A mixture of oxalic acid ( $H X_{2} C X_{2} O X_{4}$ , molar mass 90) and potassium hydrogen oxalate ( $KHC X_{2} O X_{4}$ , molar mass 128) is analysed. One portion needs 15.0 mL of 0.100 M NaOH for complete neutralisation. An equal portion needs 20.0 mL of 0.0200 M $KMnO X_{4}$ in hot acidic medium. The mass percentage of $KHC X_{2} O X_{4}$ in the mixture is:

Answer: B

Let the portion contain x mmol

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

and y mmol

KHC X_{2} O X_{4}

. Oxalate:

x + y = 20.0 \times 0.0200 \times 2.5 = 1.00

. Acid protons:

2 x + y = 15.0 \times 0.100 = 1.50

. So x = 0.50, y = 0.50. Masses: 45 mg and 64 mg. Percentage of

KHC X_{2} O X_{4}

= 64/109 x 100 = 58.7%.