On the basis of 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.

Question

On the basis of 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.

Philoid · Accepted Answer

From the given concentration we can conclude that the solution is very dilute and we know when HCl reacts with water it forms hydronium ion hence, the resulting large concentration of (H+) leads to a decrease in the pH. So, here we cannot neglect the concentration of H₃O⁺ ions produced in the solution. We have to take its concentration into account.

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

Hence the solution will be acidic.

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

Hence the solution will be acidic.

On the basis of 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.

On the basis of 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.