Question

An acid having pH = 6 is diluted 1000 times. What will be the pH of the final solution ?

Answer 1

pH = 6 means `[H_(3)O^(+)=10^(-6)M`.
After diluting 1000 times, `[H_(3)O^(+)]=10^(-6)//1000M = 10^(-9)M`.
`:. [H_(3)O^(+)]` from `H_(2)O` cannot be neglected.
Total `[H_(3)O^(+)]=10^(-9)+10^(-7)(10^(-2)+1)=10^(-7)(1.01)`
`:. pH = - log (1.01xx10^(-7))=7-0.0043=6.9957`.