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

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

2S2O32- → S4O62- +2e- I2 → I-

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.

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

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

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 0.2000 mol/dm3 solution of thiosulfate. 29.45cm3 of thiosulfate was needed. Calculate concentration of Chlorate(I) ions in solution.