A. Oxidation involves loss of electrons and a decrease in oxidation state. B. Oxidation involves gain of electrons and an increase in oxidation state.

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1 1. Which statement is correct? A. Oxidation involves loss of electrons and a decrease in oxidation state. B. Oxidation involves gain of electrons and an increase in oxidation state. C. Reduction involves loss of electrons and an increase in oxidation state. D. Reduction involves gain of electrons and a decrease in oxidation state. 2. What occurs during the operation of a voltaic cell based on the following reaction? Ni(s) + Pb 2+ (aq) Ni 2+ (aq) + Pb(s) External circuit Ion movement in solution A. electrons move from Ni to Pb Pb 2+ (aq) move away from Pb(s) B. electrons move from Ni to Pb Pb 2+ (aq) move toward Pb(s) C. electrons move from Pb to Ni Ni 2+ (aq) move away from Ni(s) D. electrons move from Pb to Ni Ni 2+ (aq) move toward Ni(s) 3. Which is the strongest reducing agent according to the spontaneous reactions below? 2Cr(s) + 3Fe 2+ (aq) 2Cr 3+ (aq) + 3Fe(s) Fe(s) + Pb 2+ (aq) Fe 2+ (aq) + Pb(s) A. Cr(s) B. Cr 3+ (aq) C. Pb 2+ (aq) D. Pb(s) 4. Aqueous solutions of AgNO 3, Cu(NO 3 ) 2 and Cr(NO 3 ) 3 are electrolyzed using the same quantity of electricity. How do the number of moles of metal formed compare? A. Ag = Cu = Cr B. Ag > Cu > Cr C. Ag < Cu < Cr D. Cu > Ag > Cr 5. The oxidation number of chromium is the same in all the following compounds except A. Cr(OH) 3 B. Cr 2 O 3 C. Cr 2 (SO 4 ) 3 D. CrO 3 6. Magnesium is a more reactive metal than copper. Which is the strongest oxidizing agent? A. Mg B. Mg 2+ C. Cu D. Cu Which processes occur during the electrolysis of molten sodium chloride? I. Sodium and chloride ions move through the electrolyte. II. III. Electrons move through the external circuit. Oxidation takes place at the positive electrode (anode). A. I and II only B. I and III only C. II and III only D. I, II and III 8. In which reaction does chromium undergo a change in oxidation number? 1

2 A. Cr 2 O 3 + 3H 2 SO 4 Cr 2 (SO 4 ) 3 + 3H 2 O B. Cr 2 (SO 4 ) 3 + 6NaOH 2Cr(OH) 3 + 3Na 2 SO 4 C. K 2 Cr 2 O 7 + 4H 2 SO 4 + 6HCl Cr 2 (SO 4 ) 3 + K 2 SO 4 + 7H 2 O + 3Cl 2 D. 2K 2 CrO 4 + H 2 SO 4 K 2 Cr 2 O 7 + K 2 SO 4 + H 2 O 9. When the following equation is balanced, what is the coefficient for Ce 4+? _SO _H 2 O + _Ce 4+ _SO _H + + _Ce 3+ A. 1 B. 2 C. 3 D The standard electrode potentials for two half-cells involving iron are given below. Fe 2+ (aq) + 2e Fe(s) Fe 3+ (aq) + e Fe 2+ (aq) E ο = 0.44 V E ο = V What is the equation and the cell potential for the spontaneous reaction that occurs when the two half-cells are connected? A. 3Fe 2+ (aq) Fe(s) + 2Fe 3+ (aq) E ο = V B. Fe 2+ (aq) + Fe 3+ (aq) 2Fe(s) E ο = V C. Fe(s) + 2Fe 3+ (aq) 3Fe 2+ (aq) E ο = V D. Fe(s) + 2Fe 3+ (aq) 3Fe 2+ (aq) E ο = V 11. Metallic tin can be produced by the electrolysis of a molten salt containing Sn 2+ ions. Which change(s) would double the amount of tin produced? I. Doubling the current passed during electrolysis II. III. Doubling the time used for electrolysis Using Sn 4+ ions instead of Sn 2+ ions A. I only B. II only C. I and II only D. I, II and III 12. What happens to the Cr 3+ (aq) ion when it is converted to CrO 2 4 (aq)? A. Its oxidation number decreases and it undergoes reduction. B. Its oxidation number decreases and it undergoes oxidation. C. Its oxidation number increases and it undergoes reduction. D. Its oxidation number increases and it undergoes oxidation. 13. The following reactions are spontaneous as written. Fe(s) + Cd 2+ (aq) Fe 2+ (aq) + Cd(s) 2

