<P> The same half reactions can also be balanced with base as listed below . Not all half reactions must be balanced with acid or base . Many do, like the oxidation or reduction of water listed here . To add half reactions they must both be balanced with either acid or base . The acid - balanced reactions predominate in acidic (low pH) solutions, while the base - balanced reactions predominate in basic (high pH) solutions . </P> <Table> <Tr> <Td> Cathode (reduction): </Td> <Td> 2 H O (l) + 2e </Td> <Td> → </Td> <Td> H (g) + 2 OH (aq) </Td> </Tr> <Tr> <Td> Anode (oxidation): </Td> <Td> 4 OH (aq) </Td> <Td> → </Td> <Td> O (g) + 2 H O (l) + 4 e </Td> </Tr> </Table> <Tr> <Td> Cathode (reduction): </Td> <Td> 2 H O (l) + 2e </Td> <Td> → </Td> <Td> H (g) + 2 OH (aq) </Td> </Tr> <Tr> <Td> Anode (oxidation): </Td> <Td> 4 OH (aq) </Td> <Td> → </Td> <Td> O (g) + 2 H O (l) + 4 e </Td> </Tr>

The electrolysis of water forms h2 and o2