Equilibrium law
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I am doing an investigation on partition coefficient of iodine in water and hexane. I don't understand some of the procedures on the notesheet I was given. Why is it necessary to add H2SO4 into the mixture at the very beginning? Why is it necessary to add KI(aq) into the hexane layer before doing titration with thiosulphate?
Ulex replies
This is a bit tricky to answer when I haven’t seen the instruction sheet! I can’t immediately see a reason for using acid – in fact, if you are titrating with sodium thiosulphate I can see a very good reason for not having any acid present.
The reason for adding KI is a bit more reasonable. If you are titrating the hexane layer (or a sample of it), the aqueous sodium thiosulphate will not mix with it. If you add some KI(aq), this will extract the iodine into an aqueous layer so that it can more easily react with sodium thiosulphate.
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updated: 20 December 2006