3 Cd(s) + Sn 2+ (aq) Cd 2+ (aq) + Sn(s) Sn(s) + Pb 2+ (aq) Sn 2+ (aq) + Pb(s) Which of the following pairs will react spontaneously? I. Sn(s) + Fe 2+ (aq) II. Cd(s) + Pb 2+ (aq) III. Fe(s) + Pb 2+ (aq) A. I only B. II only C. III only D. II and III only 14. What species are produced at the positive and negative electrodes during the electrolysis of molten sodium chloride? Positive electrode Negative electrode A. Na + (l) Cl 2 (g) B. Cl (l) Na + (l) C. Na(l) Cl 2 (g) D. Cl 2 (g) Na(l) 15. What is the coefficient for H + when the equation below is balanced? Pb(s) + NO 3 (aq) + H + (aq) Pb 2+ (aq) + NO(g) + H 2 O(l) A. 2 B. 4 C. 6 D Which of the following factors affect the amount of product formed during electrolysis? I. The current used II. The duration of electrolysis III. The charge on the ion A. I and II only B. I and III only C. II and III only D. I, II and III 17. Consider the following reaction. H 2 SO 3 (aq) + Sn 4+ (aq) + H 2 O(l) Sn 2+ (aq) + HSO 4 (aq) + 3H + (aq) Which statement is correct? A. H 2 SO 3 is the reducing agent because it undergoes reduction. B. H 2 SO 3 is the reducing agent because it undergoes oxidation. C. Sn 4+ is the oxidizing agent because it undergoes oxidation. D. Sn 4+ is the reducing agent because it undergoes oxidation. 18. In which change does oxidation occur? A. CH 3 CHO CH 3 CH 2 OH B. CrO 4 2 Cr 2 O 7 2 C. SO 4 2 SO 3 2 D. NO 2 NO What happens at the positive electrode in a voltaic cell and in an electrolytic cell? 3

4 Voltaic cell Electrolytic cell A. Oxidation Reduction B. Reduction Oxidation C. Oxidation Oxidation D. Reduction Reduction 20. The cyanide ion, CN, can form two complex ions with iron ions. The formulas of these ions are [Fe(CN) 6 ] 4 and [Fe(CN) 6 ] 3. What is the oxidation number of iron in the two complex ions? [Fe(CN) 6 ] 4 [Fe(CN) 6 ] 3 A. 4 3 B C D Consider the following reactions. Cu 2+ (aq) + 2e Cu(s) E ο = V Mg 2+ (aq) + 2e Mg(s) E ο = 2.36 V Zn 2+ (aq) + 2e Zn(s) E ο = 0.76 V Which statement is correct? A. Cu 2+ (aq) will oxidize both Mg(s) and Zn(s). B. Zn(s) will reduce both Cu 2+ (aq) and Mg 2+ (aq). C. Mg 2+ (aq) will oxidize both Cu(s) and Zn(s). D. Cu(s) will reduce both Mg 2+ (aq) and Zn 2+ (aq). 22. Consider the standard electrode potentials of the following reactions. Cr 3+ (aq) + 3e Cr(s) Cd 2+ (aq) + 2e Cd(s) 0.75 V 0.40 V What is the value of the cell potential (in V) for the following reaction? 2Cr(s) + 3Cd 2+ (aq) 2Cr 3+ (aq) + 3Cd(s) A B C D Aqueous solutions containing different concentrations of NaCl were electrolysed using platinum electrodes. What is the major product at the positive electrode in each case? mol dm 3 NaCl(aq) 1.0 mol dm 3 NaCl(aq) A. H 2 Na B. H 2 H 2 4

