[iyc]

There is a redox titration experiment using KMnO₄ as oxidizing agent.

The objective is to prepare an approximately 0.05M solution of oxalic dihyrate acid and use it to determine the concentration of a given KMnO₄.

there is a procedure that 25cm³ of a solution of oxalic acid, and add about 25cm³ of dilute H₂SO₄ and heat the mixture to about 60^oC.

I wanna ask what is the purpose of adding dilute sulphuric acid in a solution of oxalic acid? Can anyone tell me??

But I try first.
I think the oxalic acid in solution would decompose  into carbon dioxide and water in heating, so adding dilute sulphuric acid can provide a path of higher activation energy for decomposition or adding sulphuric acid can increase the strength of intermolecular forces between molecules in mixture so that the ethanidoate acid would not decompse easily in heating. Thus, it will not cause a decrease in number of mole of ethanidioate ion in heating and so for the latter redox titration.

[Borek]

Oxalic acid is pretty stable. You have to try harder

Think about permanganate end, not oxalic acid.

[iyc]

I think I have got a wrong way of thinking, so I try again.

As oxalic acid is a weak acid, so it ionize slightly to give hydrogen ion. Therefore, adding dilute sulphric acid can provide an acidic medium for MnO₄^- to react with ethanedioate ion.

I think it should be right. But let me ask a further question.
Why do we need to acidify the some oxidizing agent, e.g. MnO₄^-? Will MnO₄^- without acidifiying have oxidizing property??

[Borek]

Why do we need to acidify the some oxidizing agent, e.g. MnO₄^-? Will MnO₄^- without acidifiying have oxidizing property??

Write half-reaction for permanganate. Will addition of H⁺ move the equilibrium? In what pH will it be stronger oxidizer? The same hold for other oxidizers, like CrO4^2-.

In basic solutions permanganate gets reduced to MnO₂ only. You will not want to titrate solution full of brown precipitate, as it hides any color change at endpoint.

[Garneck]

In basic solutions permanganate gets reduced to MnO₂ only. You will not want to titrate solution full of brown precipitate, as it hides any color change at endpoint.

No, in a neutral solution you will get MnO₂. In a basic solution you will get MnO₄^2-.

[Borek]

OK, my bad. Still, low pH is needed for permanganate, not for oxalic acid.

[Garneck]

OK, my bad. Still, low pH is needed for permanganate, not for oxalic acid.

Yes, it is