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I am trying to find a good mixture (materials and proportions)for teaching
my students how to fractionally distill two liquids. I want them to have
this knowledge and skill before they begin an Identification of Unknown
Substances unit. I have used ethyl alcohol and water in varying
proportions with little success, and the department chair is starting to
get grumpy with the volume of resources I am using.
First, your problem is that ethyl alcohol and water form an azeotrope. If you have too much alcohol, you will only see one boiling point; if you have too much water, you will distill off all your ethyl alcohol as the 190-proof azeotrope and leave pure water behind. But there's many a slip 'twixt the cup and the lip... and I'd bet that you are having problems getting the residual water to distill properly. You'd be better off using a mixture of methanol (methyl or "wood" alcohol) and water; this doesn't form a low-boiling azeotrope. Or you might consult the CRC Handbook's table of azeotropes for more ideas.
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