1. Some reactions involving iodine/iodide

2. Potassium iodide solution (right) is colourless. Here we are about to oxidise the iodide using orange bromine water. Oxidation of iodide

3. The orange colour of the bromine changes to the darker brown colour of iodine, I 2.

4. The brown colour of iodine in iodide is clearly seen in this beaker. Br 2 + 2e - → 2Br - 2I - → I 2 + 2e - Br 2 + 2I - → 2Br - + I 2 I 2 + I - → I 3 -

5. Reduction of iodine Iodine is a mild oxidising agent.

6. Colourless sodium thiosulfate solution will be used to reduce iodine to iodide.

7. As the thiosulfate solution is added, the brown colour begins to fade.

8. Almost all the iodine (I 2 ) has been reduced to iodide (I - ).

9. The final solution is completely colourless. I 2 + 2e - → 2I - 2S 2 O 3 2- → S 4 O 6 2- + 2e - I 2 + 2S 2 O 3 2- → 2I - + S 4 O 6 2-