Q. Which one of the following species acts as both Bronsted acid and base?
A) $H_{2}PO_{2}^{-}$
B) $HPO_{3}^{2 -}$
C) $HPO_{4}^{2 -}$
D) All of these
Explanation
(c)
$HPO_{4}^{2 -} + H_{2}O \rightleftharpoons H_{2}PO_{4}^{2 -} + {OH}^{-}$
$HPO_{4}^{2 -} + H_{2}O \rightleftharpoons PO_{4}^{3 -} + H_{3}O^{+}$
$H_{2}PO_{2}^{-}\$ is a conjugate base of $H_{3}{PO}_{2}\$(a monobasic acid) and does not give $H^{+},\ HPO_{3}^{2 -}$ is a conjugate base of $H_{2}PO_{3}^{-}\$ and does not ionise further, since $H_{3}PO_{3}$ is a dibasic acid.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.