3. Redox titrations – iodine and thiosulfate
L.O.:
Understand how to carry out redox titrations and carry out structured calculations involving MnO4- and I2/S2O32-

4. 2S2O32- → S4O62- +2e-
I2 → I-

5. Using iodine and thiosulfate to find out the concentration of an unknown OXIDISING agent
Iodine is reduced by thiosulfate ions into iodide ions in this reaction 2S2O32- (aq) + I2 (aq)  2I- (aq) + S4O62-(aq) A small amount of starch can be added to help identify the end point. Starch-iodine complex is dark/black.

6. Uses of the iodine/thiosulfate redox reaction
Iodide ions are added to an oxidising agent which oxidises them into iodine
You work out concentration of iodine by titrating the solution against a known number of moles of thiosulphate ions

7. Work out the balanced equation for the oxidation of Iodide by bleach (ClO-)

8. 30. 00 cm3 of bleach was added to an excess of iodide ions
30.00 cm3 of bleach was added to an excess of iodide ions. The iodine formed was titrated against mol/dm3 solution of thiosulfate cm3 of thiosulfate was needed. Calculate concentration of Chlorate(I) ions in solution.