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JEE Main 2025 Jan 28 Shift 1, Chemistry Q2: Principles Of Qualitative Analysis

JEE Main2025Jan 28, Shift 1Chemistry
Q.

Given below are two statements :

Statement I : In the oxalic acid vs KMnO (in the presence of dil HSO) titration the solution needs to be heated initially to 60°C, but no heating is required in Ferrous ammonium sulphate (FAS) vs KMnO titration (in the presence of dil HSO)

Statement II : In oxalic acid vs KMnO titration, the initial formation of MnSO takes place at high temperature, which then acts as catalyst for further reaction. In the case of FAS vs KMnO, heating oxidizes Fe into Fe by oxygen of air and error may be introduced in the experiment.

In the light of the above statements, choose the correct answer from the options given below :

  1. A

    Statement I is false but Statement II is true

  2. B

    Both Statement I and Statement II are true

  3. C

    Statement I is true but Statement II is false

  4. D

    Both Statement I and Statement II are false

Solution

The reaction of oxalate with permanganate in acidic medium is

At room temperature this reaction is sluggish, so the flask is warmed to about 60°C to get it started. Once a small amount of Mn forms, it autocatalyses further reaction, so heating is only needed initially. Statement I is correct on this count.

For the FAS versus KMnO titration, warming is avoided because atmospheric oxygen would oxidise Fe to Fe and introduce a positive error in the titre value. Statement II correctly explains both observations.

Both statements are true.

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