Question

What is the conjugate base of ${\text{HPO}}_4^{2 - }$ ?

Answer 1

Hint: To determine the conjugate base of ${\text{HPO}}_4^{2 - }$ we should know what conjugate base it and how to determine the conjugate base. The acid after donating a proton is known as a conjugate base because the anion formed by the acid can accept a proton now, so it acts as a base now.

Complete step-by-step answer:According to the Bronsted-Lowery concept, acids are proton donors and bases are proton acceptors. The acid and base react to form conjugate base and conjugate acid.Acid forms conjugate base and base forms conjugate acid.The general reaction of acid and base is shown as follows:
Acid\[ + \]Base$ \to $ conjugate base\[ + \]conjugate acid
We have to determine the conjugate base of ${\text{HPO}}_4^{2 - }$ it means ${\text{HPO}}_4^{2 - }$ is acting as an acid. The acid loses a proton to form a conjugate base, so, ${\text{HPO}}_4^{2 - }$ will lose a proton to form a conjugate base.
The conjugate base of ${\text{HPO}}_4^{2 - }$ is shown as follows:
Acid $ \to $ conjugate base\[ + \]proton
\[{\text{HPO}}_4^{2 - }\, \to \,{{\text{H}}^ + }\, + \,\,{\text{PO}}_4^{3 - }\,\]
The acid ${\text{HPO}}_4^{2 - }$ after losing a proton forms the conjugate base \[{\text{PO}}_4^{3 - }\,\].
\[{\text{PO}}_4^{3 - }\,\] is the conjugate base of ${\text{HPO}}_4^{2 - }$ .
Therefore, \[{\text{PO}}_4^{3 - }\,\] is the correct answer.

Note: The acid is known as the conjugate base after losing a proton so, if acid is strong its conjugate base will be weak because in that case, acid has a high tendency to dissociate. Similarly, the base is known as the conjugate acid after accepting a proton so, if a base is strong its conjugate acid will be weak because in that case, the base has a high tendency to accept a proton. The strength of an acid is determined based on the stability of the anion. The strength of a base is determined based on the power to accept a proton.