Question

if you take a table containing approximately 500 mg of ascorbic acid and disolve it in 31 ml of .4 M H2SO4, add 2.2 g of solid KI and 50.0 ml of .061 M KIO3 and then titrate it with 36 ml of .25 M Na2S2O3 the measured amount expressed in mg/tablet would be:

Answer 1

When iodate ions (IO3 ⁻) are added to an acidic solution containing iodide ions (I⁻), an oxidation-reduction reaction occurs:

Moles of IO₃^- = 0.061 x (50/1000) = 0.00305

Moles of H⁺ = 2 x 0.4 x (31/1000) = 0.0248

Moles of I^- = 2.2 / 166 = 0.012 (Limiting Reactant)

ascorbic acid + I₂ → 2 I⁻ + dehydroascorbic acid

Moles of I₂ formed = (3/5) x 0.012 = 0.0072 (limiting reactant)

Moles of S₂O₃^2- = 0.25 x (36/1000) = 0.009

Moles of Dehydroascorbic acid = 0.0072

Mass of dehydroascorbic acid = 0.0072 x 176.12 = 1.268 g