Question

How would you identify the acid, base, conjugate acid and conjugate base in the following reaction:
$HCN + SO_4^{2 - } \to HSO_4^ - + C{N^ - }$

Answer 1

The definition of conjugate acid and bases pair is given by Bronsted and Lowry which is known as Bronsted – Lowry concept. According to Bronsted – Lowry acid reacts with the base and donates its proton to base and during this the acid becomes the conjugate base and the base becomes conjugate acid.

Complete step by step answer: The acids are defined as those species which release protons or contain hydrogen which it can donate to other substances.
The bases are defined as those species which accept the hydrogen ion released by the acids.
The acid and a base which differ from each other only by the presence or absence of protons are called conjugate acid-base pairs.
The acid reacts with base by donating its proton to the base. While doing this acid becomes the conjugate base. The formula of the conjugate base is the formula of the acid containing one hydrogen less. The reacting base becomes a conjugate acid. The formula of the conjugate acid is the formula of base with one extra hydrogen.
The given reaction is shown below.
$HCN + SO_4^{2 - } \to HSO_4^ - + C{N^ - }$
In this reaction, hydrogen cyanide reacts with sulphate ion to form hydrogen sulphate ion and cyanide ion.
In this reaction, hydrogen cyanide is an acid and cyanide anion is the conjugate base. Sulphate ion is the base and hydrogen sulphate ion is conjugate acid.

Note:
We also know that the conjugate base of sulphuric acid ${H_2}S{O_4}$ which is a very strong acid is hydrogen sulphate ion $HSO_4^{2 - }$ and the conjugate base of the anion $HSO_4^{2 - }$ is sulphate ion $SO_4^{2 - }$.