At 25∘C the pH of a 10−8 molar solution of HCl in water is
Between 6 and 7
When the solution is highly diluted and the concentration of acid is very less, we cannot neglect the concentration of [H+] of water. In such cases [H+]total would be calculated as follows.
[H+]total=[H+]acid+[H+]water=10−8+10−7 Since[H+] in water is10−7 molL−1 at 25∘ C=10−7(0.1+1)=1.1×10−7pH=−log [H+]=−log[1.1×10−7]=6.9581
Hence pH will be less than 7. Just slightly acidic between 6-7