SparkNotes: Review of Electrochemistry: Review Test

1. What is the oxidation state of H₂?

(A) 1

(B) 0

(C) -1

(D) 1/2

2. What is the oxidation state of gold in Au(CN)₄^-?

(A) 3

(B) -1

(C) 0

(D) 4

3. What is the change in oxidation state for carbon in the following reaction?

(A) -4

(B) +4

(C) -8

(D) +8

4. What is the oxidation state of Xe in XeOF₄?

(A) 2

(B) -2

(C) 6

(D) -6

5. In which of the following compounds does O have an oxidation state not equal to -2?

(A) H₂O

(B) HOF

(C) ClO₄^-

(D) H₂SO₄

6. Which of the following reactions is NOT a redox reaction?

(A) Na + Cl ---> NaCl

(B) H₂O₂ ---> HO₂^- + H⁺

(C) Ni²⁺ + Fe ---> Fe²⁺ + Ni

(D) NaOH + HCl ---> NaCl + H₂O

7. Which of the following terms best describes CH₄ in the following reaction?

(A) oxidized

(B) oxidizing agent

(C) hydrolyzed

(D) reduced

8. Which of the following are reduced in the following redox reaction?

(A) H⁺

(B) Fe²⁺

(C) H₂O

(D) Mn

9. What are the values of A-F that balance the following equation?

(A) A = 6, B = 4, C = 1, D = 4, E = 3, F = 2

(B) A = 2, B = 4, C = 1, D = 4, E = 1, F = 2

(C) A = 8, B = 4, C = 1, D = 4, E = 4, F = 2

(D) A = 8, B = 4, C = 1, D = 2, E = 4, F = 1

10. What are the values of A-G that balance the following equation?

(A) A = 3, B = 14, C = 36, D = 6, E = 9, F = 14, G = 18

(B) A = 3, B = 14, C = 18, D = 6, E = 9, F = 14, G = 18

(C) A = 3, B = 7, C = 18, D = 6, E = 9, F = 14, G = 9

(D) A = 3, B = 14, C = 6, D = 6, E = 3, F = 14, G = 18

11. What are the values of A-E that balance the following equation?

(A) A = 2, B = 4, C = 2, D = 2, E = 1

(B) A = 1, B = 4, C = 2, D = 2, E = 1

(C) A = 2, B = 4, C = 1, D = 2, E = 1

(D) A = 2, B = 4, C = 2, D = 1, E = 1

12. What are the values of A-E that balance the following equation?

(A) A = 2, B = 8, C = 4, D = 8, E = 3

(B) A = 2, B = 16, C = 2, D = 8, E = 3

(C) A = 2, B = 16, C = 4, D = 8, E = 1

(D) A = 2, B = 16, C = 4, D = 8, E = 3

13. What are the values of A-D that balance the following equation?

(A) A = 2, B = 2, C = 4, D = 2

(B) A = 3, B = 1, C = 4, D = 2

(C) A = 2, B = 1, C = 3, D = 2

(D) A = 2, B = 1, C = 3, D = 3

14. Give the line notation for a cell that reduces CuSO₄ to Cu and oxidizes Zn to Zn²⁺.

(A) Cu (s) | Cu²⁺ (aq) || Zn²⁺ (aq) | Zn (s)

(B) Zn (s) | Zn²⁺ (aq) || Cu²⁺ (aq) | Cu (s)

(C) Zn (s) | Zn²⁺ (aq), SO₄^2- (aq) || Cu²⁺ (aq), SO₄^2- (aq) | Cu (s)

(D) Cu (s) | Cu²⁺ (aq), SO₄^2- (aq) || Zn²⁺ (aq), SO₄^2- (aq) | Zn (s)

15. Give the line notation for the following redox reaction:

(A) Pt (s) | Fe²⁺ (aq), Fe³⁺ (aq) || MnO₄^- (aq), Mn²⁺ (aq), H⁺ (aq) | Pt (s)

(B) Pt (s) | Fe²⁺ (aq) || MnO₄^- (aq), H⁺ (aq) | Pt (s)

(C) Pt (s) | Fe²⁺ (aq), Fe³⁺ (aq), H⁺ (aq) || MnO₄^- (aq), Mn²⁺ (aq) | Pt (s)

(D) Pt (s) | MnO₄^- (aq), Mn²⁺ (aq), H⁺ (aq) || Fe²⁺ (aq), Fe³⁺ (aq) | Pt (s)

16. In the following galvanic cell, identify the direction of electron flow: Pt (s) | MnO₄^- (aq), Mn²⁺ (aq), H⁺ (aq) || Fe²⁺ (aq), Fe³⁺ (aq) | Pt (s)

(A) From anode to cathode: right half-cell to left half-cell

(B) From cathode to anode: right half-cell to left half-cell

(C) From cathode to anode: left half-cell to right half-cell

(D) From anode to cathode: left half-cell to right half-cell

17. What is the direction of ion flow through a porous disk in a galvanic cell?

(A) There is no ion flow through the disk whose purpose is to separate the two half-cells

