ph of a solution of a strong acid is 5.0.What will be the ph of the solution obtained after dilluting the given solution to 100 times ?

Explanation

pH = 5 means `[H^(+)]=10^(-5)M`. On diluting 100 times , `[H^(+)]=(10^(-5))/(100) = 10^(-7) M`.
This should give pH = 7 but it cannot be so because solution is acidic and pH should be less than 7 The reason is that `[H^(+)]` from `H_(2)O` cannot be neglected. Thus, total `[H^(+)]=10^(-7)M` (from HCl) + `10^(-7)` M (from `H_(2)O ` ) `= 2xx10^(-7)M`
`:. pH = - log (2xx10^(-7))=7-0.3010 = 6.699`.