Based on the equation pH = – log [H+],


Based on the equation pH = – log [H+], the pH of 10-8 mol dm-3 solution of HCl should be 8. However, it is observed to be less than 7.0. Explain the reason.


The solution is very dilute here and we know that HCl reacts with water to form hydronium ion. A decrease in pH can be observed as a result of a large concentration of

H+. Hydronium ion concentration also to be considered here.

Now total pH will be; [H3O+] = 10-8 + 10-7 M = 7

Hence the solution will be acidic.

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