100.0 kg of a mixture of ethanol and water, with 40 % ethanol by mass, is distilled in a very tall…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
of a mixture of ethanol and water, with ethanol by mass, is distilled in a very tall column. The top product is the azeotrope, with ethanol by mass. All the ethanol goes to the top, and the bottom product is pure water. Find the mass of azeotrope and the mass of water.
Need a reminder? The key ideaShow
An azeotrope boils at one temperature and has the same composition in the liquid and in the vapour, so distillation cannot separate it. Positive deviation gives a minimum-boiling azeotrope, which comes off at the top of a column. Negative deviation gives a maximum-boiling azeotrope, which stays at the bottom.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Balance the ethanol, then balance the total mass.
Step 1. The ethanol. The feed holds of ethanol.
Step 2. The azeotrope. It holds ethanol, so its mass is .
Step 3. The water. The rest of the feed is water: .
Answer: of azeotrope and of water.
Watch out. However tall the column, the top product is never purer than ethanol.
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