distillations

The purpose of a distillation is to separate (and thus purify) one liquid from a mixture. This can be done by utilizing differences in boiling points of the components of the mixture. Think of separating water from a salt water mixture: water boils at 100 C, while salt boils at 600 C, so the water will boil off first. The water can be collected and condensed into pure water. A water distiller operates on this principle.

There are two main types of distillation apparatus that can be used in a basic organic chemistry lab - the simple still and the fractional still.

Here is a diagram of a simple still:



And here is a diagram of a fractional still:



A fractional still provides a much higher degree of purification due to the height of the vertical column above the mixture. This allows the vapor of the liquid having the lower boiling point to separate itself from the vapor of the liquid having the higher boiling point. In other words, the higher-boiling point liquid will remain in the vertical column and condense back into a liquid before reaching the horizontal condenser.



Here is a nice video that explains the advantages of the fractional still over the simple still:

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