MODEL RELEASED. Electrolysis of water. Students observing the electrolysis of water (H2O) with a Hoffman apparatus. Electrolysis uses an electrical current (from the power pack at lower left) to decompose a chemical, in this case water, into its constituent parts. The decomposition occurs at the two electrodes (base of the glassware), producing oxygen (O2) and hydrogen (H2) gases at the anode electrode (left) and cathode electrode (right) respectively. The equation for the reaction is: 2 H20 ----> 2 H2 + O2 As expected, and observed at centre left, twice as much hydrogen gas as oxygen gas is produced.