Question

Which of the following species can function as both a Bronsted acid and a Bronsted base in water?
(1) $HCl{O}_4$
(2) $HC{O}_3^{-}$
(3) $HP{O}_4^{2-}$

• A. all 1, 2 and 3 are correct
• B. only 1 and 2 are correct
• C. only 2 and 3 are correct
• D. only 1 is correct
• E. only 3 is correct

Answer 1

The correct option is C only 2 and 3 are correct

$\left(1\right)$ $HCl{O}_4⟶Cl{O}_4^{-}+H^{+}$

Hence it acts only as Bronsted acid.

$\left(2\right)$ $H_{2}C{O}_3⟶H^{+}+HC{O}_3^{-}$

or $HC{O}_3^{-}+H^{+}⟶H_{2}C{O}_3$

and $HC{O}_3^{-}⟶H^{+}+C{O}_3^{2-}$

Hence, it acts as both a Bronsted acid and a Bronsted base.

$\left(3\right)$ $HP{O}_4^{2-}+H^{+}⟶H_{2}P{O}_4^{-}$

and $HP{O}_4^{2-}⟶H^{+}+P{O}_4^{3-}$

Here only $\left(2\right)$ and $\left(3\right)$ are correct.

A Bronsted acid donates a proton and a Bronsted base accepts a proton.