Question

How many moles of 0.2 M KMnO4 were necessary to cause the color change to occur with the old H2O2 solution?

Answer 1

It's important to note that hydrogen peroxide solution is acidic. The following reaction will take place:

2 KMnO₄ + 3 H₂SO₄ + 5H₂O₂ = 2 MnSO₄ + K₂SO₄ + 5O₂ + 8H₂O

5 H₂O₂ + 2MnO₄^- + 6H⁺ = 5O₂ + 2Mn²⁺ + 8H₂O

If the volume of potassium permanganate solution was 0.1 L (or any other value), then number of moles must be:

$$n= M \cdot V = 0.2 \frac {moles}{L} \cdot 0.1 L = 0.02 moles$$

As the ratio hydrogen peroxide vs permanganate ion is 5:2, then moles of H₂O₂:

$$moles \space of \space H_2O_2 = \frac {5 \cdot 0.02}{2}= 0.05 \space moles$$