15.0 mL of an iodine solution of unknown molarity was titrated against a .001 M solution of S2o32-. The blue black iodine-starch complex just disappeared when 20.2 mL of thiosulfate was added. What is the exact molarity of the Ia solution

Answer 1

I2 + 2S2O3^2- ==> S4O6^2- + 2I^-

mols S2O3^2- = M x L = ?
Convert mols S2O3^- to mols I2 using the coefficients in the balanced equation.
Then M S2O3^2- = mols S2O3^2-/L S2O3^2-