5 C. O 2 Cl 2 D. Cl 2 O What are the oxidation numbers of the elements in sulfuric acid, H 2 SO 4? Hydrogen Sulfur Oxygen A B C D A voltaic cell is made from copper and zinc half-cells. The equation for the reaction occurring in the cell is Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s) Which statement is correct when the cell produces electricity? A. Electrons are lost from zinc atoms. B. The mass of the copper electrode decreases. C. Electrons flow from the copper half-cell to the zinc half-cell. D. Negative ions flow through the salt bridge from the zinc half-cell to the copper half-cell. 26. What happens when molten sodium chloride is electrolysed in an electrolytic cell? A. Chlorine is produced at the positive electrode. B. Sodium ions lose electrons at the negative electrode. C. Electrons flow through the liquid from the negative electrode to the positive electrode. D. Oxidation occurs at the negative electrode and reduction at the positive electrode. 27. The unbalanced equation for the conversion of sulfur dioxide to sulfuric acid is given below. SO 2 + H 2 O H 2 SO 4 Which other species are used, and on which side of the equation, to balance it? A. H + and e on the left B. H + on the left and e on the right C. H + on the right and e on the left D. H + and e on the right 28. Which is a feature of the standard hydrogen electrode? A. hydrogen gas at Pa (1 atm) pressure B. 1.0 mol dm 3 sulfuric acid C. a temperature of 273 K D. a magnesium electrode 29. Which pair of factors both affect the amount (in mol) of chlorine produced in the electrolysis of aqueous 5

6 sodium chloride? A. current and temperature B. temperature and chloride ion concentration C. chloride ion concentration and length of time of electrolysis D. pressure and length of time of electrolysis 30. Which equations represent reactions that occur at room temperature? I. 2Br (aq) + Cl 2 (aq) 2Cl (aq) + Br 2 (aq) II. III. 2Br (aq) + I 2 (aq) 2I (aq) + Br 2 (aq) 2I (aq) + Cl 2 (aq) 2Cl (aq) + I 2 (aq) A. I and II only B. I and III only C. II and III only D. I, II and III 31. Which equation represents a redox reaction? A. KOH(aq) + HCl(aq) KCl(aq) + H 2 O(l) B. Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) C. CuO(s) + 2HCl(aq) CuCl 2 (aq) + H 2 O(l) D. ZnCO 3 (s) + 2HCl(aq) ZnCl 2 (aq) + CO 2 (g) + H 2 O(l) 32. The following information is given about reactions involving the metals X, Y and Z and solutions of their sulfates. X(s) + YSO 4 (aq) no reaction Z(s) + YSO 4 (aq) Y(s) + ZSO 4 (aq) When the metals are listed in decreasing order of reactivity (most reactive first), what is the correct order? A. Z Y X B. X Y Z C. Y X Z D. Y Z X 33. From the given standard electrode potentials which statement is correct? Ca 2+ (aq) + 2e Ca(s) E Ө = 2.87 V Ni 2+ (aq) + 2e Ni(s) E Ө = 0.23 V Fe 3+ (aq) + e Fe 2+ (aq) E Ө = V A. Ca 2+ (aq) can oxidize Ni(s) B. Ni 2+ (aq) can reduce Ca 2+ (aq) C. Fe 3+ (aq) can oxidize Ni(s) D. Fe 3+ (aq) can reduce Ca 2+ (aq) 34. Which statement is correct about the electrolysis of copper(ii) sulfate solution using graphite electrodes? A. A colourless gas is produced at the negative electrode. B. The electrolyte does not change colour. C. The negative electrode decreases in mass. 6

