What is the pH of 10-9 M HCl?
Here , [H+] for acid is < 10 -7 { which is not possible }
so,
total [H+] = 10 -7 + 10 -9
= 1.01 x 10 -7
Thus, pH = - log [H+]
= 6.99
State common ion effect.
The phenomena of suppressing the ion concentration or ionic product of a weak electrolyte by a stronger electrolyte when they yield at least a common ion together in a solution is called common ion effect.
eg, When HCN is mixed in water with HCl , the ionic product of HCN is suppressed.