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The Purpose of a Calcium Chloride Drying Tube

John Brennan

Certain experiments in organic chemistry involve reactions that must be carried out in the absence of water. Unfortunately, air contains moisture. The solution to this problem is a drying tube.

Drying tubes are useful for certain experiments in organic chemistry.

Calcium Chloride

Anhydrous calcium chloride is a very hygroscopic compound, meaning that it readily absorbs water. It can even dissolve, in fact, in the water it absorbs from the surrounding atmosphere. Calcium chloride pellets in a drying tube act as desiccants or drying agents, removing moisture from the air that flows through them.

Features

A calcium chloride drying tube contains calcium chloride pellets at the top and bottom, held in place by plugs made of glass wool. As air flows through the wool and the calcium chloride, it is de-humidified so that the air entering the reaction chamber contains little or no moisture.

Significance

A reaction involving gases could potentially shatter a sealed vessel; it may not be desirable, however, to allow air moisture to enter the chamber. A drying tube relieves pressure inside the reaction vessel by allowing gases to escape while preventing moisture from contaminating the reactants.

The Drip Cap

  • Certain experiments in organic chemistry involve reactions that must be carried out in the absence of water.
  • Unfortunately, air contains moisture.
  • As air flows through the wool and the calcium chloride, it is de-humidified so that the air entering the reaction chamber contains little or no moisture.