Chemistry -Test Electrochemistry

Chemistry 12

Unit 5 Pre−Test

Unit 5 Electrochemistry

Electrochemistry

PART A: Multiple Choice Questions For each of the following, choose the alternative that BEST answers answers the question or completes the statement.

1. Consider the the following following skeletal skeletal redox reaction in acidic solution: Mn

3+

2+

Mn + MnO2



Which of the following is the balanced oxidation half-reaction? 3+ + A. 2H2O + Mn  MnO2 + 4H + e – 3+ – B. O2 + Mn  MnO2 + 3e 3+ 2+ C. e – + Mn  Mn 3+ 2+ – D. Mn  Mn + e 2. Consider the the following following balanced balanced redox equation in acidic acidic solution: –

5H2O + 2CoCl2 + OCl

+

–

2Co(OH)3 + 5Cl + 4H



–

Which of the following describes the amounts and locations of OH and H2O if the equation is balanced in basic solution? – A. 1 H2O on the left and 4OH on the right – B. 5 H2O on the left and 4OH on the left – C. 1 H2O on the left and 4OH on the left – D. 1 H2O on the left and no OH . 3. An oxidizing agent A. is oxidized. B. is reduced. C. causes another reactant to be reduced. D. loses electrons. 4. Consider the following equation: 2 –

Co + SO4 + 4H

+

2+

Co + H2SO3 + H2O



Which statement is correct? A. The hydrogen hydrogen is reduced and the oxygen is oxidized. B. The hydrogen hydrogen is reduced and and the cobalt is oxidized. C. The cobalt cobalt is oxidized and the sulphur sulphur is is reduced. D. The sulphur sulphur is oxidized and the cobalt is reduced. reduced. 5. Which of the following contains molybdenum molybdenum with its highest highest oxidation number? number? A. Mo6Cl12 B. MoCl5 C. Mo2S3 2 – D. MoO4 ver. 06/2012

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6. What is the oxidation number of carbon in the ethanoate ion C2H3O2 ? A. +1 B. +½ C. 0 D. –1 7. Which of the following changes involve sulphur atoms losing electrons? A. H2SO4  H2S2O7 B. SO2  S 2 – C. S2Cl2  S2 2 2 D. S2O3 –  SO4 – 8. Which of the following skeletal half-reactions are reductions?

A. B. C. D.

I

Mn(OH)2  MnO2

II

H2O  H2

III

H2O2  OH−

I and II only II and III only I, II and III only I only

9. Which of the following is the strongest oxidizing agent? + A. Ag B. Cl – C. Br2 D. Na 10. What is the result of adding Pb(s) to CuSO4(aq)? A. A reaction occurs but the electrical conductivity of the solution remains the same. B. No reaction occurs. C. The electrical conductivity of the solution increases. D. The electrical conductivity of the solution decreases. 3+

–

3+

–

11. If Fe (aq) and Cl (aq) are mixed, FeCl3(aq) results. However, if Fe (aq) and I (aq) are mixed, FeI3(aq) does not result. Which of the following best describes why? 3+ A. Fe is too strong a reducing agent. 3+ B. Fe forms an acidic solution. C. I – is oxidized in the solution. D. FeI3 is soluble.

Electrochemistry Pre-Test.docx

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12. A redox titration is carried out by adding purple KMnO4 solution from a burette to a solution of H2O2 in a flask, under acidic conditions. Which of the following would correc tly describe the observed colour and the product formed in the flask before the equivalence point is reached?

A. B. C. D.

Observed Colour becomes colourless remains purple remains purple becomes colourless

Product Formed O2 H2 O2 H2

13. Consider the following redox reaction: 2 –

–

2I2 + S2O3 + 3H2O  4I + 2H2SO3 + 2H

+

A 10.0 mL sample of an I2 solution is titrated with 13.2 mL of 0.0374 M Na2S2O3. What is the [I2 ] of the sample? A. 0. 0987 M B. 0. 0494 M C. 0. 0426 M D. 0. 0247 M 14. The titration of a 25.0 mL SnCl2 sample, in acidic solution, requires 14.4 mL of 0.030 M K2Cr2O7. The balanced equation for the reaction is shown below: 2

+

2+

Cr2O7 – + 14H + 3Sn

4+

3+

3Sn + 2Cr + 7H2O



What is the number of moles of SnCl2 in the original sample? –4 A. 4.3 x 10 mol –4 B. 1.4 x 10 mol –2 C. 5.2 x 10 mol –3 D. 1.3 x 10 mol


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Chemistry 12


Use the following electrochemical cell diagram to answer questions 15 to 17.

15. What is the overall cell reaction? 2+ + A. Zn + 2H2O  Zn + H2O2 + 2H B. Zn + H2O2 + 2H+  Zn2+ + 2H2O + 2+ – C. Zn + H2O2 + 2H + 4e  Zn + 2H2O 2+ D. Zn + H2O2  Zn + H2O + ½O2 16. Which of the following is correct as the cell operates? +

A. B. C. D.

Direction of K Ion Migration toward the Zn toward the Pt toward the Zn toward the Pt

Mass of the Cathode increases remains the same remains the same increases

17. What is the cell voltage at equilibrium? A. +2.54V B. –2.54V C. 0.00V D. +1.02V 18. Consider the following reaction: 2+

+

Ni + 2Ag  2Ag + Ni Which of the following is true? E° Reaction A. +1.06 V spontaneous B. non-spontaneous –1.06 V C. non-spontaneous –0.54 V D. +0.54 V spontaneous


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Chemistry 12


Use the following diagram to answer questions 19 to 21.

