Faraday's Law of Electrolysis Calculator
Mass of metal deposited or gas evolved from current and time — or the time and charge needed for a target mass — for any ion with its molar mass and charge, with efficiency and gas volume at STP.
How it works
m = (I·t ÷ F) × (M ÷ z) × efficiency, F = 96,485 C/mol; t = m·z·F ÷ (I·M·η)
Faraday found that the mass produced at an electrode is proportional to the charge passed and to the molar mass divided by the number of electrons each ion needs — one faraday (96,485 C) deposits one equivalent. That makes electroplating and refining exactly predictable: 1 A for 1 hour deposits 1.19 g of copper or 4.02 g of silver. Real cells run below 100% current efficiency because side reactions (hydrogen evolution, for instance) consume some of the charge.
Worked example
2.5 A for 60 minutes = 9,000 C = 0.0933 mol e⁻; copper (z = 2) gives 0.0466 mol = 2.96 g at 100% efficiency.
Frequently asked questions
How many electrons for water electrolysis?
2 per H₂ and 4 per O₂ — so hydrogen is produced at twice the molar rate of oxygen.
Why is aluminium so energy-hungry?
Three electrons per atom of a light metal: 1 kg needs 3 × 96,485 × 37 mol ≈ 10.7 million coulombs, at 4 V about 12 kWh.
Related calculators
For study and planning — check units and conditions against your data source before using a result in the lab.