(B) Negative ions flow from the oxidation half-cell to the reduction half-cell

(C) Positive ions flow from the anode half-cell to the cathode half-cell

(D) Negative ions flow from the oxidation half-cell to the reduction half-cell

18. What is the sign of DG for a galvanic cell?

(A) Positive

(B) Negative

(C) Either negative or positive

(D) Zero

19. What is the sign of E for a galvanic cell?

(A) Positive

(B) Negative

(C) Either positive or negative

(D) Zero

20. Which half-reaction takes place at the anode?

(A) The one with the greater reduction potential

(B) The one that transfers the most number of electrons

(C) The reduction

(D) The oxidation

21. Which of the following is an equation for DG?

(A) DG = DG^o - (RT/nF) ln Q

(B) DG = nFE

(C) DG = DG^o + RT ln Q

(D) DG = DH + TDS

22. What is the free energy of formation for water, given its E^o for decomposition into hydrogen and oxygen is -1.23 V?

(A) -475 kJ / mol

(B) -237 kJ / mol

(C) 237 kJ / mol

(D) 475 kJ / mol

23. Using your chemical intuition, which of the following species is the strongest oxidizing agent?

(A) F₂

(B) H₂

(C) Br₂

(D) Ca

24. What species must copper be oxidized to if the cell potential for one of its redox reactions is 1.0 V and the free energy of the reaction is -289.5 kJ / mol?

(A) Cu^-

(B) Cu²⁺

(C) Cu⁺

(D) Cu³⁺

25. What is a faraday?

(A) A unit of current

(B) A unit of energy

(C) A unit of charge

(D) A mole of electrons

26. What happens to the cell potential of a non-standard state reaction when the temperature increases?

(A) Decreases

(B) Increases

(C) Stays the same

(D) Not enough information to solve the problem

27. What happens to the potential of the following reaction when the concentration of Fe²⁺ is halved and the concentration of Mn²⁺ is doubled?

(A) Decreases

(B) Increases

(C) Stays the same

(D) Cannot be determined with the given information

28. Which of the following statements about concentration cells are true?

(A) The electrons flow from the cathode to the anode

(B) Their potentials are constant in time

(C) Useful voltages cannot be harnessed from such cells

(D) Reduced material can plate at the cathode

29. What is the potential of the following cell at 45^oC? Ag (s) | Ag⁺ (aq) || Ag⁺ (aq) [0.1 M] | Ag (s)

(A) 0.126 V

(B) 0.63 V

(C) 0.063 V

(D) -0.063 V

30. What is the direction of ion flow through the porous disk in a concentration cell?

(A) Negative ions flow from the anode compartment to the cathode compartment

(B) Positive ions flow from the oxidation half-cell to the reduction half-cell

(C) There is no ion flow in a concentration cell because it is not a real reaction

(D) Positive ions flow from the reduction half-cell to the oxidation half-cell

31. Why do most ships with iron hulls hang from those hulls a piece of magnesium?

(A) The magnesium has a greater oxidation potential than the iron and therefore acts as an anode, being dissolved into the ocean, while the ship's hull acts as a cathode and is this protected against corrosion.

(B) The magnesium has a greater reduction potential than the iron and therefore acts as an anode, being dissolved into the ocean, while the ship's hull acts as a cathode and is thus protected against corrosion.

(C) The magnesium has a greater reduction potential than the iron and therefore acts as a cathode, being dissolved into the ocean, while the ship's hull acts as an anode and is thus protected against corrosion.

(D) The magnesium has a greater oxidation potential than the iron and therefore acts as a cathode, being dissolved into the ocean, while the ship's hull acts as an anode and is thus protected against corrosion.

32. Even though redox reactions are reversible by applying an outside source emf, why aren't all batteries rechargeable?

(A) Redox reactions are not all reversible, and those used in batteries are good examples of non-reversible redox reactions.

(B) All batteries are, in fact, rechargeable but big business doesn't want you to know that.

(C) Because batteries are usually dry-cells, due to the lack of mixing of reagents it is unlikely that most of the reagents will come into contact with the electrodes and hence, can only react once and not be recharged.

(D) Redox reactions are not 100% efficient, that is to say that the yield on a redox reaction is generally not quantitative so multiple charges and discharges would make the battery's potential decrease dramatically due to the decrease in available reagents (Nernst Equation).

33. Which of the following redox reactions is primarily responsible for producing most of what you eat?

(A) CH₄ + O₂ ---> CH₃OH

(B) C₂H₆ + O₂ ---> C₂H₅OH

(C) CO₂ + H₂O ---> C₆H₁₂O₆

(D) CO₂ + CH₄ ---> C₂H₄O₂

34. What is the potential of the following reaction that has a DG of -264 kJ / mol? Na⁺ + Cl^- ---> NaCl

(A) 2.74 V

(B) 0

(C) 1.37 V

(D) -2.74 V

35. Aluminum, in the 18th century, was more valuable than gold. Explain why that was so, and why now the opposite is true.

