how do you Convert moles S2O3^-2 to moles I2

Answer 1

I have a feeling this is not the question you really want answered. I think I remember you asking about titration of Cu with S2O3. However, to answer your question:
2S2O3^-2 + I2 ==> 2I^- + S4O6^-2
Use the coefficients in the balanced equation to convert moles of one material to moles of another.
Let's say we have 0.5 M S2O3^-2 and we used 20 mL, then moles S2O3^-2 = M x L = 0.5M x 0.02L = 0.01 moles. Now to convert that to moles I2, we use
0.01 moles S2O3^-2 x (1 mole I2/2 moles S2O3^-2) = 0.01 x (1/2) = 0.005 moles I2.