Practical investigations
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To find the concentration of ethanol, using the back titration method, why does the wine need to be distilled?
Igloo replies
I’m not sure which “back titration” you are using, but it could well be the method in which you oxidise the wine distillate with an excess of acidified dichromate(VI), followed by a back titration with a standard solution of iron(II) ions. I shall assume that this is the case.
Potassium dichromate(VI) is a strong enough oxidising agent to oxidise several other components of the wine as well as the ethanol. The distillation process separates off the ethanol from most of these other components, and ensures that the dichromate ions only react with ethanol molecules. Of course, there may well be some oxidisable compounds which distil over with the ethanol, but fortunately most of them are relatively non-volatile and remain in the wine.
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Risk assessment
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updated: 24 January 2006
