AP Electrochemistry 2

Question 1

Calculate the standard cell potential (E°cell) for the galvanic cell: Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s). Given: E°(Zn²⁺/Zn) = −0.76 V and E°(Cu²⁺/Cu) = +0.34 V.

Accepted Answer

+1.10 V

Answer

E°cell = E°cathode − E°anode = (+0.34) − (−0.76) = +1.10 V. Cu²⁺ is reduced at the cathode; Zn is oxidized at the anode.

Question 2

Using the Nernst equation, what is the cell potential at 25°C for the Zn-Cu cell when [Zn²⁺] = 2.0 M and [Cu²⁺] = 0.010 M? (E°cell = 1.10 V, n = 2)

Accepted Answer

1.04 V

Answer

Q = [Zn²⁺]/[Cu²⁺] = 2.0/0.010 = 200. E = E° − (0.0592/n)logQ = 1.10 − (0.0296)log(200) = 1.10 − (0.0296)(2.301) = 1.10 − 0.068 = 1.03 ≈ 1.04 V.

Question 3

In the electrolysis of molten NaCl, which species is produced at each electrode?

Accepted Answer

Cathode: Na metal; Anode: Cl₂ gas

Answer

In electrolysis, the cathode is negative and attracts Na⁺ (reduction: Na⁺ + e⁻ → Na). The anode is positive and attracts Cl⁻ (oxidation: 2Cl⁻ → Cl₂ + 2e⁻).

Question 4

How many grams of copper (MM = 63.55 g/mol) are deposited during the electrolysis of a CuSO₄ solution when a current of 2.50 A flows for 30.0 minutes? (F = 96,485 C/mol e⁻)

Accepted Answer

1.48 g

Answer

Charge = I × t = 2.50 × (30.0 × 60) = 4500 C. mol e⁻ = 4500/96485 = 0.04663 mol. Cu²⁺ + 2e⁻ → Cu, so mol Cu = 0.04663/2 = 0.02332 mol. Mass = 0.02332 × 63.55 = 1.48 g.

Question 5

Which of the following best describes the role of the salt bridge in a galvanic cell?

Accepted Answer

It allows ions to flow between half-cells to maintain electrical neutrality without mixing the solutions

Answer

As the cell operates, charge builds up in each half-cell (Zn²⁺ accumulates at the anode; Cu²⁺ depletes at the cathode). The salt bridge allows ions (typically K⁺ and NO₃⁻) to migrate to neutralize these charges without mixing the electrode solutions.

AP Practice Test

AP Practice Test

AP Electrochemistry 2