Electrolysis

To solve this type of stoichiometry problems, we need the following steps:

1.Current and time

2.Quantity of charge in coulombs

3.Moles of electrons

4.Moles of copper

5.Grams of copper

For example, given the equation:

Ag+ (aq) + e- --> Ag (s)

How many grams of Ag can be produced in 30.0 minutes with a current of 10.0 A?

Using the steps written above, we can find how many grams of silver is produced when given an amount of time and current (in amps)

Coulombs of charge = amps x seconds = (C/s) x s

= 10.0 C/s x 30 min x 60 s/min

= 1.80 x 10^4 C

1.Calculate number of moles of electrons required to carry 1.80 x 10^4 coulombs of charge

1.80 x 104 C x 1 mol e- / 96845 C = 1.87 x 10-1 mol e-

Meaning that there are 0.187 mole of electrons flowed into the Ag+ solution

2.Each Ag+ ion requires one electron to become a silver atom. Thus each mole of electrons produces 1 mole of silver metal. (mol ratio)

1.87 x 10-1 mol e- x 1 mol Ag/1 mol e- = 1.87 x 10-1 mol Ag

3.We now know the moles of silver metal plated onto the cathode, and we can calculate the mass of silver formed:

1.87 x 10-1 mol Ag x 107.9 g / mol = 20.2 g Ag