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How to Speed Up Evaporation

All liquids will undergo some degree of evaporation if they sit in an open container. Evaporation occurs when molecules at the surface of the liquid gain enough energy to detach themselves from the bulk fluid and leave as vapor. Several factors will increase the rate of evaporation, including raising the liquid temperature, lowering the ambient atmospheric pressure and increasing the surface area of the liquid. You can speed up the evaporation rate of a liquid, such as a lab solvent, by employing a combination of heat and vacuum.

Things You'll Need

Side-arm vacuum flask
Rubber stopper
Rubber hoses
Vacuum source
Cold trap with isopropanol/dry ice
Ring stand and clamp
Hot water bath
Boiling chips

Instructions

- 1
  Pour the liquid to be evaporated into the side-arm vacuum flask, taking care to only fill it 1/3 full or less. This prevents the liquid from accidentally being drawn into the vacuum line if it bubbles or foams during evaporation. Add a few boiling chips to prevent bumps or splashes in the event the liquid boils.
- 2
  Seal the opening of the flask with a rubber stopper and clamp the flask in place, attached to the ring stand, to prevent it from tipping over.
- 3
  Attach a thick-walled rubber hose to the vacuum inlet of the flask, then attach the other end of this hose to the inlet of a cold trap clamped to a ring stand. Attach a second hose between the outlet of the cold trap and a vacuum source, such as a pump. Immerse the cold trap in isopropanol/dry ice to cool it.
- 4
  Turn on the vacuum source so that vacuum is applied to the flask. Depending on the liquid, it may begin to bubble or foam. You may slightly loosen the clamp and gently swirl the flask to promote more even or more efficient evaporation.
- 5
  Observe the flask to see the rate at which the liquid is evaporating. If, after several minutes, there is no appreciable evaporation, loosen the clamp on the flask and slide the hot water bath underneath, then insert the flask in the water bath and re-tighten the clamp. The applied heat will speed up the evaporation further.
- 6
  Observe the flask, with some intermittent swirling, until all the liquid has evaporated. Turn off the vacuum source, then disconnect the rubber hoses. Empty the cold trap into a suitable hazardous waste container, taking care when handling the extremely cold trap components.

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