Deck 16: Electrochemistry

Question 1

What is the best description of the following reaction?
PbO₂ (s) + H₂O (l) + 2 e^- → PbO (s) + 2 OH^- (aq)

A) Oxidation of PbO₂
B) Hydrolysis of PbO₂
C) Reduction of PbO₂
D) disproportionation of PbO₂

Answer 1

C

Question 2

The position of equilibrium for the cell
Cr₂O₇^2- (aq) + 6 Fe²⁺(aq) + 14 H⁺(aq) → 2 Cr³⁺ (aq) + 6 Fe³⁺ (aq) + 7 H₂O (l)
Favours the formation of products. Identify the half-cell processes that occur at the anode and cathode.

A) Cathode: Cr₂O₇^2-/Cr³⁺ Anode: Fe³⁺/Fe²⁺
B) Cathode: Cr³⁺/Cr²⁺ Anode: Fe³⁺/Fe
C) Cathode: Fe³⁺/Fe Anode: Cr³⁺/Cr²⁺
D) Cathode: Fe³⁺/Fe²⁺ Anode: Cr₂O₇^2-/Cr³⁺

Answer 2

A

Question 3

Determine the limiting molar conductivity of an aqueous solution of magnesium chloride, MgCl₂ (aq).

A) 3.0 mS m² mol^-1
B) 18.2 mS m² mol^-1
C) 25.8 mS m² mol^-1
D) 28.8 mS m² mol^-1

Answer 3

C

Question 4

The conductivity of an aqueous solution of ammonium sulphate, (NH₄)₂SO₄ (aq) is 0.316 S m^-1. Calculate the concentration of the solution.

A) 0.0110 mol dm^-3
B) 0.0148 mol dm^-3
C) 0.0091 mol dm^-3
D) 0.0898 mol dm^-3

Question 5

The conductivity of a solution of ethanoic acid, CH₃COOH, is
5)05 × 10^-4 S m^-1. Calculate the pH of the solution.

A) 1.9
B) 4.9
C) 3.3
D) 11.3

Question 6

The conductivity of a solution of methanoic acid, HCOOH, which was made by dissolving 0.921 g of acid in water and making up the volume to 1.00 dm³, was measured to be 5.05 × 10^-4 S m^-1 at a temperature of 298 K. Determine the acid dissociation constant of methanoic acid at this temperature.

A) 0.234
B) 1.82
C) 0.550
D) 0.192

Question 7

Use the data for the standard reduction potentials given in Table 17.2 to predict which of the following is the strongest oxidising agent in acidic solution: OCl^- (aq), Cr₂O₇^- (aq), H₂O₂ (aq) or MnO₄^- (aq)

A) OCl^- (aq)
B) Cr₂O₇^- (aq)
C) H₂O₂ (aq)
D) MnO₄^- (aq)

Question 8

By considering the standard reduction potentials given in Table 7.2, decide which of the following metals could be used as a sacrificial coating to protect nickel metal, Ni (s).

A) Copper, Cu (s)
B) Magnesium, Mg (s)
C) Silver, Ag (s)
D) Tin, Sn (s)

Question 9

Calculate the standard cell potential for the reaction
2 MnO₄^-(aq) + 5 Sn²⁺ (aq) + 16 H⁺ (aq) → 2 Mn²⁺ (aq) + 5 Sn⁴⁺ (aq) + 8 H₂O
At a temperature of 298 K.

A) -1.57 V
B) +1.37 V
C) +3.14 V
D) +2.29 V

Question 10

Determine the standard cell potential at 298 K for the reaction
2 OH^- (aq) + Cl₂ (g) → Cl^- (aq) + OCl^- (aq) + H₂O (l)
Using the data for the standard reduction potentials in Table 17.2.

A) +0.47 V
B) -0.94 V
C) +2.25 V
D) 0.00 V

Question 11

Determine the amount of electrical work that can be done by the system in the reaction
Cu (s) + Zn²⁺ (aq) → Cu²⁺ (aq) + Zn (s)
For which

A) -212 kJ mol^-1
B) -106 kJ mol^-1
C) -54 kJ mol^-1
D) -2.20 kJ mol^-1

Question 12

Determine the standard Gibbs energy change at 298 K for the reaction
Hg₂²⁺ (aq) + 2 Cl^- (aq) → Hg₂Cl₂ (s)
Using the data for the standard reduction potentials in Table 17.2.

A) -205 kJ mol^-1
B) -50 kJ mol^-1
C) +205 kJ mol^-1
D) -100 kJ mol^-1

Question 13

The standard Gibbs energy change for the reaction
H⁺ (aq) + OH^- (aq) → H₂O (l)
Is -80.1 kJ mol^-1 at 298 K. Determine the standard reaction potential for the cell
Pt (s) | O₂ (g) | H⁺ (aq) ║ OH^- (aq) | O₂ (g) | Pt (s)
At this temperature.

