Q. An aqueous solution of sodium carbonate has a pH greater than 7 because
A) It contains more carbonate ions than $H_{2}O$ molecules
B) Contains more hydroxide ions than carbonate ions
C) $Na^{+}$ ions react with water
D) Carbonate ions react with $H_{2}O$
Explanation
(b)
$Na_{2}CO_{3} + H_{2}O \rightarrow 2NaOH + H_{2}CO_{3}$
$\because\ \ \ NaOH\ is\ strong\ base.$
$\therefore$ It will be more ionised and number of $Na^{+}\ and\ OH^{-}\ ions\ will\ be\ more$.
$\because H_{2}CO_{3}\ is\ weak\ acid$ .
$\therefore$ It will be less ionised and number of $H^{+}\ and\ CO_{3}^{2 -}$ will be less.
$\therefore$ The solution will have more hydroxide ions than carbonate ions.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.