The pH of a solution is 5.0. To a 10 ml of this solution, 990 ml of water is added. Then the pH of the resulting solution is

V1N1=V2N2; 1010-5=10+990N2; N2=10-7 M ;When the concentration of the acid or base is less than equal to 10-7 M, then [ H+] or [OH-] furnished from water is also taken into accout.H+=10-7acid+10-7water ; H+=2×10-7; pH=7-log2=6.7 ;