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    I did a titration to find the concentration of household bleach with known sodium thiosulphate.

    We had to add sulfuric acid and potassium iodide to the bleach first to get the purple colour from I2 molecules.

    OCl- + 2I- + H+ -> Cl- + H20 + I2

    and then titrate against sodium thiosulfate to a colourless endpoint.

    I2 + 2Na2S2O3 -> 2NaI + Na2S4O6

    The question is why should you add the potassium iodide to the bleach before the sulfuric acid?

    Thanks for anyone who can help me with this
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Updated: November 16, 2008


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