Chemical amounts (A2)

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How do I find the percentage mass of iron (III) when reacting it with iodine followed by titrating the iodine with sodium thiosulphate?

Ulex says
I think what you may mean is that you would react the iron(III) solution with an excess of potassium iodide. The iron(III) ions react with the iodide ions to give iron(II) ions and iodine. The equation is
 
2Fe³⁺ + 2I^- -> 2 Fe²⁺ + I₂
 
Titrating this with sodium thiosulphate
 
I₂ + 2Na₂S₂O₃ -> 2NaI + Na₂S₄O₆
 
This means that every 1 mole of sodium thiosulphate used in the titration is equivalent to 1 mole of iron(III) ions in the original sample which should make it easy to work out the percentage of iron(III) in that sample.
 
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updated: 14 December 2006