Electrochemistry Practice Test

This is about how the mass of material deposited during electroplating or a redox process relates to the total electric charge passed, using Faraday’s law. The amount of substance deposited is directly proportional to the charge, with the proportionality constant built from the molar mass, the number of electrons needed to deposit one atom (or ion), and Faraday’s constant. Specifically, for a deposit with molar mass M that requires n electrons per atom, the charge needed to deposit one mole of atoms is nF. Therefore, the number of moles deposited for a total charge Q is Q divided by nF. Multiplying by the molar mass M converts that to mass, giving m = M Q /(n F). This shows why the linear form with Q in the numerator and n and F in the denominator correctly describes the relationship. If you tried to put n in the numerator or square F or use Q^2, you’d violate the linear dependence on charge and the units, leading to an incorrect amount. The correct expression is m = (M Q)/(n F).