Oxalic acid is a reducing agent and hence, reduces a solution of potassium permanganate causing discoloration of the solution. The relevant chemical equation can be written as:
`2MnO_4^(-) + 5C_2H_2O_4 + 6H_3O^+ -> 2Mn^(2+) + 10CO_2 + 14H_2O`
Here, manganese reduces from +7 state to +2 oxidation state. The potassium permanganate solution is purple in color and when a sufficient quantity of oxalic acid is added, the solution loses the color and gets decolorized.
One easy way to observe it at home or in school is to use a rhubarb plant. Rhubarb sticks contain oxalic acid and can be used to demonstrate this chemical reaction. Simply add small pieces of rhubarb sticks to potassium permanganate solution and you will see it getting decolorized. This simple experiment can also be used to demonstrate how the surface area of rhubarb sticks affects the rate of reaction. The higher the surface area, the faster the discoloration of the potassium permanganate solution.
Hope this helps.
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