Follow the steps outlined below:
1. Accurately weigh out 0.90 g of KIO3 and make up to 250 ml of solution using
a volumetric flask.
2. Pipette 25.0 ml of the KIO3 solution into a clean conical flask. Add to this about
20 ml 1.0 M H2SO4 and about 10 ml of 0.5 M KI solution. This will liberate the iodine
(a brown solution).
IO3
-
(aq) + 6H+ (aq) + 5I-
(aq) → 3I2 (aq) + 3H2O (l)
3. Fill the burette with a 0.1 M Na2S2O3 solution. Titrate the iodine against the
thiosulfate solution until the solution becomes straw yellow.
4. At this point add about 1 ml soluble starch solution. The solution will now go blueblack.
Carry on titrating with dropwise additions of thiosulfate solution until the
solution just turns colourless. Note the final volume and calculate the titre.