The Rotary Evaporator
Mark Niemczyk, PhD
The Lab Manual - Rotary Evaporator
Rotary Evaporator Procedure

It is commonly taught in General Chemistry classes that the vapor pressure of a liquid or solid varies directly with temperature, i.e., the higher the temperature of a substance, the higher its vapor pressure. When a liquid is heated it begins to boil as the liquid turns to vapor forming bubbles that literally "push away" the ambient atmosphere above the liquid surface. "Boiling" has occurred. The vapor pressure of the liquid became equal to the ambient pressure, counteracting it or pushing it away. We say the liquid is boiling.

Precise measurements of the temperature when a liquid boils may include other ambient pressures. The normal boiling point is that temperature where the vapor pressure of the liquid equals a standard atmosphere or 760 torr. Of course, as the pressure above a liquid at room temperature is steadily decreased, by, say, an aspirator pump, the liquid boiling point will also decrease, so much so that it will "boil" at room temperature, since that is where its vapor pressure equals the ambient pressure. You can consult books like the CRC Handbook of Chemistry and Physics for lists of organic compounds with vapor pressures at various temperatures to predict where a compound will boil at each applied ambient pressure.

The diagram below is a generic rotary evaporator. The essential parts are shown.

The rotary evaporator is used for removing a solvent well below its boiling point, leaving behind the less-volatile material that was dissolved in that solvent. This is especially essential for a less-volatile solvent which, if removed at atmospheric pressure would have to be heated so high that the solute dissolved in it would decompose on prolonged heating.If you carefully consider what each part of the rotary evaporator does, you ensure a safe, efficient removal of solvent.

Please learn how to use the rotary evaporator since you will be using it all year. It is not a good reflection on your lab proficiency if you have to ask how to use the rotary evaporator during the second semester. 

See the full lab manual here