Assertion: pH of 10–8 M HCl lies between 6 and 7. Reason:  For  very  dilute  solutions  of  acids,  H⁺  ion contribution from water is also taken into consideration.

For 8 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 IONIC EQUILIBRIUM 67 8 w 2 8 w K H 10 H H 10 H K >> x Let,  H be  x Then, 2 8 14 x 10 x 10 x Solving for  x 7 x 1.05 10 x Thus,  pH log H 6.98