7 D. A colourless gas is produced at the positive electrode. 35. What are the oxidation numbers of the elements in the compound phosphoric acid, H 3 PO 4? Hydrogen Phosphorus Oxygen A B C D A voltaic cell is made from magnesium and iron half-cells. Magnesium is a more reactive metal than iron. Which statement is correct when the cell produces electricity? A. Electrons are lost from magnesium atoms. B. The concentration of Fe 2+ ions increases. C. Electrons flow from the iron half-cell to the magnesium half-cell. D. Negative ions flow through the salt bridge from the magnesium half-cell to the iron half-cell. 37. A metallic object is electroplated with copper using a solution of copper(ii) sulfate. Which statement is correct? A. The positive electrode increases in mass. B. The concentration of Cu 2+ ions in the solution decreases. C. Reduction occurs at the positive electrode. D. The reaction occurring at the negative electrode is Cu e Cu. 38. Two half-equations and their standard electrode potentials are shown in the table. Half-equation E Ө / V Pb 2+ (aq) + 2e Pb(s) 0.13 Ag + (aq) + e Ag(s) What is the cell potential, in V, for the reaction below? Pb(s) + 2Ag + (aq) Pb 2+ (aq) + 2Ag(s) A B C D Two electrolytic cells are connected in series so that the same current flows through both cells for the same length of time. 7

8 SnSO 4(aq) CuSO 4(aq) The amount of tin deposited is 0.01 mol. How much copper is deposited? A mol B mol C mol D mol 40. Which are examples of reduction? I. Fe 3+ becomes Fe 2+ II. Cl becomes Cl 2 III. CrO 3 becomes Cr 3+ A. I and II only B. I and III only C. II and III only D. I, II and III 41. Which statement is correct for the electrolysis of a molten salt? A. Positive ions move toward the positive electrode. B. A gas is produced at the negative electrode. C. Only electrons move in the electrolyte. D. Both positive and negative ions move toward electrodes. 42. Which statement about the following reaction is correct? 2Br (aq) + Cl 2 (aq) Br 2 (aq) + 2Cl (aq) A. Br (aq) is reduced and gains electrons. B. Cl 2 (aq) is reduced and loses electrons. C. Br (aq) is oxidized and loses electrons. D. Cl 2 (aq) is oxidized and gains electrons. 43. Which are used for the electroplating of a metal spoon with copper? I. an electrolyte containing aqueous copper(ii) ions II. III. a copper anode (positive electrode) a copper cathode (negative electrode) A. I and II only B. I and III only C. II and III only D. I, II and III 44. Consider these standard electrode potentials. Cu 2+ (aq) + e Cu + (aq) Cu + (aq) + e Cu(s) E Ө = V E Ө = V What is the standard cell potential when the two half-cells are connected? A V B V C V D V 45. Consider the following spontaneous reactions. 8

9 Fe(s) + Cu 2+ (aq) Fe 2+ (aq) + Cu(s) Cu(s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag(s) Zn(s) + Fe 2+ (aq) Zn 2+ (aq) + Fe(s) Which is the correct combination of strongest oxidizing agent and strongest reducing agent? Strongest oxidizing agent Strongest reducing agent A. Ag(s) Zn(s) B. Ag + (aq) Zn(s) C. Zn 2+ (aq) Ag(s) D. Zn(s) Ag + (aq) 46. In which change does nitrogen undergo oxidation? A. NO 2 N 2 O 4 B. NO 3 NO 2 C. N 2 O 5 NO 3 D. NH 3 N Which statement is correct? A. Spontaneous redox reactions produce electricity in an electrolytic cell. B. Electricity is used to carry out a non-spontaneous redox reaction in a voltaic cell. C. Oxidation takes place at the negative electrode in a voltaic cell and the positive electrode in an electrolytic cell. D. Oxidation takes place at the negative electrode in a voltaic cell and reduction takes place at the positive electrode in an electrolytic cell. 48. The compound [Co(NH 3 ) 5 Br]SO 4 is isomeric with the compound [Co(NH 3 ) 5 SO 4 ]Br. What is the oxidation state of cobalt in these compounds? [Co(NH 3 ) 5 Br]SO 4 [Co(NH 3 ) 5 SO 4 ]Br A B C D Consider the standard electrode potentials of the following reactions: Sn 4+ (aq) + 2e Sn 2+ (aq) Fe 3+ (aq) + e Fe 2+ (aq) V V What is the value of the cell potential (in volts) for the spontaneous reaction? A B C D In the electrolysis of acidified water, if 8.4 cm 3 of hydrogen gas is evolved, what volume of oxygen gas is evolved? 9

