Question

${Cl}^{-}$ ion is the conjugate base of:
a) $HCl$
b) $HOCl$
c) $HCl{O}_{3}$
d) $HCl{O}_{4}$

Answer 1

Hint: When an acid donates a proton, then what is left behind is known as its conjugate base. It has one less hydrogen ion and one more $^{-}$ charge that the corresponding acid.

Complete step by step answer: The conjugate base is the compound that is formed after when the acid donates a proton. More generally, it can be defined as the base member, ${Y}^{-}$, of a pair of compounds that transforms into each other by gaining or losing a proton. It can gain a proton during a chemical reaction.

- The strength of a conjugate base can be seen as its ability to pull hydrogen protons towards itself.

- A strong conjugate base is the one which can hold on to the hydrogen proton when in solution and acid will not dissociate.

- A strong acid gives a weak conjugate base and a weak acid will give a strong conjugate base.

In the question given, ${Cl}^{-}$ is the conjugate base of the strong acid $HCl$. $HCl$ dissolves in water to give ${H}^{+}$ ion and ${Cl}^{-}$ ion.

$HCl\quad \longrightarrow \quad { H }^{ + }\quad +\quad { Cl }^{ - }$.

${Cl}^{-}$ has an extra electron which it can donate to stabilize itself. So, it is a conjugate base.

Hence, the correct option is (a).

Note: There is a difference between a base and a conjugate base. A conjugate base is a type of base which is formed when an acid loses a proton. Whereas, a base is a chemical species that donates electrons and accepts protons or is capable of releasing ${OH}^{-}$ ions in aqueous solution.