Question

What is the conjugate base of $H{S^ - }$?

Answer 1

When an acid dissociates its ions in water, it loses a hydrogen. The species that is formed due to this dissociation is the acid’s conjugate base. In general, a conjugate base is the base member (${X^ - }$) of a pair of compounds that transform into each other by gaining or losing a proton in a chemical reaction. The proton or hydrogen is donated by the conjugate acid.

Complete answer:
We can recognize a conjugate acid or base of a compound by figuring out the cation and anion of the given compound. The conjugate acid of a compound is the cationic part and conjugate base is the anionic part of the compound.
In the question, we are given $H{S^ - }$ as the compound. Here, we can easily figure out the conjugate base by noticing the charge present in the compound. Since we have a negative charge on$S$, so we can say that this is the anionic part of the compound as well as the conjugate base.
Therefore, the conjugate base of $H{S^ - }$ is ${S^ - }$.

Note:
Conjugate acids and bases are a part of Brownsted-Lowry theory of acids and bases. According to this theory, the species that donates hydrogen or proton in a reaction is the conjugate acid. While the one that accepts the hydrogen or proton in a reaction is the conjugate base.
The general chemical reaction of an acid-base reaction is:
$Acid + Base \rightleftharpoons Conjugate{\text{ }}Base + Conjugate{\text{ }}Acid$