An aliquot contains H2C2O4 and NaHC2O4 only. It needs 42.0 mL of 0.150 N NaOH for complete neutralisation and, in a separate identical aliquot, 45.0 mL of 0.200 N KMnO4 (acidic medium) for complete oxidation. Calculate the mass of NaHC2O4 (molar mass 112 g mol^-1) in the aliquot, in mg (nearest integer).

JEE Advanced levelNumerical answerDifficulty 3 of 3eq052

An aliquot contains $H X_{2} C X_{2} O X_{4}$ and $NaHC X_{2} O X_{4}$ only. It needs $42.0 mL$ of $0.150 N$ $NaOH$ for complete neutralisation and, in a separate identical aliquot, $45.0 mL$ of $0.200 N$ $KMnO X_{4}$ (acidic medium) for complete oxidation. Calculate the mass of $NaHC X_{2} O X_{4}$ (molar mass $112 g mo l^{- 1}$ ) in the aliquot, in mg (nearest integer).

Numerical answer type, answer in mg, tolerance 0.5.

Let

a

and

b

be mmol of

H X_{2} C X_{2} O X_{4}

and

NaHC X_{2} O X_{4}

. Neutralisation:

2 a + b = 0.150 \times 42.0 = 6.3

meq. Oxidation (each has

n = 2

2 a + 2 b = 0.200 \times 45.0 = 9.0

meq. Subtracting the first from the second gives

b = 2.7

mmol, and then

a = (6.3 - 2.7) /2 = 1.8

mmol. Mass of

NaHC X_{2} O X_{4} = 2.7 \times 112 = 302.4 mg