Question

What is meant by the conjugate acid-base pair? Find the conjugate acid/base for the following species.
$HN{{O}_{2}},C{{N}^{-}},HCl{{O}_{4}},{{F}^{-}},O{{H}^{-}},CO_{3}^{2-}\text{ and }{{S}^{2-}}$ .

Answer 1

. A pair of compounds is said to be the conjugate acid base pair if they differ by a proton. Add a proton to get the conjugate acid of a compound and remove a proton to obtain the conjugate base of the respective compound.

Complete step by step answer:
Given compounds are
$HN{{O}_{2}},C{{N}^{-}},HCl{{O}_{4}},{{F}^{-}},O{{H}^{-}},CO_{3}^{2-}\text{ and }{{S}^{2-}}$
We know that an acid base pair is differ by a proton, so the conjugate acid base pair of the compound
$HN{{O}_{2}}$Is $NO_{2}^{-}$ which differ by a proton or ${{H}^{+}}$ ion forms a conjugate acid base pair.

- $C{{N}^{-}}$ Forms the conjugate acid base pair when it accepts a proton forming $HCN$ and hence the conjugate acid base pair of $C{{N}^{-}}$ is $HCN$.
- $HCl{{O}_{4}}$ Forms the conjugate acid base pair when it donates a proton forming $ClO_{4}^{-}$ and hence the conjugate acid base pair of $HCl{{O}_{4}}$ is $ClO_{4}^{-}$.
- ${{F}^{-}}$ Forms the conjugate acid base pair when it accepts a proton forming $HF$and hence the conjugate acid base pair of ${{F}^{-}}$ is $HF$.
- $O{{H}^{-}}$ Forms the conjugate acid base pair when it accepts a proton forming ${{H}_{2}}O$ and hence the conjugate acid base pair of $O{{H}^{-}}$ is ${{H}_{2}}O$ it can also donate a proton forming ${{O}^{2-}}$ also a conjugate acid base pair of $O{{H}^{-}}$.
- $CO_{3}^{2-}$ Forms the conjugate acid base pair when it accepts a proton forming $HCO_{3}^{-}$ and hence the conjugate acid base pair of $CO_{3}^{2-}$ is $HCO_{3}^{-}$.
- ${{S}^{2-}}$ Forms the conjugate acid base pair when it accepts a proton forming $H{{S}^{-}}$ and hence the conjugate acid base pair of ${{S}^{2-}}$ is $H{{S}^{-}}$.

Note: An acid or a base can form a conjugate acid base pair either by accepting a proton or by donating a proton which differs by a proton forming a conjugate acid base pair. Sometimes a compound can act as both, either conjugate acid or conjugate base by accepting or donating a proton.