10 A. 4.2 cm 3 B. 8.4 cm 3 C cm 3 D cm Which factors affect the amount of metal formed during electrolysis? I. Charge on the metal ion II. Current III. Time A. I and II only B. I and III only C. II and III only D. I, II and III 52. What happens to vanadium during the reaction VO 2+ (aq) VO 3 (aq)? A. It undergoes oxidation and its oxidation number changes from +4 to +5. B. It undergoes oxidation and its oxidation number changes from +2 to +4. C. It undergoes reduction and its oxidation number changes from +2 to 1. D. It undergoes reduction and its oxidation number changes from +4 to What occurs during the electrolysis of a molten salt? A. Electricity is produced by a spontaneous redox reaction. B. Electricity is used to cause a non-spontaneous redox reaction to occur. C. Electrons flow through the molten salt. D. Electrons are removed from both ions of the molten salt. 54. Which statement is correct about an oxidizing agent in a chemical reaction? A. It reacts with oxygen. B. It reacts with H + ions. C. It loses electrons. D. It undergoes reduction. 55. Which formula represents an aldehyde? A. CH 3 CH 2 CHO B. CH 3 COCH 3 C. CH 3 CH 2 COOH D. CH 3 COOCH The standard electrode potentials for two half reactions are V 2+ (aq) + 2e V(s) Tl + (aq) + e Tl(s) 1.19 V 0.34 V What is the E Ө value (in volts) for the following reaction? V(s) + 2Tl + (aq) V 2+ (aq) + 2Tl(s) A B C D

11 57. Which changes lead to the production of more moles of metal during the electrolysis of a molten salt? I. using a metal ion with a higher charge II. III. increasing the current using a longer time A. I and II only B. I and III only C. II and III only D. I, II and III 58. What is the reducing agent in this reaction? Cu(s) + 2 NO 3 (aq) + 4H + (aq) Cu 2+ (aq) + 2NO 2 (g) + 2H 2 O(l) A. Cu(s) B. NO 3 (aq) C. Cu 2+ (aq) D. H + (aq) 59. A particular voltaic cell is made from magnesium and iron half-cells. The overall equation for the reaction occurring in the cell is Mg(s) + Fe 2+ (aq) Mg 2+ (aq) + Fe(s) Which statement is correct when the cell produces electricity? A. Magnesium atoms lose electrons. B. The mass of the iron electrode decreases. C. Electrons flow from the iron half-cell to the magnesium half-cell. D. Negative ions flow through the salt bridge from the magnesium half-cell to the iron half-cell. 60. What process occurs at the cathode in a voltaic cell and at the anode in an electrolytic cell? Cathode of voltaic cell Anode of Electrolytic cell A. Oxidation Reduction B. Oxidation Oxidation C. Reduction Oxidation D. Reduction Reduction 61. Consider the following reaction: H 2 SO 3 (aq) + Sn 4+ (aq) + H 2 O(l) Sn 2+ (aq) + HSO 4 (aq) + 3H + (aq) Which statement is correct? A. H 2 SO 3 is the reducing agent because it undergoes reduction. B. H 2 SO 3 is the reducing agent because it undergoes oxidation. C. Sn 4+ is the oxidizing agent because it undergoes oxidation. D. Sn 4+ is the reducing agent because it undergoes oxidation. 62. Which processes occur during the electrolysis of molten sodium chloride? 11

12 I. Sodium and chloride ions move through the electrolyte. II. Electrons move through the external circuit. III. Oxidation takes place at the anode. A. I and II only B. I and III only C. II and III only D. I, II and III 63. Which equation represents the reduction process occurring in the standard hydrogen electrode? A. H 2 (g) 2H + (aq) + 2e B. H + (aq) + OH (aq) H 2 O(l) C. 2H + (aq) + 2e H 2 (g) D. O 2 (g) + 4H + (aq) + 4e 2H 2 O(l) 64. Which statement is correct about the value of E ο? A. The more positive the value of E ο, the greater the driving force for reduction. B. The more negative the value of E ο, the greater the driving force for reduction. C. The more positive the value of E ο, the greater the rate of reaction. D. The more negative the value of E ο, the greater the rate of reaction. 65. Direction of electron flow A Zn(s) Salt bridge Cu(s) 2+ Zn (aq) 2+ Cu (aq) (a) The apparatus shown above may be used to carry out a redox reaction. State the function of the salt bridge. 12

