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What are Faraday's Laws of Electrolysis?

Faraday's laws of electrolysis describe how electric charge drives chemical change. The first law links charge to moles of product; the second law compares products from different substances under the same charge.

Short answer

Faraday's first law: moles of substance = Q / (nF), where Q is charge (C), n is electrons, F is Faraday's constant (96485 C/mol). Mass deposited is proportional to current and time.

Faraday's First Law: Charge → Moles of Product

1
Apply current I (amperes)
Charge flows through solution.
↓
2
Measure time t (seconds)
Q = It (coulombs).
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3
Count electrons n per product
Cu²⁺ + 2e⁻ → Cu: n=2.
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4
Calculate moles
moles = Q/(nF) = It/(nF).
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5
Convert to mass
mass = moles × molar mass (g/mol).

Try it: interactive calculator

Moles of product

0.006mol

= (2*600)/(2*96485)

Current I2 ATime t600 sElectrons transferred2

Step-by-step worked examples

Electrolyzing CuSO₄ with 2 A for 10 min, how many moles of Cu deposited? (n=2)

Q = It = 2 A × 600 s = 1200 C
Cu²⁺ + 2e⁻ → Cu
moles = Q/(nF) = 1200/(2×96485)
moles = 1200/192970 = 0.00622 mol

If 0.5 mol of Ag deposits (1 e⁻ per Ag⁺), what charge passed?

Ag⁺ + e⁻ → Ag, so n=1
Q = moles × n × F
Q = 0.5 × 1 × 96485
Q = 48242.5 C

Electrolyze AgNO₃ at 3 A for 5 min. How much Ag (M=107.9 g/mol) deposits?

Q = It = 3 × 300 = 900 C
moles Ag = Q/(nF) = 900/(1×96485) = 0.00933 mol
mass = 0.00933 × 107.9 = 1.007 g ≈ 1.01 g

Flashcards

Quick quiz

Q1.Moles of Cu deposited from CuSO₄ if Q = 1000 C and n = 2?

Correct answer: B. moles = Q/(nF) = 1000/(2×96485) ≈ 0.00519 mol.

Q2.Which has the second law of electrolysis identified?

Correct answer: B. Faraday's second law: under equal charge, moles of product ∝ (molar mass / n).

Q3.Faraday constant F equals…

Correct answer: B. F = N_A × e (Avogadro's number × electron charge) ≈ 96485 C/mol.

Q4.Electrolyze for 1 hour at 1 A. If n=3, what is Q?

Correct answer: A. Q = It = 1 A × 3600 s = 3600 C (time in seconds).

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Common mistakes

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Faraday's law ignores the type of ion being electrolyzed. — Correct: Different ions deposit different masses for the same charge (second law).

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Charge Q is just the current. — Correct: Charge is current × time: Q = It (in coulombs, not just amperes).

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Faraday constant F is different for every experiment. — Correct: F = 96485 C/mol is a universal physical constant.

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n is the number of moles deposited. — Correct: n is the number of electrons transferred per ion (e.g., Zn²⁺ needs 2e⁻).

FAQ

What are Faraday's laws of electrolysis?

First law: moles of product = Q/(nF). Second law: under equal charge, different ions deposit masses inversely proportional to their charge per ion.

How do I calculate moles from charge?

moles = Q/(nF), where Q is coulombs, n is electrons per ion, F is 96485 C/mol.

How do I find mass of metal deposited?

mass = moles × molar mass = [Q/(nF)] × M.

What is Faraday's second law?

Under the same charge, moles of different products are proportional to their (molar mass / charge per ion).