‘M’ is the molecular weight of KMnO₄. The equivalent weight of KMnO₄ when it reacts according to the equation 2KMnO₄ + 3H₂SO₄ + 5H₂C₂O₄ → K₂SO₄ + 2MnSO₄ + 8H₂O + 10CO₂

The equivalent weight of KMnO₄ is calculated based on its molecular weight and the valency factor associated with the redox reaction it undergoes. In this reaction, potassium permanganate (KMnO4) reacts with oxalic acid (H₂C₂O₄) in the presence of sulfuric acid (H₂SO₄). The reaction is as follows:

2KMnO₄ + 3H₂SO₄ + 5H₂C₂O₄ → K₂SO₄ + 2MnSO₄ + 8H₂O + 10CO₂    

The key to finding the equivalent weight of KMnO4 is understanding how the oxidation state of manganese (Mn) changes in the reaction. In KMnO₄, manganese has an oxidation state of +7. During the reaction, manganese is reduced to an oxidation state of +2 in MnSO₄. This change in oxidation state helps us determine the valency factor, which is crucial for calculating the equivalent weight of KMnO₄.

Step-by-Step Calculation

1. Identify the molecular weight of KMnO4: The molecular weight of KMnO₄ is represented as 'M'.
2. Oxidation State Change: The oxidation state of manganese changes from +7 to +2. The change in oxidation state is calculated as:
   • Initial oxidation state of Mn: +7
   • Final oxidation state of Mn: +2
   • Oxidation state change: +7 - (+2) = 5
3. Determine the valency factor: The valency factor is the number of electrons transferred in the reaction. In this case, the valency factor is 5 because the manganese ion undergoes a change of 5 in oxidation state.
4. Calculate the equivalent weight: The equivalent weight of KMnO₄ is given by the formula: 
   Equivalent weight = M / Valency factor 
   Since the valency factor is 5, the equivalent weight of KMnO₄ is M/5.

Conclusion

The equivalent weight of KMnO₄ is calculated by dividing its molar mass (M) by the valency factor, which is 5 in this case. Therefore, the equivalent weight of KMnO₄ is M/5.

In summary, understanding the reaction and the change in oxidation state of manganese is crucial for calculating the equivalent weight of KMnO₄. The equivalent weight of KMnO₄ is essential for stoichiometric calculations in redox reactions involving this compound.