✔ 最佳答案
Method 1 : Balancing the charges
MnO₄⁻ + 8H⁺ → Mn²⁺ + 4H₂O
When electrons have not yet been added to the equation :
Total charges on the left = (-1) + 8 × (+1) = +7
Total charges on the right = +2
To make the charges are equal on the both side, 5e⁻ should be added to the left, i.e.
MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O
Method 2 : By the change in oxidation number
MnO₄⁻ + 8H⁺ → Mn²⁺ + 4H₂O
Oxidation number of Mn on the left (in MnO₄⁻) = +7
Oxidation number of Mn on the right (in Mn²⁺) = +2
Decrease in oxidation number = 5
To decrease the oxidation number by 5, 5e⁻ should be added to the reactant side, i.e.
MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O