A) +0.83 V
B) +3.32 V
C) +0.21 V
D) +0.19 V

Question 14

Using the standard reduction potentials in Table 17.2 to calculate the equilibrium constant for the reaction
Fe³⁺ (aq) + V²⁺ (aq) → Fe²⁺ (aq) + V³⁺ (aq)
At a temperature of 298 K.

A) 1.3 × 10⁴⁰
B) 3.8 × 10^-18
C) 2.6 × 10¹⁷
D) 4.2 × 10⁸

Question 15

The standard cell potential for the reaction
6 [Fe(CN)₆]^3- (aq) + 2 Cr³⁺ (aq) + 7 H₂O (aq) → Cr₂O₇^2- (aq) + 14 H⁺ + 6 [Fe(CN)₆]^4- (aq)
Has a value of -0.97 V at 298 K. Predict whether the reaction, as written, will be spontaneous in the forward direction at this temperature.

A) The reaction is spontaneous in the forward direction
B) The reaction is at equilibrium
C) The reaction is spontaneous in the backward direction
D) It is not possible to determine from the standard cell potential alone, whether the reaction will be spontaneous

Question 16

Use the Nernst equation to calculate the cell potential for the cell
Al (s) | Al³⁺ (aq, c = 0.20 mol dm^-3) ║ Cu²⁺ (aq, c = 0.10 mol dm^-3) | Cu (s)
At a temperature of 298 K.

A) +1.98 V
B) +2.02 V
C) +0.02 V
D) +2.00 V

Question 17

Determine the change in standard Gibbs energy at 298 K for the reaction
PbO₂ (s) + Pb (s) + 2 H₂SO₄ (aq) → 2 PbSO₄ (aq) + 2 H₂O (l)
Which this basis of the lead-acid battery.

A) -394 kJ mol^-1
B) -197 kJ mol^-1
C) -163 kJ mol^-1
D) -201 kJ mol^-1

Question 18

A concentration cell is formed by dipping two copper, Cu (s) electrodes into copper sulfate, CuSO₄ (aq), solutions of different concentrations, and joining the half cells by a salt bridge. Determine the ratio of the concentrations of the copper sulfate solutions necessary to create a potential difference between the electrodes of 0.10 V.

A) 2400
B) 10
C) 6.1*10⁷
D) 1300

Question 19

Use the standard reduction potentials for the Ag(s)/AgCl(s) and Ag⁺(aq)/Ag(s) half cells in Table 16.2 to determine the solubility product of silver chloride, AgCl, at 298 K.

A) 1.8 * 10¹⁷
B) 5.6 * 10^-10
C) 6.4 *10⁹
D) 1.6 *10^-10

Question 20

Determine the limiting molar conductivity of an aqueous solution of ammonium chloride, NH₄Cl (aq).

A) 15.0 mS m² mol^-1
B) 22.6 mS m² mol^-1
C) 147.6 mS m² mol^-1
D) 14.8 mS m² mol^-1

Question 21

The standard cell potential for the reaction
2Al (s) + 3Sn²⁺(aq) → 2Al³⁺(aq) + 3Sn (s)
Has a value of +1.53 V at 298 K. Predict whether the reaction, as written, will be spontaneous in the forward direction at this temperature.

A) The reaction is spontaneous in the forward direction
B) The reaction is at equilibrium
C) The reaction is spontaneous in the backward direction
D) It is not possible to determine from the standard cell potential alone, whether the reaction will be spontaneous

Question 22

Determine the amount of electrical work that can be done by the system in the reaction
Ag⁺ (aq) + Fe²⁺ (aq) → Fe³⁺ (aq) + Ag (s)
Using the data provided in Table 16.2.

A) -152 kJ mol^-1
B) -32 kJ mol^-1
C) -2.9 kJ mol^-1
D) -28.9 kJ mol^-1

Question 23

Determine the standard Gibbs energy change at 298 K for the reaction
2Ag⁺ (aq) + Zn(s) $\rightarrow$ 2Ag(s) + Zn²⁺(aq)
Using the data for the standard reduction potentials in Table 16.2.

A) -7.7 kJ mol^-1
B) -301 kJ mol^-1
C) +135 kJ mol^-1
D) -150 kJ mol^-1

Question 24

Calculate the standard cell potential for the reaction
3 Zn(s) + Cr₂O₇²⁻ (aq) + 14 H⁺ (aq) → 3 Zn²⁺ (aq) + 2Cr³⁺ (aq) + 7 H₂O (l)
At a temperature of 298 K.

A) -0.57 V
B) +1.37 V
C) +3.61 V
D) +2.09 V