Amount of oxalic acid present in a solution can be determined by its titration with $\mathrm{KMnO}_{4}$ solution in the presence of $\mathrm{H}_{2} \mathrm{SO}_{4}$. The titration gives unsatisfactory result when carried out in the presence of HCl, because HCl

(C) reduces permanganate to $\mathrm{Mn}^{2+}$

(A) gets oxidised by oxalic acid to chlorine

(B) furnishes $\mathrm{H}^{+}$ ions in addition to those from oxalic acid

(D) oxidises oxalic acid to carbon dioxide and water

JEE Main · 2008 · 27 Apr 2008 · Offline · Practical and Analytical Chemistry

Amount of oxalic acid present in a solution can be determined by its titration with

KMnO_{4}

solution in the presence of

H_{2} SO_{4}

. The titration gives unsatisfactory result when carried out in the presence of HCl, because HCl

(A)gets oxidised by oxalic acid to chlorine
(B)furnishes $H^{+}$ ions in addition to those from oxalic acid
(C)reduces permanganate to $Mn^{2 +}$ ✓ Correct
(D)oxidises oxalic acid to carbon dioxide and water

Answer: (C)

Solution

Permanganate titrations of oxalic acid are run in sulphuric acid because hydrochloric acid interferes: the chloride ion is itself oxidised by permanganate, so some of the permanganate is spent on chloride rather than on the oxalic acid being estimated. In effect the hydrochloric acid reduces the permanganate to

M n^{2 +}

, consuming titrant and spoiling the end point, which is why the result is unsatisfactory.

JEE Main · 2008 · 27 Apr 2008 · Offline · Single correct option

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JEE Main · 2008 · 27 Apr 2008 · Offline · Practical and Analytical Chemistry

Solution

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