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Why is the colour of chlorine water and potassium iodide solution brown?

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    Why is it brown
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    In the water you have Cl2 molecules and I- ions.

    Chloride ions are more stable than iodide ions, so we have

    Cl2(aq) + 2I-(aq) ---> I2(aq) + 2Cl-(aq)

    Halide ions are colourless in water, so the colour you see is the iodine. Iodine is brown in aqueous solution, hence you see brown.
 
 
 
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