AP Chemistry Practice Quiz: Electrolysis and Faraday's Law

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

Which of the following best describes the process of electrolysis?

A)A process that generates electrical energy from a spontaneous chemical reaction.B)A process that uses electrical energy to drive a non-spontaneous chemical reaction.C)A process where a catalyst is used to speed up a spontaneous redox reaction.D)A process that measures the voltage of a reaction at equilibrium.

All Questions (10)

Which of the following best describes the process of electrolysis?

A) A process that generates electrical energy from a spontaneous chemical reaction.

B) A process that uses electrical energy to drive a non-spontaneous chemical reaction.

C) A process where a catalyst is used to speed up a spontaneous redox reaction.

D) A process that measures the voltage of a reaction at equilibrium.

Correct Answer: B

The provided content explicitly states that 'Electrolysis is the process of using an external electrical energy source to drive a thermodynamically unfavorable (non-spontaneous) redox reaction.'

An electrolytic cell operates with a constant current of 4.0 Amperes for 500 seconds. What is the total charge, in Coulombs, that passes through the cell?

A) 125 C

B) 496 C

C) 2000 C

D) 96,485 C

Correct Answer: C

According to Faraday's Law, the charge (q) is the product of the current (I) and time (t). Using the equation q = I × t, we get q = 4.0 A × 500 s = 2000 C.

A current of 3.00 A is passed through a solution containing Ag⁺ ions for 20.0 minutes. What mass of silver metal (Molar Mass ≈ 108 g/mol) is produced? The half-reaction is Ag⁺(aq) + e⁻ → Ag(s).

A) 2.02 g

B) 4.03 g

C) 6.05 g

D) 12.1 g

Correct Answer: B

First, calculate the total charge: q = I × t = 3.00 A × (20.0 min × 60 s/min) = 3600 C. Next, convert charge to moles of electrons: 3600 C / 96,485 C/mol e⁻ = 0.0373 mol e⁻. The stoichiometry is 1 mol Ag per 1 mol e⁻, so 0.0373 mol of Ag is produced. Finally, convert moles to mass: 0.0373 mol Ag × 108 g/mol = 4.03 g Ag.

During the electrolysis of molten MgCl₂, a current of 10.0 A is applied for 965 seconds. How many grams of magnesium metal (Molar Mass ≈ 24.3 g/mol) are produced? The half-reaction is Mg²⁺ + 2e⁻ → Mg.

A) 0.61 g

B) 1.22 g

C) 2.43 g

D) 4.86 g

Correct Answer: B

First, calculate the total charge: q = I × t = 10.0 A × 965 s = 9650 C. Convert charge to moles of electrons: 9650 C / 96,485 C/mol e⁻ ≈ 0.100 mol e⁻. The half-reaction shows that 2 moles of electrons are required to produce 1 mole of Mg. So, moles of Mg = 0.100 mol e⁻ × (1 mol Mg / 2 mol e⁻) = 0.0500 mol Mg. Finally, calculate the mass: 0.0500 mol Mg × 24.3 g/mol = 1.215 g, which is approximately 1.22 g.

How long, in seconds, must a current of 5.00 A be passed through a solution of AuCl₃ to produce 10.0 g of gold (Molar Mass ≈ 197 g/mol)? The half-reaction is Au³⁺(aq) + 3e⁻ → Au(s).

A) 979 s

B) 1470 s

C) 2940 s

D) 8790 s

Correct Answer: C

First, work backward from mass to charge. Moles of Au = 10.0 g / 197 g/mol = 0.05076 mol Au. Moles of electrons needed = 0.05076 mol Au × (3 mol e⁻ / 1 mol Au) = 0.1523 mol e⁻. Total charge needed = 0.1523 mol e⁻ × 96,485 C/mol e⁻ = 14,700 C. Finally, calculate time: t = q / I = 14,700 C / 5.00 A = 2940 s.

In an electrolytic process, a constant current is applied for a fixed amount of time, producing X grams of a substance. If the experiment is repeated under identical conditions but for twice the duration, what mass of the substance will be produced?

A) 0.5 * X grams

B) X grams

C) 2 * X grams

D) 4 * X grams

Correct Answer: C

According to Faraday's Law (q = I × t), the total charge passed is directly proportional to the time. Since the amount of substance produced is directly proportional to the charge, doubling the time (t) while keeping the current (I) constant will double the charge (q) and therefore double the mass of the substance produced to 2 * X grams.

The same quantity of electrical charge that deposits 1.0 mole of silver (Ag) from an Ag⁺ solution is passed through a solution containing Cu²⁺ ions. How many moles of copper (Cu) will be deposited? (Half-reactions: Ag⁺ + e⁻ → Ag; Cu²⁺ + 2e⁻ → Cu)

A) 0.5 mol

B) 1.0 mol

C) 2.0 mol

D) 4.0 mol

Correct Answer: A

To deposit 1.0 mole of Ag, 1.0 mole of electrons is required based on the 1:1 mole ratio in the half-reaction. This same amount of charge (1.0 mole of electrons) is passed through the Cu²⁺ solution. The half-reaction for copper shows a ratio of 1 mole of Cu for every 2 moles of electrons. Therefore, the moles of Cu deposited will be 1.0 mol e⁻ × (1 mol Cu / 2 mol e⁻) = 0.5 mol Cu.

What mass of aluminum (Molar Mass ≈ 27.0 g/mol) is produced by the electrolysis of molten Al₂O₃ in 1.00 hour with a constant current of 10.0 A? The half-reaction is Al³⁺ + 3e⁻ → Al.

A) 1.01 g

B) 3.36 g

C) 9.00 g

D) 10.1 g

Correct Answer: B

First, convert time to seconds: 1.00 hr × 3600 s/hr = 3600 s. Calculate charge: q = I × t = 10.0 A × 3600 s = 36,000 C. Calculate moles of electrons: 36,000 C / 96,485 C/mol e⁻ = 0.373 mol e⁻. Use the mole ratio (1 mol Al : 3 mol e⁻): 0.373 mol e⁻ × (1 mol Al / 3 mol e⁻) = 0.124 mol Al. Finally, calculate mass: 0.124 mol Al × 27.0 g/mol = 3.36 g.

In an electrolytic cell, 1.59 g of copper (Molar Mass ≈ 63.5 g/mol) is deposited from a Cu²⁺ solution in 25.0 minutes. What was the average current used, in Amperes? The half-reaction is Cu²⁺ + 2e⁻ → Cu.

A) 1.61 A

B) 3.22 A

C) 4.82 A

D) 6.43 A

Correct Answer: B

First, calculate moles of Cu: 1.59 g / 63.5 g/mol = 0.0250 mol Cu. Next, find moles of electrons using the mole ratio (2 mol e⁻ : 1 mol Cu): 0.0250 mol Cu × (2 mol e⁻ / 1 mol Cu) = 0.0500 mol e⁻. Calculate the total charge: 0.0500 mol e⁻ × 96,485 C/mol e⁻ = 4824 C. Convert time to seconds: 25.0 min × 60 s/min = 1500 s. Finally, calculate current: I = q / t = 4824 C / 1500 s = 3.22 A.

Which set of variables is related by the Faraday constant (F ≈ 96,485 C/mol e⁻)?

A) Current and time

B) Charge and moles of a substance

C) Charge in Coulombs and moles of electrons

D) Current and moles of electrons

Correct Answer: C

The Faraday constant is the conversion factor that relates the total electrical charge (in Coulombs) to the number of moles of electrons that have been transferred. Its units are Coulombs per mole of electrons (C/mol e⁻).