What is Electrolysis?
Electrolysis is a chemical technique that uses electric currents to drive otherwise non-spontaneous chemical reactions. By passing direct current (DC) through an electrolyte solution, we force oxidation reactions at the anode and reduction reactions at the cathode — depositing, dissolving, or converting substances in ways that would not happen without electrical energy.
Electrolysis powers many industries: electroplating metals (gold, silver, chromium), refining copper and aluminium, producing chlorine and hydrogen gas (chlor-alkali process), and splitting water into hydrogen and oxygen for fuel cells and green energy storage.
Faraday's Laws of Electrolysis
In the 1830s, Michael Faraday established two quantitative laws that govern electrolysis:
- First Law: The mass of substance deposited or dissolved at an electrode is directly proportional to the total electric charge passed through the electrolyte. m ∝ Q
- Second Law: When the same quantity of charge passes through different electrolytes, the masses of substances deposited are proportional to their equivalent masses (molar mass divided by valence). m ∝ M/n
How to Calculate Faraday's Law of Electrolysis
Combining both laws gives the fundamental electrolysis equation:
m = (M × I × t) / (n × F)
Where:
- m — mass of substance deposited or dissolved (grams)
- M — molar mass of the substance (g/mol)
- I — electric current (Amperes, A)
- t — time (seconds)
- n — number of electrons transferred per ion (valence)
- F — Faraday's constant = 96,485 C/mol (charge of one mole of electrons)
The electric charge Q = I × t (Coulombs). The number of moles deposited is moles = Q / (n × F), and the mass is m = moles × M.
Valence Numbers for Common Ions
| Ion | Element | Valence (n) | Molar Mass (g/mol) |
|---|---|---|---|
| Ag⁺ | Silver | 1 | 107.87 |
| Au⁺ | Gold (I) | 1 | 196.97 |
| Cu²⁺ | Copper (II) | 2 | 63.55 |
| Zn²⁺ | Zinc | 2 | 65.38 |
| Ni²⁺ | Nickel | 2 | 58.69 |
| Fe²⁺ | Iron (II) | 2 | 55.85 |
| Al³⁺ | Aluminium | 3 | 26.98 |
| Au³⁺ | Gold (III) | 3 | 196.97 |
| Fe³⁺ | Iron (III) | 3 | 55.85 |
| Cr³⁺ | Chromium (III) | 3 | 52.00 |
Electrolysis of Water
Water electrolysis splits H₂O into hydrogen and oxygen gas using direct current. The reactions are:
- Cathode (reduction): 2H⁺ + 2e⁻ → H₂ ↑
- Anode (oxidation): H₂O → ½O₂ + 2H⁺ + 2e⁻
For hydrogen: M = 2.016 g/mol, n = 2. For oxygen: M = 32.00 g/mol, n = 4. The theoretical minimum voltage to split water is 1.23 V; in practice, overpotential requires 1.8–2.0 V or more.
How to Use This Faraday's Law of Electrolysis Calculator
- Choose a unit system: Metric (SI) displays mass in grams; American (US Customary) displays mass in ounces (while showing grams as reference).
- Enter the electric current (I) in Amperes. This is the DC current flowing through your electrolytic cell.
- Enter the time and select the unit (seconds, minutes, or hours).
- Enter the molar mass (M) of the substance being deposited or dissolved in g/mol. See the table above for common values.
- Select the valence (n) — the number of electrons transferred per ion. For Cu²⁺ select 2; for Ag⁺ select 1; for Al³⁺ select 3, etc.
- Optional — Energy & Cost: Enter the applied voltage (V) and electricity price per kWh to calculate power consumption and operating cost. Choose your currency: USD ($), RUB (₽), EUR (€), GBP (£), or CNY (¥).
- Click Calculate to see charge (Q), moles deposited, mass, and atom count.
Frequently Asked Questions
What is Faraday's constant?
Faraday's constant F = 96,485 C/mol is the total electric charge carried by one mole of electrons (6.022 × 10²³ electrons, each with charge 1.602 × 10⁻¹⁹ C).
What is the difference between galvanic and electrolytic cells?
A galvanic cell (battery) converts chemical energy to electrical energy via a spontaneous reaction. An electrolytic cell does the reverse — it uses electrical energy to drive a non-spontaneous chemical reaction (electrolysis).
How does the valence affect the mass deposited?
Higher valence means more electrons are needed per ion, so less mass is deposited for the same charge. Aluminium (n = 3) requires three times more charge per mole than silver (n = 1).
Can I calculate electrolysis for water splitting?
Yes. For hydrogen gas (H₂): set M = 2.016 g/mol and n = 2. For oxygen gas (O₂): set M = 32.00 g/mol and n = 4. Enter voltage ≥ 1.8 V for a realistic operating cost estimate.