On the basis of the equation `ph=-log[H^(+)]`,the ph of `10^(-8)` mol `dm^(-3)` solution of HCI should be 8. However, it is observed to be less than 7.0. Explain the reason.

Explanation

The pH of an acidic solution cannot be more than 7.0. whrneas the expected Ph is 8. To explain this it is suggested that `H^(+)` or `H_(3)O^(+)` ions are also released by the self ionisation of water.
Since water is neutral, `[H_(3)O^(+)]=10^(-7)M`.
`" therefore Total " [H_3O^(+)]" in solution "=10^(-8)M+10^(-7)M=10^(-8)[1+10]=11xx10^(-8)M`
`ph=-log[H_3O^(+)]=-[11xx10^(-8)]=[8-log11]`
`ph=[8-1.0411]=6.9586=6.96`.