Question

pH of 10⁻⁸ M HCl solution is:

• A. 8
• B. Greater than 7, less than 8
• C. Greater than 8
• D. Greater than 6, less than 7

Hint:

For very dilute strong acids, account for the autoionization of water when calculating pH.

Answer 1

The Correct Option is D

The HCl solution has a concentration of \(10^{-8}\) M. As HCl is a strong acid, its contribution to [H⁺] is \(10^{-8}\) M. Water autoionization also produces [H⁺] = \(10^{-7}\) M. The total [H⁺] is:

\( \text{Total} [\text{H}^+] = 10^{-8} + 10^{-7} \approx 1.1 \times 10^{-7} \text{ M} \)

The pH is calculated as follows:

\( \text{pH} = -\log[\text{H}^+] \approx -\log(1.1 \times 10^{-7}) \approx 6.96 \)

Therefore, the pH falls between 6 and 7.