Question

What is the pH of 0.02 M Sodium Hydroxide solution?

• A. 1.7
• B. 12.0
• C. 2.0
• D. 12.3

Answer 1

The correct option is D 12.3

Since sodium hydroxide is a strong base, it will dissociate completely in water. This means that the concentration of the base will be equal to the concentration of hydroxide ions after the reaction runs to completion.
$NaOH\left(aq\right)\rightleftharpoons N{a}^{+}+O{H}^{-}0.02M0.02M$
Since 1 hydroxide ion is created from each molecule of sodium hydroxide that dissociates , hence 0.02 M NaOH will give 0.02 M of hydroxide ions.
$pOH=-lo{g}_{10}(OH{)}^{-}=-lo{g}_{10}(0.02)pOH=1.70pH+pOH=14\Rightarrow pH=14-1.70=12.3pH=12.3$