Question

Oxidising power of \[{\text{Cl}}{{\text{O}}^ - }{\text{, ClO}}_2^ - {\text{, ClO}}_3^ - {\text{, ClO}}_4^ - \] is:
A. \[{\text{ClO}}_4^ - {\text{ > ClO}}_2^ - > {\text{ClO}}_3^ - > {\text{Cl}}{{\text{O}}^ - }\]
B. \[{\text{ClO}}_2^ - > {\text{Cl}}{{\text{O}}^ - } > {\text{ClO}}_3^ - > {\text{ClO}}_4^ - \]
C. \[{\text{Cl}}{{\text{O}}^ - }{\text{ < ClO}}_2^ - {\text{ < ClO}}_3^ - {\text{ < ClO}}_4^ - \]
D. \[{\text{ClO}}_3^ - > {\text{ClO}}_2^ - > {\text{Cl}}{{\text{O}}^ - } > {\text{ClO}}_4^ - \]

Answer 1

Hint:First let us determine the factor that affects the oxidizing power of the oxyanions of chlorine. Also, then determine the change in the oxidation state of the central chlorine atom in these oxyanions of chlorine.

Complete step-by-step solution:
\[{\text{Cl}}{{\text{O}}^ - }{\text{, ClO}}_2^ - {\text{, ClO}}_3^ - {\text{, ClO}}_4^ - \] are conjugate bases of the oxyacids \[{\text{HClO, HCl}}{{\text{O}}_2}{\text{, HCl}}{{\text{O}}_3}{\text{, HCl}}{{\text{O}}_4}\]
The oxyacids \[{\text{HClO, HCl}}{{\text{O}}_2}{\text{, HCl}}{{\text{O}}_3}{\text{, HCl}}{{\text{O}}_4}\] are named as hypochlorous acid, chlorous acid, chloric acid and per chloric acid respectively.

The conjugate bases \[{\text{Cl}}{{\text{O}}^ - }{\text{, ClO}}_2^ - {\text{, ClO}}_3^ - {\text{, ClO}}_4^ - \] are named as hypochlorite ion, chlorite ion, chlorate ion and perchlorate ion respectively. The oxidation number of central chlorine atoms in hypochlorite ion, chlorite ion, chlorate ion and perchlorate ion is +1,+3,+5 and +7 respectively. With increase in the oxidation number of the chlorine atom, the oxidizing power of the conjugate bases of the oxyacids increases. This is because with increase in the oxidation number of the central chlorine atom, the affinity for the electrons of the other species increases and the oxyanion can more readily accept electrons from the other species.

The increasing order of the oxidizing power of conjugate bases of oxyacids of chlorine is \[{\text{Cl}}{{\text{O}}^ - }{\text{ < ClO}}_2^ - {\text{ < ClO}}_3^ - {\text{ < ClO}}_4^ - \]

Hence, the correct answer is the option (C).

Note: In a redox reaction, one species is oxidized whereas other species is reduced. The species that is oxidized is called the reducing agent and the species that is reduced is called oxidizing agent. Increase in the oxidation number is the oxidation whereas decrease in the oxidation number is the reduction.