Question

A given weak acid (0.01 M) had $p{K}_a=6$. The pH of the solution is:

• A. 3
• B. 4
• C. 5
• D. 6

Answer 1

The correct option is B 4

${}_p{K}_a=6$

$HA\rightleftharpoons H^{+}+A^{-}$ $K_a$

0.01-x x x

$K_a=\frac{x^2}{0.01-x}={10}^{-6}$ $\therefore x\simeq {10}^{-4}$

$\therefore pH=-lo{g}_{10}\left[x\right]=4$