13 Write a half-equation for the oxidation reaction. (iii) The above reactions are carried out under standard conditions. State what the standard conditions are for the cell. (iv) Using the Data Booklet, calculate the cell potential for the above cell. (v) State and explain what happens to the concentration of the copper(ii) ions when the cell is producing an electric current. (vi) State two observations that could be made if the zinc rod were placed in a solution of copper(ii) ions. (b) The standard electrode potentials for three electrode systems are given below. Ti 3+ (aq) + e Ti 2+ (aq) E ο = 0.37 V Fe 3+ (aq) + e Fe 2+ (aq) Ce 4+ (aq) + e Ce 3+ (aq) E ο = V E ο = V Using the data above, deduce which species is the best reducing agent, giving a reason in terms of electrons for your answer. 13

14 Write an equation, including state symbols, for the overall reaction with the greatest cell potential. (iii) State and explain the sign of G ο for the reaction in (b). (c) State the name of a solution that would produce only hydrogen and oxygen when electrolyzed using platinum electrodes. Draw a diagram of apparatus that would allow the gases produced in the reaction in (c) to be collected separately. Annotate your diagram to show the polarity of each electrode and the names and relative volumes of each gas. (3) (Total 20 marks) 14

15 66. + A X Y CuSO (aq) 4 Two copper strips X and Y are placed in an aqueous solution of copper(ii) sulfate and electrolyzed for a certain time. X was then dried and weighed. State and explain what would happen to the mass of X (3) State two ways in which the change in the mass of X could be increased..... (Total 5 marks) 67. Consider the following redox equation. 5Fe 2+ (aq) +MnO 4 (aq) +8H + (aq) 5Fe 3+ (aq) + Mn 2+ (aq) + 4H 2 O(l) Determine the oxidation numbers for Fe and Mn in the reactants and in the products. Based on your answer to, deduce which substance is oxidized. 15

16 (iii) The compounds CH 3 OH and CH 2 O contain carbon atoms with different oxidation numbers. Deduce the oxidation numbers and state the kind of chemical change needed to make CH 2 O from CH 3 OH. (3) (Total 6 marks) 68. A part of the reactivity series of metals, in order of decreasing reactivity, is shown below. magnesium zinc iron lead copper silver If a piece of copper metal were placed in separate solutions of silver nitrate and zinc nitrate determine which solution would undergo reaction. identify the type of chemical change taking place in the copper and write the half-equation for this change. (iii) state, giving a reason, what visible change would take place in the solutions. (Total 5 marks) 69. Solid sodium chloride does not conduct electricity but molten sodium chloride does. Explain this difference, and outline what happens in an electrolytic cell during the electrolysis of molten sodium chloride using carbon electrodes. 16

17 (4) State the products formed and give equations showing the reactions at each electrode. (4) (iii) State what practical use is made of this process. (Total 9 marks) 70. (a) Some standard electrode potentials are shown in Table 15 of the Data Booklet. State three conditions under which the hydrogen electrode is assigned a potential of zero. (3) Calculate the cell potential of a cell made by connecting standard copper and zinc electrodes. State the direction of electron flow in the external circuit when the cell produces current. Outline the changes occurring at the electrodes and in the solutions during the process. 17

18 (5) (b) Using information from Table 15, determine whether or not there is a spontaneous reaction between copper metal and a solution containing hydrogen ions. (c) Using information from Table 15, identify a substance that will oxidize bromide ions but not chloride ions. Explain your choice, and write an equation for the redox reaction you have chosen. (5) (Total 15 marks) 71. A current is passed through molten sodium chloride. Identify the substance formed at each electrode and write an equation to represent the formation of each substance. Determine the mole ratio in which the substances are formed. (Total 5 marks) 72. Electrolysis can be used to obtain chlorine from molten sodium chloride. Write an equation for the reaction occurring at each electrode and describe the two different ways in which electricity is conducted when the cell is in operation. (Total 4 marks) 73. (a) In one experiment involving the electrolysis of molten sodium chloride, 0.1 mol of chlorine was formed. Deduce, giving a reason, the amount of sodium formed at the same time. 18

