The pH of a 10 –9 M solution of HCl in water is

For 9 10 MHCl , concentration of acid is quite less. Whenever, H from strong acid is 6 10 M, contribution of 2 H O is to be added. Thus, 2 H O H OH HCl H Cl -> Total, 2 solution HCl H O H H H Using charge balance relation, H Cl OH 9 w 2 9 w K H 10 H H 10 H K >> x Let,  H be  x Then, 2 9 14 x 10 x 10 x Solving for  x 7 x 1.01 10 x Thus,  pH log H 7 [H ] 1.01 10 x = 6.9