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Witness iodine/iodide reactions as iodide is oxidized to iodine by bromine water, turning from orange to brown, and then reduced back to iodide by sodium thiosulfate, resulting in a colorless solution. Explore the chemical transformations in a beaker.
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Oxidation of iodide Potassium iodide solution (right) is colourless. Here we are about to oxidise the iodide using orange bromine water.
The orange colour of the bromine changes to the darker brown colour of iodine, I2.
The brown colour of iodine in iodide is clearly seen in this beaker. Br2 + 2e- → 2Br- 2I- → I2 + 2e- Br2 + 2I- → 2Br- + I2 I2 + I- → I3-
Reduction of iodine Iodine is a mild oxidising agent.
Colourless sodium thiosulfate solution will be used to reduce iodine to iodide.
As the thiosulfate solution is added, the brown colour begins to fade.
The final solution is completely colourless. I2 + 2e-→ 2I- 2S2O32- → S4O62- + 2e- I2 + 2S2O32- → 2I- + S4O62-