Practical investigations
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I am currently doing my vinegars coursework, and am studying the concentration of ethanoic acid in different vinegars. I am using distillation, and was wondering why the water and ethanoic acid 'condense off' together rather than at separate temperatures.
Igloo writes
Both ethanoic acid and water are volatile, so it’s hardly surprising that molecules of both distil off together. If you dissolve some salt or sugar, or some other non-volatile substance in a sample of water, then, of course, only the water can distil off, but when two or more volatile components are mixed together the distillate will always consist of a mixture of all of these.
Simple distillation of a mixture of liquids always produces a mixture in the distillate. Fractional distillation allows a better separation but the close affinity between water and ethanoic acid, thanks to hydrogen bonding, makes them hard to separate. You would need to explore the theory of the vapour pressure of non-ideal mixtures to understand this fully.
You will find some interesting information on the distillation of liquid mixtures in the Nuffield Chemistry Chemical Engineering Special Study booklet. We are going to be putting this on Re:act, but it's not there yet.
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: 13 January 2004
