Question

Explain why the stability of oxoacids of chlorine increases in the order given below:
$HClO<HCl{O}_2<HCl{O}_3<HCl{O}_4$

Answer 1

Stability of conjugate base

• When any acid releases a hydrogen ion, formation of its conjugate base takes place.
• More is the stability of the conjugate base, more will be the acidic strength of the corresponding acid.
• For oxoacids of chlorine, corresponding conjugate base are:

• Oxygen is more electronegative than chlorine thus, more the number of oxygen atoms bonded with the oxoacids, more will be the number of resonating structures due to which stability of the conjugate base will increase.
• The number of oxygen atoms bonded to 𝐶𝑙 are increasing from $HClOtoHCl{O}_4$, thus $Cl{O}_4^{-}$ will have the maximum number of resonating structures and will be most stable.

Resonating structures of $Cl{O}_2^{-}$


Resonating structures of $Cl{O}_3^{-}$


Resonating structures of $Cl{O}_4^{-}$

• Also, lower is the oxidizing power of acid, more will be its stability and among the oxoacids of chlorine, HClO has the highest oxidizing power due to less number of resonating structures thus it will be less stable.
• Thus stability of oxoanions will be: $Cl{O}^{-}<Cl{O}_2^{-}<Cl{O}_3^{-}<Cl{O}_4^{-}$
• Hence, $HCl{O}_4$ is the strongest acid but weaker oxidizing agent. Stability order of given oxoacids will be: $HClO<HCl{O}_2<HCl{O}_3<HCl{O}_4$