Explanation:
[tex]KOH→K {}^{ + } + OH {}^{ - } \\ [OH {}^{ - } ] = 3.4 \times {10}^{ - 3} \\ k _{w} = [OH {}^{ - } ] [H {}^{ + } ] \\ 1 \times {10}^{ - 14} = 3.4 \times {10}^{ - 3} \times [H {}^{ + } ] \\ [H {}^{ + } ] = 2.94 \times {10}^{ - 12} \: M[/tex]
