Group 7: Halogens
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I am currently working on experiment 6.8 in the Nuffield course (preparation and purity of potassium iodate and potassium iodide) as a practice practical. Please could you give me an outline of what this experiment is about, as I don’t really understand what we are doing and what we are trying to find.
Ulex says
The first point of the experiment is to make a sample of potassium iodate(V), KIO3. This is a compound you probably won’t have come across before and is a good illustration of the fact that the halogens do not always have an oxidation number of –1 in their compounds.
The snag is that the method chosen for making this compound produces not only KIO3 but rather a lot of potassium iodide at the same time.
Fortunately it is possible to use a cunning trick based on differences of solubility to separate the KIO3 from the KI.
You now have samples of the two compounds.
The second point of the experiment is to learn an important analytical reaction, the titration of iodine solution with sodium thiosulphate solution. Until now, you may have thought that all titrations involved acids and alkalis. In this reaction, redox is involved instead.
The third point of the experiment joins the other two points together. You use the iodine-thiosulphate titration to find out how successful you were in separating potassium iodate(V) from potassium iodide on the assumption that your sample of potassium iodate(V) is likely to have some potassium iodide in it and vice versa.
Always carry out a risk assessment and check with your teacher before starting any practical work.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 18 January 2006
