Sunday, July 3, 2022

When we titrate oxalic acid with a KMnO4 solution, it gets pink with the first drop of KMnO4 from the burette, why is that?

When we add the first drop of potassium permanganate (KMnO4) to a solution of oxalic acid (C2H2O4), the reaction happens, without a catalyst. So, you can see that the color is slowly disappearing.

Unless you shake it, the pink color gradually fades away if you shake the solution. Furthermore, once we add a few drops, the rate of disappearance accelerates, and as soon as we add a drop of KMnO4 the decolorization happens.

The reason for why it happens is given below.

When we add the first drop of potassium permanganate to a solution of oxalic acid (C2H2O4), the reaction happens automatically, i.e., uncatalyzed. So, we can observe that the color is slowly disappearing. 

After a few drops have been introduced, the formation of Mn2+ ion makes the reaction autocatalytic. KMnO4 droplets are now decolorized more rapidly than before.


What happens in the reaction between potassium permanganate and potassium oxalate?

In which a redox reaction is involved. Oxalic acid is oxidized to CO2 by KMnO4, which itself gets reduced to MnSO4. The reaction takes place in a medium that is acidic (sulphuric acid-H2SO4) and occurs between 60-70 °C.


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