Question

The ionization constant of phenol is $1.0\times 10^{-10}.$ Thus, $pH$ of a mixture of $0.05M$ phenolate ion and $0.01M$ phenol solution, is

• A. 10.7
• B. 1.0
• C. 5.0
• D. 11.2

Answer 1

Answer: (A)

$K_a=\frac{[B]\left[H_3{O}^{+}\right]}{0.01}$

$1.0\times 10^{-10}=\frac{0.05\times \left[H_3{O}^{+}\right]}{0.01}$

$\therefore \left[H_3{O}^{+}\right]=\frac{1.0\times 10^{-10}}{5}=2\times 10^{-11}$
$\therefore pH=-\log \left[H_3{O}^{+}\right]=-\log \left(2\times 10^{-11}\right)$

$pH=10.7$