for fixed temperature and pressure. Thus these water samples will be slightly acidic. If a pH of exactly 7.0 is required, it must be maintained with an appropriate buffer solution. See also Acid–base reaction Chemical equilibrium Molecular autoionization (of various solvents) Standard hydrogen electrode References External links General Chemistry – Autoionization of Water Ionization Water chemistry Equilibrium chemistry Water de:Protolyse#Autoprotolyse