Question

Calculate the volume required for equivalence point when titrating 500 mg of ascorbic acid with 0.0400 M IO3- solution in the presence of excess iodide

Answer 1

IO₃^- (aq) + 6 H+ (aq) + 5 I^- (aq) -> 3 I₂ (aq) + 3 H2O

one mole IO₃^- produce 3 mole I₂.

The iodine formed will react with the ascorbic acid.
C6H8O6 + I₂ -> C6H6O6 + 2 I^- (aq) + 2 H⁺ (aq)

in this reaction one mole ascorbic acid react with one mole I₂.

500 mg of ascorbic acid = mass / molar mass = 0.500 / 176.12 = 2.839 * 10^-3 mole.

in the first reaction  2.839 * 10^-3 mole I2 produced.

so moles of IO₃^- = 2.839 * 10^-3 / 3 = 9.46 * 10^-4 mole.

volume required of IO₃^- = 1000 * 9.46 * 10^-4 / 0.0400 = 23.65 ml. (answer)