Water can act both as an acid and a base, and can do so even without the
presence of another species. The reaction between two water molecules is
or, more simply,
- 2H2O(l) < = > H3O+(aq) +
We can write the equilibrium
constant expression for the above reaction.
- H2O(l) < = > H+(aq) +
and solids do not enter into the expression.) For water at 250C,
the value of Kw is 1.0*10-14, which gives a concentration
of [H+] = [OH-] = 1.0*10-7 M in pure water.
- Kw = [H+][OH-]