A Handbook for Teachers of Chemistry, Vol.4.
Water is decomposed into hydrogen and oxygen gases using electricity.
A Hoffman electrolysis apparatus collects the two gases separately and shows the 2 to 1 ratio nicely. If a pH indicator is used the anode becomes yellow and cathode becomes blue. Hydrogen gas can be burned to produce a small pop sound and the oxygen can be used to re-ignite a glowing wooden splint. The solution becomes acidic at the anode and basic at the cathode. Be careful of explosive hydrogen and oxygen mixtures.