Question

The $p{K}_a$ of oxoacids of chlorine in water follows the order:

• A. $HClO<HCl{O}_3<HCl{O}_2<HCl{O}_4$
• B. $HCl{O}_4<HCl{O}_3<HCl{O}_2<HClO$
• C. $HCl{O}_4<HCl{O}_2<HCl{O}_3<HClO$
• D. $HCl{O}_2<HClO<HCl{O}_3<HCl{O}_4$

Answer 1

Answer: (B)

$HCl{O}_4<HCl{O}_3<HCl{O}_2<HClO$

The higher the oxidation number of chlorine, higher is the acidic strength of the oxoacid of chlorine. $HCl{O}_4$ has the highest number of oxygen atoms, hence the oxidation number of chlorine is highest in it. Therefore, it is the most acidic. Therefore, it has the smallest value of $p{K}_{\alpha }$. Similarly, the oxidation number of chlorine in $HClO$ is the lowest because it has the least number of oxygen atoms. Hence its acidic strength is the least, and so its $p{K}_{\alpha }$ is the highest.