19 (b) In another experiment involving the electrolysis of molten sodium chloride, the time of the electrolysis was halved and the current increased from 1 amp to 5 amp, compared to the experiment in (a). Deduce the amount of chlorine formed, showing your working. (c) If dilute aqueous sodium chloride is electrolyzed, a different product is obtained at each electrode. Identify the product formed at each electrode and write an equation showing its formation. (4) (Total 8 marks) 74. Two reactions occurring in the manufacture of bromine from sea water are I II Cl 2 (g) + 2Br (aq) 2Cl (aq) + Br 2 (g) Br 2 (g) + SO 2 (g) + 2H 2 O(l) 2HBr(g) + H 2 SO 4 (g) Explain, by reference to electrons, why reaction I is referred to as a redox reaction. State and explain whether SO 2 is reduced or oxidized in reaction II by referring to the oxidation numbers of sulfur in this reaction. (3) (Total 5 marks) 75. Define the term standard electrode potential of an element. Table 15 of the Data Booklet contains E Ө values for two reactions involving O 2 (g). Identify the E Ө value of the reaction that could be used to oxidize bromide ions and explain your reasoning. Construct a balanced equation for the oxidation of bromide ions using this reaction and calculate the cell potential. (Total 8 marks) 76. In terms of electron transfer define: oxidation oxidizing agent (Total 2 marks) 77. Deduce the change in oxidation number of chromium in the below reaction. State with a reason whether the chromium has been oxidized or reduced. CrO H + + 6Fe 2+ 2Cr Fe H 2 O

20 ... (Total 2 marks) 78. (a) Define oxidizing agent in terms of electron transfer Deduce the change in oxidation number of chromium in the reaction below. State with a reason whether the chromium has been oxidized or reduced. Cr 2 O H + + 6Fe 2+ 2Cr H 2 O (Total 3 marks) 79. Iron in food, in the form of Fe 3+, reacts with ascorbic acid (vitamin C), C 6 H 8 O 6, to form dehydroascorbic acid, C 6 H 6 O 6. Write an ionic half-equation to show the conversion of ascorbic acid to dehydroascorbic acid in aqueous solution In the other ionic half-equation Fe 3+ is converted to Fe 2+. Deduce the overall equation for the reaction between C 6 H 8 O 6 and Fe (Total 2 marks) 80. Draw a diagram of apparatus that could be used to electrolyse molten potassium bromide. Label the diagram to show the polarity of each electrode and the product formed. (3) (iii) Describe the two different ways in which electricity is conducted in the apparatus. Write an equation to show the formation of the product at each electrode. (Total 7 marks) 20

21 81. Use information from Table 15 of the Data Booklet, where relevant, in answering this part. The diagram shows the apparatus used in an experiment involving half-cells. Nickel Voltmeter Lead Solution containing 2+ Ni (aq) Solution containing 2 Pb (aq) The reading on the voltmeter is 0.10 V. State two standard conditions that apply for this reading to be obtained. The voltmeter is replaced by a 2 volt power supply, so that non-spontaneous reactions occur. Deduce the half-equations for these reactions. (iii) Chlorine gas is formed when potassium manganate(vii) is added to concentrated hydrochloric acid. Calculate the cell potential for this reaction and deduce the equation for the reaction. (3) (iv) Explain why potassium dichromate(vi) does not react with concentrated hydrochloric acid. (Total 8 marks) 82. Iodide ions, I (aq), react with iodate ions, IO 3 (aq), in an acidic solution to form molecular iodine and water. Determine the oxidation number of iodine in each iodine-containing species in the reaction. Identify, with a reason, the species that undergoes: oxidation... reduction... (Total 4 marks) 83. (a) When a concentrated aqueous solution of sodium chloride is electrolyzed using inert electrodes, a different gas is produced at each electrode. Write equations for the oxidation and reduction half-reactions. Oxidation half-reaction:... 21

