Question

At $298K,$ the $pH$ of $0.23M$ weak acid $HX$ (ionization constant $=7.3\times 10^{-6}$ ) would be

• A. 11.47
• B. 2.88
• C. 3.88
• D. 4.88

Answer 1

Answer: (B)

For weak acid; $\alpha =\sqrt{\frac{K_a}{C}}$

$\left[H^{+}\right]=C\times \alpha =\sqrt{K_a\times C}=\sqrt{7.3\times 10^{-6}\times 0.23}=1.29\times 10^{-3}$

$pH=-\log H^{+}=\log \frac{1}{H^{+}}=\log \frac{1}{1.29\times 10^{-3}}=2.88$