Question

In this experiment the concentration of Vitamin C/ascorbic acid is used to find the amount of iodine present through titration and the stoichiometric ratio. Furthermore, by finding the amount of iodine present before and after the equivalence point, the experiment presents us with the amount of iodine that reacts with the Vitamin C in “unknown B”.There were two titrations performed in this experiment, three times each. The first began with 50mL of Sodium Thiosulphate put in a burette. Approximately 2g of Potassium Iodide was stirred in a 250mL Erlenmeyer flask, with 10mL of 0.3M Sulphuric Acid, followed by 20mL of 1.0003x10-2M Potassium Iodate. The solution was initially a brown color, titrated until the solution becomes lighter. 1mL of starch indicator to the solution turned the lighter solution blue, and was titrated until the blue disappeared. The second titration began with 50mL of Sodium Thiosulphate in a burette. Placing approximately 2g of Potassium Iodide in a 250mL Erlenmeyer flask, 20mL of “Pink Drink”, with 10mL of 0.3M Sulphuric Acid, and 20mL of 1.0003x10-2M Potassium Iodate was stirred together. The brown mixture was titrated until it lightened; with 1mL of starch indicator added it changed to blue. The titration was carried out until the blue disappeared.

Using these equations
IO3 + 5I + 6H = 3I2 + 3H2O
I2 + 2S2O3 = 2I + S4O6

How do I go about finding the amount of vitamin C and iodine? I have equations but I'm told they're the wrong ones. Quite frankly I'm lost. This is the data I collected during the experiment.

	Titration 1(Na2SO3 mL)	Titration 2(Na2SO3 mL)	Titration 1(KI g)	Titration 2(KI g)
Trial 1	17.7	13.7	2.080	2.044
Trial 2	17.0	13.5	2.047	2.085
Trial 3	17.6	13.5	2.013	2.082
Avg	17.5	13.6	2.047	2.070

Answer 1

By using above process we cannot determine the amount of vitamin-c or ascorbic acid,Estimation of vitamin c is a redox titration,In presence of acid Potassium iodide and potassium iodate iodine is liberated and it reduces ascorbic acid to dehydro ascorbic acid,after complete conversion of ascorbic acid to dehydroascorbic acid free iodine combines with starch and blue colour will be formed,based on this principle we can find out the concentration of vitamin C.

Titration occurs in two steps,in first step Standardisation of Hypo by Std.Vitamin C,in second step we can estimate unknown vitamin C,

Generally 100ml of std.Vit.C contains 0.25g of vit.c,in titration we take 20ml so it contains 0.05g of vit.c,it consumes x ml hypo,unknown vit c consumes y ml hypo,.

So amount of vit c=y/x × 0.05,based on this we can determine vitamin c concentration.