Calculate product mass from electrolysis charge.
Faraday's laws of electrolysis say the amount of substance liberated at an electrode is proportional to the charge passed, and inversely proportional to the number of electrons each ion needs. Charge is current times time in seconds; dividing by the Faraday constant of 96,485 C per mole of electrons gives moles of electrons, and dividing again by z gives moles of product. That second division is the step most often missed: copper plating from Cu2+ requires two electrons per atom, so the same charge that deposits 1.12 g of copper would deposit 2.24 g of silver from Ag+, despite silver's higher molar mass. Voltage does not appear anywhere — it governs whether the reaction proceeds and how fast, but the yield is set entirely by charge.
Faraday's law of electrolysis
Charge Q = current x time in seconds; moles of product = Q / (96,485 x z); mass = moles x molar mass; equivalent mass = molar mass / z
Because it divides the yield directly. Getting z wrong by a factor of two halves or doubles the predicted mass — aluminium from Al3+ needs three times the charge per mole that a monovalent metal does, which is why smelting it is so energy-intensive.
Faraday's law depends only on charge. Voltage must exceed the decomposition potential for anything to happen, and it determines power consumption, but it does not change how much metal a given number of coulombs deposits.
Usually slightly less. Real cells lose some current to side reactions such as hydrogen evolution, so multiply by the current efficiency — often 90-99% for metal plating, lower for gas-evolving processes.