22 ... Reduction half-reaction: Explain why sodium is not formed during the electrolysis of aqueous NaCl solution (b) Deduce the products formed during the electrolysis of an aqueous solution of sodium fluoride. Write an equation for the reaction at the positive electrode (the anode) and give your reasoning (4) (Total 7 marks) 84. The following are standard electrode potentials. Half-equation E ο / V Zn 2+ (aq) + 2e Zn(s) 0.76 Cr 3+ (aq) + 3e Cr(s) 0.74 Fe 2+ (aq) + 2e Fe(s) 0.44 Sn 2+ (aq) + 2e Sn(s) 0.14 Cu 2+ (aq) + 2e Cu(s) Fe 3+ (aq) + e Fe 2+ (aq) (a) These values were obtained using a standard hydrogen electrode. Describe the materials and conditions used in the standard hydrogen electrode. (A suitably labelled diagram is acceptable.) 22

23 (5) (b) Define the term oxidizing agent in terms of electron transfer and identify the strongest oxidizing agent in the list above. (c) A cell was set up using zinc in zinc sulfate solution and copper in copper(ii) sulfate solution, both solutions being under standard conditions. Calculate the cell potential. Write an equation for the spontaneous cell reaction. (d) Both zinc and tin are used to coat iron to prevent it from rusting. Once the surface is scratched, oxygen and water containing dissolved ions come into contact with the iron and the coating metal. State and explain whether zinc or tin would be more effective in preventing iron from rusting under these conditions. Electroplating may be used to coat one metal with another metal. Identify the three factors affecting the amount of metal discharged during electroplating. 23

24 (3) (iii) Explain why electrolysis of aqueous zinc sulfate is not used for coating with zinc metal. (e) Another cell was set up as shown below. V Pt(s) Cr(s) 2+ Fe (aq), Fe (aq) Cr (aq) Y half-cell A half-cell B Identify the part of the cell labelled Y and outline its function. Write an equation for the initial reactions at each electrode and hence write an equation for the cell reaction. (4) (iii) Describe the direction of electron flow in the external circuit. 24

25 (iv) Calculate the cell potential. (Total 25 marks) 85. The following diagram shows a voltaic cell. voltmeter V salt bridge iron electrode silver electrode 2+ Fe (aq) + Ag (aq) (a) State an equation to represent the spontaneous reaction occurring in the cell. (b) Define the term standard electrode potential. (c) Use Table 15 from the Data Booklet to calculate the standard cell potential for the spontaneous reaction in (a). (d) Draw arrows on the above diagram to indicate the direction of electron flow. (Total 4 marks) 86. Tin(II) ions can be oxidized to tin(iv) ions by acidified potassium permanganate(vii) solution according to the following unbalanced equation. Sn 2+ + MnO 4 + H + Sn 4+ + Mn 2+ + H 2 O 25

26 (a) Identify the oxidizing agent and the reducing agent. Oxidizing agent... Reducing agent... (b) Balance the equation above. (Total 2 marks) 87. (a) Iodide ions, I (aq), react with iodate ions, IO 3 (aq), in an acidic solution to form molecular iodine and water. Determine the oxidation number of iodine in I and in IO Identify, with a reason, the species that undergoes: oxidation reduction (iii) Write an ionic equation for the reaction of I with IO 3 in an acidic solution (b) Use information from Table 15 of the Data Booklet to calculate the cell potential for the following reaction and state whether or not the reaction is spontaneous. Cu(s) + Cu 2+ (aq) 2Cu + (aq) (3) 26

27 (Total 8 marks) 88. A table of standard electrode potentials can be found in Table 14 of the Data Booklet. (a) Describe the materials and conditions used in the standard hydrogen electrode..... (5) (b) Define the term oxidizing agent in terms of electron transfer and identify the strongest oxidizing agent in Table 14 of the Data Booklet.... (c) A cell was set up using tin in tin(ii) sulfate solution and copper in copper(ii) sulfate solution, with both solutions under standard conditions. Calculate the cell potential Write an equation for the spontaneous cell reaction