Question

Assign reason for the following:
(i) $H_{3}P{O}_2$ is a stronger reducing agent than $H_{3}P{O}_4$.
(ii) Sulphur shows more tendency for catenation than Oxygen.
(iii) Reducing character increases from $HF$ to $HI$.

Answer 1

(i) Due to pressure on P - H bond, $H_{3}P{O}_2$ is a stronger reducing agent than $H_{3}P{O}_4$ which does not have P - H bond.
(ii) Due to the small size, the lone pairs on the O atoms repel the bond pair of the O - O bond to a greater extent that the lone pairs of electrons on the S atom in S - S bond. As a result, S - S bond is stronger than O - O bond.
(iii) Since the bond dissociation enthalpy of $H-X$ bond increases from $H-F$ to $H-I$ as the size of atom increases from F to I. Therefore, the reducing character increases from $HF$ to $HI$.