Electrolysis Reactions

In electrolysis, the ions in the electrolyte go to the oppositely charged electrode. This means the cations go to the cathode, and the anions go to the anode. At the electrodes, these ions take part in chemical reactions called redox reactions.

A redox reaction is a chemical reaction where electrons are exchanged between chemical substances. In a redox reaction, one chemical substance gains electrons in a reduction reaction, and one chemical substance loses electrons in an oxidation reaction. Since both reduction and oxidation reactions occur, we call the overall reaction a redox reaction!

Figure 1 shows an electrolytic cell that produces hydrogen and oxygen from water. The redox reactions at the electrodes produce hydrogen and oxygen gas.

The reduction reaction at the negative cathode is: 2H+ + 2e- → H2two hydrogen cations and two electrons go to, one molecule of hydrogen. In this reaction, hydrogen cations gain electrons to become hydrogen gas.

The oxidation reaction at the positive anode is: 2OH- → ½ O2 + H2O + 2e-two hydroxide anions goes to, half a molecule of oxygen, one water molecule, and two electrons. In this reaction, two hydroxide anions lose two electrons to become water and oxygen gas.

Figure 1 - An electrolytic cell that turns water into hydrogen and oxygen gas.