Answer to Question #98428 in General Chemistry for Mario

Question

What will happen to the normality of the potassium permanganate if we store it in a transparent bottle for several days? Explain your answer.
How would this action affect the calculated value of the normality of the unknown oxalate solution? Explain

Answer 1

Q98428

Solution:

Potassium permanganate ($KMnO_4$ ) is stored in dark bottles because to not exposed to light, If it exposed to light it will start decomposing. Small amount of light can provide enough energy for the permanganate to oxidise water.

Thus, if the chemical is stored in transparent bottles, which effectively means exposing it to sunlight; it decomposes acording to the reaction:

$4MnO_4^-+2H_2O\to 4MnO_2(s)+3O_2+4OH^-$

The solid $MnO_2$ formed catalyses the auto-decomposition thus decreasing the permanganate ion concentration.

$\therefore$ The normality of the potassium permanganate decreases if we store it in a transparent bottle for several days.

Also, this would affect the calculated value of molarity of the unknown oxalate solution in the sense as to giving false results.

If the unknown oxalate solution would be titrated with freshly prepared potassium permanganate it would give a greater molarity as compared to the molarity obtained on titrating the same unknown oxalate solution with a potassium permanganate solution which was stored in a transparent bottle for several days.