Question

The conjugate acid of $H{S^ - }$ is.
A. ${S^{2 - }}$.
B. ${H_2}S$.
C. Both A and B.
D. None of the above.

Answer 1

Hint: We know that the Bronsted-Lowry theory of acid and base. According to this theory an acid is a proton donor while the base is a proton acceptor. The proton is represented by the symbol \[{H^ + }\] and we know that the conjugate acid is a cation and conjugate base is an anion.

Complete step by step answer: The Bronsted-Lowry theory is based on an acid and base reaction.
We know that, an acid is a species which has the capacity of donating a proton that is hydrogen ion is called Bronsted-Lowry acid and a base is species which has the capacity of accepting proton and a base it needs to have a lone pair of electrons on the base which bonds to the hydrogen ion.
Now, we see Conjugate acid.
According to Bronsted-Lowry theory the conjugate acid is the chemical species which is formed after the base accepts the hydrogen atom is called conjugate acid.
$Acid + Base \rightleftharpoons Conjugate\,Base + Conjugate\,Acid$
Apply the Bronsted-Lowry theory to find the conjugate acid$H{S^ - }$.
Hydrogen sulfuric acid dissociated into hydrogen sulfate ion. The conjugate acid of the hydrogen sulfate ion is the hydrogen sulfuric acid.
$H{S^ - }\left( {aq} \right) + {H_2}O\left( l \right) \rightleftharpoons {H_2}S\left( {aq} \right) + O{H^ - }\left( {aq} \right)$
In the above reaction $H{S^ - }$ acts as Bronsted-Lowry base which accepts hydrogen atom from its conjugate acid${H_2}S$.

So, the correct answer is “Option B”.

Note: We must know that a conjugate acid contains one hydrogen atom in addition and positive charge than the base from which is formed. A conjugate base has one hydrogen atom less and negative charge than the acid from which it is formed.
Example: Carbonic acid and hydronium ions are formed by the reaction of bicarbonate ions with the water.