Maximum Change in Oxidation Number during the Reaction between Potassium Chlorate, Oxalic Acid, and Sulphuric Acid

When a mixture of potassium chlorate (KClO3), oxalic acid (H2C2O4), and sulfuric acid (H2SO4) is heated, a redox reaction takes place. In this reaction, the oxidation numbers of various elements involved change. Let's analyze the oxidation number changes for each element in the reaction:

Potassium (K):
- In KClO3, the oxidation number of potassium (K) is +1.
- In the products, KClO3 decomposes into KCl and O2 gas. The oxidation number of potassium remains +1 throughout the reaction as it is not directly involved in any redox changes.

Chlorine (Cl):
- In KClO3, the oxidation number of chlorine (Cl) is +5.
- In the products, chlorine undergoes a reduction and its oxidation number decreases to -1 in KCl.

Oxygen (O):
- In KClO3, the oxidation number of oxygen (O) is -2.
- In the products, oxygen is released as O2 gas, and its oxidation number remains -2 throughout the reaction.

Carbon (C):
- In oxalic acid (H2C2O4), the oxidation number of carbon (C) is +3.
- In the products, carbon undergoes an oxidation and its oxidation number increases to +4 in CO2 gas.

Hydrogen (H):
- In oxalic acid (H2C2O4) and sulfuric acid (H2SO4), the oxidation number of hydrogen (H) is +1.
- In the products, the oxidation number of hydrogen remains +1 throughout the reaction.

Sulfur (S):
- In sulfuric acid (H2SO4), the oxidation number of sulfur (S) is +6.
- In the products, sulfur undergoes a reduction and its oxidation number decreases to +4 in SO2 gas.

Analysis:
- From the above analysis, it is evident that the element undergoing the maximum change in oxidation number during the reaction is chlorine (Cl).
- Chlorine goes from an oxidation number of +5 in potassium chlorate (KClO3) to -1 in potassium chloride (KCl), resulting in a change of 6 oxidation units.
- This change indicates that chlorine is being reduced during the reaction.

Summary:
- The element undergoing the maximum change in oxidation number during the reaction between potassium chlorate, oxalic acid, and sulfuric acid is chlorine (Cl).
- Chlorine starts with an oxidation number of +5 and ends with an oxidation number of -1, resulting in a change of 6 oxidation units.
- This change indicates the reduction of chlorine during the reaction.