Question

$0.05$ mole of NaOH is added to $5$ litres of water. What will be the pH of the solution?

• A. $12$
• B. $7$
• C. $2$
• D. $10$

Answer 1

Answer: (A)

$12$

The NaOH is ionized to hydrated sodium ions and hydrated hydroxide ions.

$NaOH+H_{2}O\to N{a}^{+}+O{H}^{-}+H_{2}O+Heat$

$\left[NaOH\right]=\frac{0.05}{5}=0.01M$

$\left[O{H}^{-}\right]={10}^{-2}M$

$K_w=\left[H^{+}\right]\left[O{H}^{-}\right]$ is the ion product constant for water.

$\left[H^{+}\right]=\frac{k_w}{O{H}^{-}}=\frac{{10}^{-14}}{{10}^{-2}}={10}^{-12}$

$\therefore pH=12$