Faraday’s Law: Calculate Mass Deposited

Question

How many grams of copper metal will be deposited from a solution that contains Cu^2+ ions if a current of 0.788 A is applied for 70.7 minutes.

 _____grams

Answer 1

0.788 A for 70.7 minutes corresponds to 0.788 x 70.7 x 60 = 3.34 x 10³ coulombs of charge. Faraday's constant is 96,485 C / mole of electrons. Inverting this you get 1 mole electrons / 96485 C. The number of moles of electrons is then 1/96485 x 3.34 x 10³ = 3.46 x 10-2 moles of electrons.

Cu²⁺ can acquire 2 moles electrons per mole of Cu.

1 mole Cu / 2 moles electrons x 3.46 x 10^-2 moles electrons = 1.73 x 10^-2 moles Cu.

63.5 g / mole Cu x 1.73 x 10^-2 moles Cu = 1.10 g Cu