Distillation Methods

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Fractional Distillation setup

How to grease ground glassware joints

Simple Distillation Setup
This photo shows the complete setup for a simple distillation.

•Note that the bottom hose is connected to the water tap and the top hose leads the water into the sink. (The drain hose is held in place at the sink end to avoid floods; here a loose-fitting iron ring has been used.) (A few drops of acetone will help the hoses to slide onto the glass hose nipples.)

Make sure to keep the water flow at a minimum to avoid overflow of the sinks.

•Grease all ground glassware joints as you assemble the apparatus.

•A graduated cylinder is used as the receiver in Experiment E, but usually a tared vial or flask is used to collect distillate.

IMPORTANT NOTES ON CLAMPING: The utility clamp on the condenser is just there to keep it from swinging around; it must be loose-fitting and neither push up or down on the condenser!! Over-clamping of an apparatus, or the use of horizontal (and not only vertical) bars for clamp supports, are common beginner's errors which are to be avoided. In the photo, a ring stand was used to support the condenser clamp (not the horizontal bar.)

The only tightly fitted clamp is the one on the neck of the distillation flask.

 

•The position of the thermometer is crucial: The entire mercury bulb must be positioned below the bottom of the orifice leading to the condenser. This ensures that the entire mercury reservoir is immersed in the rising vapors and that the temperature is accurate. (SAFETY TIP: A light coating of grease will help the thermometer to slide easily into the neoprene adapter - don't use force!)

•The Thermowell (ceramic heating mantle) sits atop an iron ring, and should fit snugly against the flask. Keep it turned off until ready to distill.

•The clamp holding the distillation flask is tight, and the wing nut at the back of the clamp is set so as to prevent clamp rotation.

•Properly greased joints have just enough stopcock grease to give a uniformly clear appearance; more below...........

•When assembled, ground glass joints are transparent; there should be no streaking of the grease. This assures a leak-proof seal. A well-greased joint can hold a vacuum for years!

•A metal spring-clamp ("Kem clamp") is often useful for holding a glass joint together.

In this photo, two clamps are being used to hold glassware in place. This is really more than necessary; provided there are no upward forces on the condenser, gravity will hold the still head in place.

A plastic clamp (usually blue) is easier to use, but can only be employed where the temperature is less than 130C, such as at the bottom of the condenser, or it will melt! The previous photo shows a blue plastic clamp holding the vacuum adapter - of course, a metal one could be used instead.

©2001,2002 Daniel A. Straus

After setup is complete, remove thermometer and adapter carefully and, using a funnel, pour your unknown alcohol ("distilland") into the round-bottom flask. Be sure there are a few (3-5) boiling chips in there too!

You are now ready to start your distillation. Check the following:

•The apparatus is stable.

•The condenser water is flowing slowly.

•The Thermowell is plugged into the Powermite temperature regulator and is in close contact with the distillation flask.

•The thermometer is at the correct height.

SAFETY NOTE: When finished with the distillation, let the apparatus cool before disassembling. The Thermowell can be carefully removed while still hot and replaced with a water bath to cool the flask.

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