Question

Which of the following is the weakest acid?

• A. Phenol $(K_a=1.3\times {10}^{-10})$
• B. Hydrocyanic acid $(K_a=4.9\times {10}^{-10})$
• C. Acetic acid $(K_a=1.8\times {10}^{-10})$
• D. Benzoic acid $(K_a=6.5\times {10}^{-10})$

Answer 1

The correct option is A Phenol $(K_a=1.3\times {10}^{-10})$

A large Ka value indicates a strong acid because it means the acid is largely dissociated into its ions.

A small Ka value means little of the acid dissociates, then it is a weak acid.

$\therefore$ Phenol is the weakest acid.

Hence, option $\left(A\right)$ is correct.