(A) Al has a greater oxidation potential than Au, so Au was more abundant in its elemental form. After the discovery of electrolysis, it became a simple task to design a process to refine Al from its ore. Almost all the gold on earth, however, is in its elemental form so the discovery of electrolysis did not have such a profound effect on the price of Au as it did for Al.

(B) Al has a greater oxidation potential than Au, so Al was more abundant in its elemental form. After the discovery of electrolysis, it became a simple task to design a process to refine Au from its ore. Almost all the aluminum on earth, however, is in its elemental form so the discovery of electrolysis did not have such a profound effect on the price of Au as it did for Al.

(C) Al has a greater reduction potential than Au, so Au was more abundant in its elemental form. After the discovery of electrolysis, it became a simple task to design a process to refine Al from its ore. Almost all the gold on earth, however, is in its elemental form so the discovery of electrolysis did not have such a profound effect on the price of Au as it did for Al.

(D) Al has a greater reduction potential than Au, so Al was more abundant in its elemental form. After the discovery of electrolysis, it became a simple task to design a process to refine Au from its ore. Almost all the aluminum on earth, however, is in its elemental form so the discovery of electrolysis did not have such a profound effect on the price of Au as it did for Al.

36. At which electrode is H₂ in the electrolysis of water?

(A) The anode

(B) The electrode connected to the negative side of the battery

(C) The cathode

(D) Cannot be determined with the given information

37. Why is it necessary to add some salts to water for the electrolysis of water to proceed?

(A) Due to the production of acid during the electrolysis, a buffer is needed to maintain a constant pH.

(B) Water, as a poor electrical conductor needs some electrolyte solution to give the necessary conduction for the electrolysis to proceed.

(C) Salts are necessary to prevent the explosion of the dangerous gasses hydrogen and oxygen.

(D) Salts are not needed for the reaction to proceed.

38. Which of the following is NOT produced during the electrolysis of water?

(A) Electricity

(B) Acid

(C) Hydrogen

(D) Oxygen

39. Relative to the amount of oxygen produced, how much hydrogen gas is evolved during the electrolysis of water?

(A) 1.0 L

(B) Half as much

(C) The same amount

(D) Twice as much

40. If you added a drop of phenolphthalein during the electrolysis of water, at which electrode would you see the color change and why?

(A) The anode because phenolphthalein tests for the production of base

(B) The anode because phenolphthalein tests for the production of acid

(C) The cathode because phenolphthalein tests for the production of base

(D) The cathode because phenolphthalein tests for the production of acid

41. How long will it take 1.0 kg of Au to late from a solution of Au³⁺ with a current of 150 A?

(A) 54.4 minutes

(B) 2 hours 43 minutes

(C) 136 hours

(D) 2 days

42. How many grams of Pu (from Pu²⁺) will be plated onto a cathode in ten minutes with a current of 10 A?

(A) 7.6 g

(B) 15.2 g

(C) 3.8 g

(D) 0.76 g

43. A metal plates 1.41 g onto a cathode from a species in solution in 70 minutes with a current of 2.5 A. Identify the species.

(A) Na⁺

(B) Au³⁺

(C) Fe³⁺

(D) Cr⁴⁺

44. How long will it take to completely dissolve a silver anode whose mass is 3 g if a 2.0 A current is passed through it.

(A) 11.2 minutes

(B) 44.8 minutes

(C) 22.4 minutes

(D) 5.6 minutes

45. At STP, what volume of hydrogen gas is produced in the electrolysis of water is a current of 50 A is passes through a solution of pure water for 10 minutes?

(A) 3.48 L

(B) 0 L

(C) 6.96 L

(D) 1.74 L

46. At STP, what volume of hydrogen gas is produced in the electrolysis of water is a current of 50 A is passes through a solution of salt water for 10 minutes?

(A) 3.48 L

(B) 0 L

(C) 6.96 L

(D) 1.74 L

47. What is the molar mass of a substance that plates 5 g of itself in 10 minutes with a current of 10 A and requires 2 electrons per mole of that substance?

(A) 80.4 g / mol

(B) 321.6 g / mol

(C) 32.2 g / mol

(D) 160.8 g / mol

48. Given a solution with equal concentrations of the following species, using your chemical intuition, which one should plate first if the external potential is slowly increased from zero to larger values?

(A) Na

(B) Li

(C) Al

(D) Mg

49. Using your chemical intuition, what combination of elements would make a very powerful battery?

(A) F and Cl

(B) F and Li

(C) I and Fe

(D) Cd and Fe

50. Would a table of standard oxidation tables be just as valid as a table of standard reduction potentials and why?

(A) Yes, because they are the same.

(B) Yes, because the choice of writing reactions as reductions is purely arbitrary.

(C) No, because there is a physical basis for writing reactions as reductions.

(D) No, because the Nernst Equation tells us that equations should only be written as reductions.

Review of Stoichiometry

Review Test