can anyone explain how condensation and evaporation works in distillation?

Answer 1

In distillation you're exploiting the difference in boiling point for the two (or more) components. In the simplest explanation, let's assume you have two components (binary distillation). We'll call them A and B. If A boils at 100 degrees and B at 150 degrees, then we can use this to separate them. The most basic distillation apparatus is a round-bottom flask with a heat shroud around it and a vertical shaft with some coils around the top through which you flow some sort of cooler liquid, typically water. If you can maintain the temperature of the round bottom flask less than 150 degrees and keep the condenser at most 100 degrees, then "A" will want to boil off at the bottom, whereas "B" will not be so willing to boil. Unfortinately, some of "B" does end up in the gas and some of "A" doesn't boil out of the liquid.

It isn't hard to imagine how you could improve this by doing the distillation again on the liquid and gas parts, over and over to obtain a more pure sample. This is called multistage distillation and is the principle used in industrial distillation columns. In these, there are multiple trays (or packing material) which allow the gas and liquid to contact each other along the length of the column. During this process, some of the "heavy" components go back with the refluxing liquid. And some of the "light" components in the liquid go up with the gas. As you go up the column, you get more pure in the light key component and as you go down the column you get more pure in the heavy key.

Unfortunately, you can never get a 100% pure product from distillation. The closer you get to any pure component, the more stages you need. It's like the issue of taking half-steps towards the wall... you can never quite reach it. Distillation is also complicated by azeotropes (a point where the liquid and gas compositions are the same, thus no further separation occurs) as well as near-boiling components (that is, components with similar boiling points.. say 100 and 105 degrees).

Answer 2

In distillation you are boiling a mixture of compounds, each having a different boiling point. As the liquiid is heated up, eventually the substance with the lowest boiling point will start to boil - evaporate- out of the mixture. The vapors are collected and cooled, so the substance - condenses - back to a liquid again.

Answer 3

Wikipedia can explain all these sorts of questions