All electrical laws
Faraday's second law of electrolysis
When the same quantity of charge passes through different electrolytes, the masses liberated are proportional to their chemical equivalent weights.
m₁ / m₂ = E₁ / E₂
- m₁, m₂
- masses liberated in each electrolyte (kilograms)
- E₁, E₂
- chemical equivalent weights (molar mass ÷ valency)
In plain English: Pass the same charge through silver and copper cells in series: you get more grams of silver because each silver ion needs only one electron while copper needs two, and silver atoms are heavier.
Where you'll meet it: The classic series-cells exam problem, and how the coulomb (and the ampere before 2019) was once defined — by weighing deposited silver.