# 20.9 Electrolysis

In a Galvanic/Voltaic Cell, a spontaneous redox reaction produces a current (electricity). In an electrolytic cell, electrical energy is needed to produce a chemical change. During electrolysis, the electrical energy forces a non-spontaneous reaction to occur.

20.9 Electrolysis

In an electrolytic process, we can use the stoichiometric relationships of an electrolytic process to calculate various electrolytic properties. In the first example shown below, we will calculate the mass of solid copper that is plated when a current of 10 amps is passed for 30 minutes through a Cu2+(aq) solution.

20.9 Stoich of Electrolytic Processes

The next example shows how long a current of 5 amps must be applied to a solution of Ag+ to produce 10.5 grams of Ag(s).

20.9 Electrolysis Example

Producing H2(g) has gained widespread attention from its potential application as a source of alternate energy. The following example shows why the electrolysis of water is not an effective way to produce hydrogen gas and shows how much hydrogen gas is liberated during the passage of 2 amps for 30 minutes.

20.9 Electrolysis of H2O

We can also calculate the concentration of a particular ion remaining in a solution after a current has been passed through its solution. In this case, the [Cu2+] remaining in 335 mL of solution that was originally 0.215 M copper(II) sulfate after the passage of 2.17 amps for 235 seconds, can be calculated.

20.9 Calculating Concentration in Electrolysis