Question

Which of the following acids are added in the titration of oxalic acid and potassium permanganate?
(A) $HN{O_3}$
(B) $HCl$
(C) $C{H_3}COOH$
(D) ${H_2}S{O_4}$

Answer 1

In order to find which of the following acids are added in the titration between the oxalic acid and potassium permanganate, we must know what type of reaction is taking place. This reaction is an example for the redox titration.

Complete answer:
The titration of potassium permanganate with the oxalic acid is an example of Redox titration. Redox reaction involves the oxidation of one species and the reduction of the other species. The oxalic acid which is the analyte will act as the reducing agent. While the potassium permanganate is the titrant is a very good oxidising agent. Potassium permanganate can work strongly only when it is present in the acidic medium than in the alkaline medium. Therefore, we are adding sulphuric acid in order to maintain the acidic medium. The oxidising action of potassium permanganate in the acidic medium is given below:
$Mn{O_4} + 8{H^ + } + 5{e^ - } \to M{n^{2 + }} + 4{H_2}O$
In the redox reaction between the potassium permanganate and oxalic acid, potassium permanganate will act as the self-indicator.
The reaction is given
$2MnO_4^ - + 5{C_2}O_4^2 + 16{H^ + } \to 2M{n^{2 + }} + 10C{O_2} + 8{H_2}O$
The end point is the appearance of pale permanent pink colour from the colourless solution. This pale permanent pink colour is obtained due to the presence of excess of unreacted potassium permanganate.

Therefore, the correct answer is the option (D).

Note:
We must follow certain precautions while carrying out the above given redox reaction. They are:
- Clean all the apparatus with the distilled water.
- We have to thoroughly rinse the burette and pipette.
- We have to take accurate readings.
- We have to avoid using corked burette as potassium permanganate can affect it.
- We have to take upper meniscus as the potassium permanganate is dark in colour.