Iodimetric Titration of Vitamin C By: Mohammad Mashal

Directions: Dissolve two tablets in 60 mL of 0.3 M H2SO4. Add 2 g of solid KI and 50.00 mL of standard KIO3.

60 mL 0.3 M H2SO4. 2 g of KI. 50.00 mL of standard KIO3. I2 + I(-1) I(-1)3

Then titrate with standard thiosulfate until the solution has a (pale blue) color. I(-1) 3 + 2S2O(-2) 3  3I(-1) + Tetrathionate

While Titration Add 2 mL of starch indicator just before the end point.

Q: why we using back titration in this experiment ?

A: because the end point is clearer than the end point of the direct titration.