Question

Which of the following is the strongest oxidising agent?

• A. HCIO
• B. HCIO2
• C. HCIO3
• D. HCIO4

Answer 1

Answer: (A)

HCIO

Answer 2

To determine the strongest oxidizing agent among the given oxyacids of chlorine (HClO, HClO2, HClO3, HClO4), we first determine the oxidation state of chlorine in each compound:

1. HClO (Hypochlorous acid):
   Let the oxidation state of Cl be $x$.
   $1 + x + (-2) = 0 \implies x = +1$

2. HClO2 (Chlorous acid):
   Let the oxidation state of Cl be $x$.
   $1 + x + 2(-2) = 0 \implies 1 + x - 4 = 0 \implies x = +3$

3. HClO3 (Chloric acid):
   Let the oxidation state of Cl be $x$.
   $1 + x + 3(-2) = 0 \implies 1 + x - 6 = 0 \implies x = +5$

4. HClO4 (Perchloric acid):
   Let the oxidation state of Cl be $x$.
   $1 + x + 4(-2) = 0 \implies 1 + x - 8 = 0 \implies x = +7$

An oxidizing agent is a substance that oxidizes other substances by getting itself reduced (gaining electrons). The strength of an oxidizing agent is related to its tendency to be reduced.

For oxyacids of the same element, the general trend for oxidizing power is that it decreases as the oxidation state of the central atom increases. This might seem counter-intuitive at first, as a higher oxidation state implies a greater electron deficiency. However, the stability of the higher oxidation state plays a crucial role.

• HClO (+1 oxidation state): This is the least stable of the oxyacids and readily decomposes to release nascent oxygen, which is a very powerful oxidizing agent. Its high reduction potential (e.g., HClO + H$^+$ + 2e$^-$ $\rightarrow$ Cl$^-$ + H2O, E° = +1.49 V) indicates its strong oxidizing nature.
• HClO4 (+7 oxidation state): This is the most stable oxyacid of chlorine due to the high electronegativity of oxygen atoms and extensive charge delocalization. While it is a very strong acid, its oxidizing power is significant only under harsh conditions (hot and concentrated). In dilute solutions at room temperature, it is a relatively weak oxidizing agent because the highly stable +7 oxidation state is resistant to reduction.

The general order of oxidizing strength for chlorine oxyacids is:
HClO > HClO2 > HClO3 > HClO4

This is because, as the number of oxygen atoms increases (and thus the oxidation state of chlorine increases), the stability of the oxyacid increases, making it less reactive as an oxidizing agent under normal conditions.

Therefore, HClO (hypochlorous acid) is the strongest oxidizing agent among the given options.