Question

What is the conjugate base for ${{H}_{2}}S$?

Answer 1

Hint: This question is based on the theory of acids and bases by Bronsted-Lowry. This theory states that the species that donates a proton on the reaction is known as a conjugate acid. On the other hand, the species that accepts the proton donated by the conjugate acid is known as the conjugate base.

Complete answer:
Now, we know that a chemical compound is formed when the conjugate acid donates a proton to the conjugate base.
So, we can say that for an acid, its conjugate base is simply the parent acid minus one proton. When an acid is dissolved in water, the following reaction takes place
\[HA+{{H}_{2}}O\to {{H}_{3}}{{O}^{+}}+{{A}^{-}}\]
Where HA acts as the acid and ${{A}^{-}}$ acts as the conjugate base.
Similarly, for a base, its conjugate acid is simply the parent base plus one proton. When a base is dissolved in water, the following reaction takes place
\[{{A}^{-}}+{{H}_{2}}O\to HA+O{{H}^{-}}\]
Where ${{A}^{-}}$ acts as the base and HA acts as the conjugate acid.
Now, to find out the conjugate base of ${{H}_{2}}S$, let us see the reaction between the acid and water.
\[{{H}_{2}}S(aq)+{{H}_{2}}O(l)\to H{{S}^{-}}(aq)+{{H}_{3}}{{O}^{+}}(aq)\]
When hydrogen sulfide acid is dissolved in water, it dissociates into bisulfide anion and hydronium cation.
So, we can see that the conjugate base is a bisulfide ion $H{{S}^{-}}$.

Note:
It should be noted that the strength of a conjugate base or a conjugate acid depends on the strength of its parent acid or base. The stronger the parent acid or base, the weaker the conjugate base or acid that is formed.