Condenser

A condenser is a piece of laboratory glassware used for converting vapors to liquids. A condenser generally consists of a path for the vapors and a separate path for the coolant which flow adjacent to each other, although there are many different designs for different purposes. Most of the time, cold water will be run through the coolant path of the condenser. This can be done using a bucket of ice water and an aquarium or fountain pump, attached to the condenser with rubber tubing. The coolant always flows in through the bottom of the condenser and out through the top. This prevents irregular flow and air bubbles, and keeps the condenser completely filled with coolant at all times.

Uses for Condensers

Condensers are mainly used for two purposes- reflux and distillation.

Reflux

Reflux is the process of continuously boiling and condensing a liquid or solution without letting any vapor escape. It is often used for reactions that must take place at temperatures at or close to the boiling point of the solvent. While a simple reflux system can be made using a flask of cold water on top of a beaker, a more efficient method is to use a flask with a condenser attached directly to the top.

Recommended style: Friedrich's, Dimroth, or Alihn

Distillation

The most common use for condensers is for distillation. Distillation is the process of separating an impure mixture by carefully boiling and condensing the lower boiling fractions of it. For some substances, a short path distillation using an air (or sometimes cold pack) cooled distillation arm will work, but most of the time a more elaborate condenser is required.

Recommended style: Liebig, Alihn, or Graham

Types of Condensers

There are many types of condensers which all serve somewhat different purposes.

Liebig

The Liebig (or West) condenser is the simplest type of water cooled condenser. It consists of a straight tube as the vapor path which is surrounded by an outer jacket for the coolant path. While it is not the most efficient model, it is definitely the most versatile. It can be used for distillation or reflux, and can operate at nearly any angle. Because of its simplicity, it is also the most affordable. Every home chemist needs to have a Liebig condenser before considering any other type, as its versatility is unmatched.

Works for: Distillation, reflux

Alihn

The Alihn condenser is a modified version of the Liebig which works in almost the same way, except the vapor path consists of a series of bulbs instead of a simple tube, which substantially increase the surface area of the internal cooling surface. The downside to this design is that it can only be used vertically, otherwise condensed liquid will get stuck in the bulbs. Alihn condensers are mainly used for reflux applications. They are often used with Soxhlet extractors. They can be used for distillation, but must be kept vertical, which can be inconvenient in that scenario.

Works for: Reflux, distillation

Graham

The Graham condenser is a very highly efficient distillation condenser. The vapor path is a tightly coiled tube surrounded by a water jacket, so it acts like a very long Liebig condenser. The downside to the Graham condenser is that it can only be used for distillation. Because of the tightly coiled vapor path, if it is used as a reflux condenser, condensed liquid in the narrow path may block rising vapors causing pressure to build up which can be a serious problem. Like Alihn condensers, Graham condensers must always be used vertically so that distillate does not get trapped in the bends of the coils.

Works for: Distillation

Dimroth

The Dimroth (or coil) condenser consists of a coiled internal tube that the coolant flows through which the vapors pass over. It can be seen as an inverted Graham condenser. Dimroth condensers work very well for reflux since they have a high cooling surface area and allow condensate and vapor to easily move past each other. Oftentimes the coil has a kink at the bottom to allow the condensate to uniformly drip back into the reaction vessel when refluxing.

Works for: Reflux

Friedrich's

The Friedrich's condenser is a complex type of condenser that is very efficient and can be used for both reflux and distillation. It consists of an internal cold finger that is filled with coolant that has a spiral path shaped into it which the vapor phase flows onto. Condensate flows down the spiral path, but pressure does not build up during refluxing like in a Graham condenser because the path is somewhat wider, and in many Friedrich's condensers there is a small space between the cold finger and the outer wall of the condenser that allows vapor to flow around the condensate. The problems with the Friedrich's condenser are that it is quite expensive due to its complexity, and its strange shape makes it somewhat awkward to fit into a distillation setup.

Works for: Reflux, distillation

Cold Finger

A cold finger is a special type of condenser meant for converting vapors directly to solids for purifying substances that sublime. It is simply a tube with coolant circulating through it that is placed over a vessel in which a substance is being sublimed. The purified substance is deposited on the surface of the cold finger where it sticks. In many cases, a flask of cold water placed on a beaker would work as an easy improvised solution, but the cold finger condenser is more efficient since the water circulates.

Works for: Sublimation

Dewar

A Dewar condenser is a special condenser that doesn't have a continuously flowing coolant and instead has an open reservoir that can be filled with a very cold substance such as dry ice or liquid nitrogen. It is used for chilling substances to lower temperatures than normal condensers can manage, and is often used for condensing substances that are normally gases at room temperature.

Works for: Special