19. Which of the following represents the anode half-cell reaction? + A. Ag + e –  Ag + – B. Ag  Ag + e C. 2Cl –  Cl2 + 2e – – – D. Cl2 + 2e  2Cl 20. What changes in mass occur to the anode and cathode?

A. B. C. D.

Anode Mass increases decreases decreases increases

Cathode Mass no change increases no change decreases

21. What is the voltage for this cell under standard conditions? A. +2.16 V B. –0.24 V C. –0.56 V D. +0.56 V


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Chemistry 12



22. What is the cathode reaction for this cell? + – A. H2O  ½O2 + 2H + 2e B. Na+ + e –  Na – – C. Br2 + 2e  2Br – – D. 2Br  Br2 + 2e 23. Which of the following best describes the movement of potassium ions and electrons as the cell operates? +

A. B. C. D.

K Ion Movement towards the Pt towards the Cu towards the Cu towards the Pt

Electron Movement towards the Pt towards the Pt towards the Cu towards the Cu

24. What is the standard cell voltage? A. +0.62V B. –0.75V C. +1.43V D. +0.75V


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Chemistry 12



25. What is the half-cell reaction at the anode? 2+ – A. Pd  Pd + 2e 2+ B. Ni  Ni + 2e – 2+ – C. Pd + 2e  Pd 2+ D. Ni + 2e –  Ni 26. What best describes the flow of electrons? A. from Pd to Ni B. from Ni to Pd C. into the solution around the Ni electrode D. from cathode to anode 27. What is the voltage for the oxidation half-reaction of Pd? A. +1. 14 V B. –0. 62 V C. +0. 62 V D. +0. 88 V


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Chemistry 12


Use the following half reactions to answer questions 28 and 29. –

1

+

−

2H2SO3 + 2H + 4e

2−

S2O3 + 3H2O



2+

2

SnCl62− + 2e−  Sn + 6Cl−

3

½ Hg22+ + e−  Hg(l)

4

+

Sb2O5 + 6H + 4e

−

+

2Sb(OH)2 + H2O



2

28. A redox reaction occurs when Sb2O5 is mixed with S2O3 – , but does not when Sb2O5 is mixed with Hg. A solution of SnCl62 – has no effect on S2O32 – . Which of the following describes the order of the halfreaction reduction potentials from highest to lowest? A. 3 > 4 > 1 > 2 B. 2 > 1 > 4 > 3 C. 2 > 4 > 1 > 3 D. 3 > 1 > 4 > 2 29. The initial voltage of a standard electrochemical cell based on the half-reactions 3 and 4 above, is 2+ 0.22V. If Hg2 is reduced, what is the reduction potential for half-reaction 4? A. +1.02V B. +0.63V C. +0.58V D. –0.58V


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30. In the above cell, which of the following best describes the movement of the electrons through the wire? A. They move from right to left towards the anode. B. They move from left to right towards the anode. C. They move from left to right towards the cathode. D. They move from right to left towards the cathode. 31. Which of the following best describes what happens to the mass of the anode and the mass of the cathode as the cell operates? Anode Mass Cathode Mass A. stays constant stays constant B. stays constant decreases C. decreases stays constant D. decreases increases 32. What is the standard voltage (E°) for the cell? A. +1.68 V B. +0.43 V C. +0.77 V D. +1.34 V 33. Which of the following would prevent the corrosion of an iron nail? A. Store the nail wrapped in cobalt wire in a beaker of distilled water. B. Store the nail in a beaker of distilled water. C. Store the nail in dry air. D. Store the nail in Cl2(g). 34. Which of the following occurs when a piece of iron is cathodically protected with Mg? 2+ – A. Fe + 2e  Fe 2+ B. Fe  Fe + 2e – 2+ – C. Mg + 2e  Mg 2+ D. Mg  Mg + 2e – Electrochemistry Pre-Test.docx

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Chemistry 12


35. This diagram represents an electrolytic cell:

Which of the following correctly describes t he labelled parts X and Y of the cell? X Y A. anode voltmeter B. anode power supply C. cathode voltmeter D. cathode power supply 36. Consider the electrolysis of molten MgCl2 using copper electrodes. Which of the following halfreactions will occur at the cathode? – 2+ A. Mg + 2e  Mg – – B. Cl2 + 2e  2Cl 2+ C. Mg  Mg + 2e – 2+ – D. Cu + 2e  Cu –

37. Which of the following is the anode half cell reaction for the electrolysis of molten KBr ? + A. K + e –  K + – B. K  K + e + C. H2O  2e – + 2H + ½O2 – – D. 2Br  Br2 + 2e


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Chemistry 12


Use the following diagram to answer questions 38 and 40.

38. What products would form at the anode and cathode as this cell operates? Anode Cathode 2+ A. Cu Ni B. I2 Ni C. Ni I2 D. O2 H2 39. In the above cell, if 1.0 M NiI2 is replaced with molten NiI 2 , what products would form at the electrodes? Anode Cathode A. Ni I2 B. I2 Ni 2+ C. Cu Ni D. O2 H2 40. Consider the following diagram:

Why would this cell fail to electroplate the Fe nail with copper? A. The porous barrier prevents reaction. B. The Fe nail is the cathode. C. The Fe nail is the anode. D. The Pt is inert.

END OF EXAMINATION


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Chemistry 12


Answers to Multiple Choice 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

A C B C D C D B C A


11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

C A A D D D C B B C

21. 22. 23. 24. 25. 26. 27. 28. 29. 30.

D C A D B B B A C D

31. 32. 33. 34. 35. 36. 37. 38. 39. 40.

A D C D D A D B B C

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Chemistry -Test Electrochemistry

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