Question

Choose the correct order of acidity order:

• A. $HClO<{HClO}_2$
• B. $H_2{SO}_4>H_2{SO}_3$
• C. $H_3{PO}_2<H_3{PO}_3$
• D. ${HNO}_3>{HNO}_2$
• E. $HF>HCl$
• F. $H_3{PO}_3>H_3{PO}_4$

Answer 1

Answer: (A), (B), (D), (F)

$HClO<{HClO}_2$
$H_2{SO}_4>H_2{SO}_3$
${HNO}_3>{HNO}_2$
$H_3{PO}_3>H_3{PO}_4$

The acidic character of oxyacids increases with increase in the oxidation state.

More is the number of $O$ atoms bonded, more electrons will be pulled away from $O-H$ bond, weaker will be the $O-H$ bond and stronger will be the acid. Hence, $HClO<HCl{O}_2$, $H_{2}S{O}_4>H_{2}S{O}_3$ and $HN{O}_3>HN{O}_2$

For options C and F, the correct order is $H_{3}P{O}_2<H_{3}P{O}_4<H_{3}P{O}_3$ because $H_{3}P{O}_3$ is polar.

The increase in the acidity is small as the number of unprotonated oxygen, responsible for the enhancement of acidity due to inductive effect remains the same. $HCl$ is more acidic than $HF$ due to strong $H-F$ bond (high bond dissociation enthalpy), high heat of dehydration for $HF$ due to an association in solution due to hydrogen bonding and low electron affinity of fluorine atom.