Question

Which of the following represent a conjugate acid/base pair?
A. ${{\text{H}}_{\text{3}}}{{\text{O}}^{\text{ + }}}{\text{/}}{{\text{H}}_{\text{2}}}{\text{O}}$
B. ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{/SO}}_{\text{4}}^{{\text{2 - }}}$
C. ${\text{HCO}}_{\text{3}}^{\text{ - }}{\text{/CO}}_{\text{3}}^{{\text{2 - }}}$
D. All are conjugate acid base pairs

Answer 1

The acid / base pairs which differ by a proton are called conjugate acid / base pairs.
OR
The base that is formed by donation of a proton from an acid is called the conjugate base of that acid. The acid that is formed by accepting a proton from a base is called conjugate acid of that base

Complete step by step solution:
In acids and bases proton-transfer processes are broken into two hypothetical steps: (1) donation of a proton by an acid, and (2) acceptance of a proton by a base . The steps are useful because they make it easy to see what species is left after an acid donates a proton and what species is formed when a base accepts a proton. We shall use hypothetical steps or half-equations in this section, but free protons never actually exist in aqueous solution
Protonium ion and water differ by a proton and hence, they are conjugate acid base pair
Sulphuric acid and sulphate ions differ by two protons. Conjugate base of sulphuric acid is bisulphate ion. Conjugate base of bisulphate ion is sulphate ion
Bicarbonate ions and carbonate ions differ by a proton. Hence, they are conjugate acid base pairs.

**Hence, options A and C are correct.

Note: **
Whenever an acid donates a proton, the acid changes into a base, and whenever a base accepts a proton, an acid is formed. An acid and a base which differ only by the presence or absence of a proton are called a conjugate acid-base pair. Thus ${\text{N}}{{\text{H}}_{\text{3}}}$ is called the conjugate base of ${\text{NH}}_{\text{4}}^{\text{+}}$, and ${\text{NH}}_{\text{4}}^{\text{+}}$ is the conjugate acid of ${\text{N}}{{\text{H}}_{\text{3}}}$. Similarly, ${\text{HF}}$ is the conjugate acid of ${{\text{F}}^{\text{-}}}$, and ${{\text{F}}^{\text{-}}}$ the conjugate base of ${\text{HF}}$ .