transferred from Al to Mg 3. Mg to Al Al to Mg 4. Mg to Al 25. Which type of reaction occurs when nonmetal atoms become negative nonmetal ions? 1. oxidation 3. substitution 2. reduction 4. condensation

7 26. Figure 1 Which type of cell does the diagram represent? 1. electrolytic, with the anode at A 3. voltaic, with the anode at A 2. electrolytic, with the cathode at A 4. voltaic, with the cathode at A 27. A student collects the materials and equipment below to construct a voltaic cell. two 250-mL beakers wire and a switch one strip of magnesium one strip of copper 125 ml of 0.20 M Mg(NO 3) 2(aq) 125 ml of 0.20 M Cu(NO 3) 2(aq) Which additional item is required for the construction of the voltaic cell? 1. an anode 3. a cathode 2. a battery 4. a salt bridge

8 28. Figure 2 The diagram slows the electrolysis of fused KCl. What occurs when the switch is closed? 1. Positive ions migrate toward the anode, where they 3. Positive ions migrate toward the cathode, where they lose electrons. lose electrons. 2. Positive ions migrate toward the anode, where they 4. Positive ions migrate toward the cathode, where they gain electrons. gain electrons. 29. Which particles are gained and lost during a redox reaction? 1. electrons 3. neutrons 2. protons 4. positrons 30. Given the reaction: 2Na(s) + 2H2O(l) 2NaOH(aq) + H 2(g ) Which substance undergoes oxidation? 1. Na 3. H 2 2. NaOH 4. H O 2

9 31. Which balanced equation represents an oxidation-reduction reaction? 1. BaCl + Na SO BaSO + 2NaCl C + H O CO + H CaCO CaO + CO Mg(OH) + 2HNO Mg(NO ) + 2H O When the equation Pb + Au Pb + Au is correctly balanced using the smallest whole-number coefficients, the coefficient of Pb will be 33. Which half-cell reaction correctly represents reduction? Cu (aq) + e Cu(s) Cu(s) Cu (aq) + 2e H(g) + e H (aq) H (g) 2H (aq) + 2e 2

10 34. Figure 3 Write the balanced half-reaction for the reduction that occurs in this electrolytic cell Cl 2 + 2e 2Cl Cl2 2Cl + 2e 3. 2Na + + 2e - 2Na Na 2Na + 2e 35. Given the reaction: 2Li(s) + Cl 2(g) 2LiCl(s) As the reaction takes place, the Cl 2(g) will 1. gain electrons 3. gain protons 2. lose electrons 4. lose protons 36. The purpose of a salt bridge in a voltaic cell is to 1. allow for the flow of molecules between the solutions 3. prevent the flow of molecules between the solutions 2. allow for the flow of ions between the solutions 4. prevent the flow of ions between the solutions

11 37. Which statement is true for any electrochemical cell? 1. Oxidation occurs at the anode, only. 3. Oxidation occurs at both the anode and the cathode. 2. Reduction occurs at the anode, only. 4. Reduction occurs at both the anode and the cathode. 38. In which compound does sulfur have an oxidation number of -2? 1. SO 2 3. Na2S 2. SO 3 4. Na2SO4 39. Figure 4 The diagram represents a chemical cell at 298 K and 1 atmosphere. Which species represents the cathode? 1. Zn 3. Cu Zn 4. Cu

12 40. Given the reaction: Which species undergoes reduction? 1. Al Al 2. Fe Fe 41. What is the purpose of the salt bridge in a voltaic cell? 1. It blocks the flow of electrons. 3. It is a path for the flow of electrons. 2. It blocks the flow of positive and negative ions. 4. It is a path for the flow of positive and negative ions Given the balanced equation: 3Fe (aq) + Al(s) 3Fe (aq) + Al (aq) What is the total number of moles of electrons lost by 2 moles of Al(s)? 1. 1 mole 3. 3 moles 2. 6 moles 4. 9 moles Given the reaction: Ca(s) + Cu (aq) Ca (aq) + Cu(s) What is the correct reduction half-reaction? Cu (aq) + 2e Cu(s) 3. Cu(s) + 2e Cu (aq) Cu (aq) Cu(s) + 2e Cu(s) Cu (aq) + 2e 44. Given the redox reaction: Ni + Sn Ni + Sn Which species has been oxidized? Ni 3. Ni Sn 4. Sn

13 45. Figure 5 The diagram shows an electrolytic cell in which the electrodes are tin and copper. When the switch is closed, what will happen to the two electrodes? 1. B will dissolve and A will become coated with tin. 3. B will dissolve and A will become coated with copper. 2. A will dissolve and B will become coated with tin. 4. A will dissolve and B will become coated with copper. 46. Figure 6 The diagram represents the electroplating of a metal fork with Ag(s). Which part of the electroplating is represented by the fork? 1. the anode, which is the negative electrode 3. the anode, which is the positive electrode 2. the cathode, which is the negative electrode 4. the cathode, which is the positive electrode

14 Given the redox reaction: Fe (aq) + Zn(s) Zn (aq) + Fe(s) Which species acts as a reducing agent? 1. Fe(s) 3. Zn(s) Fe (aq) 4. Zn (aq) 48. Given the balanced ionic equation: Zn(s) + Cu (aq) Zn (aq) + Cu(s) Which equation represents the oxidation half-reaction? Zn(s) + 2e Zn (aq) 3. Cu (aq) Cu(s) + 2e Zn(s) Zn (aq) + 2e Cu (aq) + 2e Cu(s) 49. Which energy conversion occurs during the operation of a voltaic cell? 1. Chemical energy is spontaneously converted to 3. Electrical energy is spontaneously converted to electrical energy. chemical energy. 2. Chemical energy is converted to electrical energy only 4. Electrical energy is converted to chemical energy only when an external power source is provided. when an external power source is provided. 50. In which substance does chlorine have an oxidation number of +1? 1. Cl 3. HClO 2 2. HCl 4. HClO 2

15 Answer Key for Redox and Electrochemistry

16 Redox and Electrochemistry