Work out a general equation for finding the I₂ # from your titration data. Remember that you are titrating the amount of I₂ LEFT OVER. Let "B" stand for the ml of 1 M S₂O₃^-2 used in the blank titration, S for the ml of 1 M S₂O₃^-2 used in the sample titration and W for the weight of the sample.

the balanced rxn in the titrations: I₂ + 2 S₂O₃^-2 --------> 2 I^- + S₄O₆^-2

this might help:

a. Write a general expression for the grams of I₂ in the blank using the volume of the 1 M S₂O₃^-2 used in the blank titration, B.

b. Write a general expression for the grams of I₂ left over from an oil or fat sample using the volume of the 1 M S₂O₃^-2 used in the sample titration, S.

c. Combine your expressions from a. and b. above to create an expression for the grams I₂ used by the sample. Algebraically simplify what you come up with.

d. Now write an expression for the grams I₂ used per gram of oil or fat by including the weight of the sample, W in your equation.

e. Multiply your expression in d. by 100 to find I₂ #, the grams of I₂ used per 100 g of oil or fat.