Desiccator in Chemistry Lab: Definition, 

John Williams

Dessicators are used to dry chemicals before they are used in chemical reactions. This makes them important for scientists who use chemical reactions in laboratories. This article addresses dessicators, their properties, and how they work.

Introduction

Reactants are chemicals that can be combined to produce a chemical reaction, or change. Reactions, then, must depend on the nature and characteristics of the reactants involved. These characteristics include any changes that occur due to the environment around the reactants. One of these factors, water vapor, can cause major changes in reactants that absorb water, and therefore, must be controlled in order to allow the chemical reactions to occur properly. One way to do this is by using a dessicator.

What Is a Dessicator?

 A desiccator or desiccant container is a chamber that removes water from chemicals or items. It is extremely easy to make a desiccator yourself using materials you probably have on hand.

Have you ever wondered why so many products come with little packets that say 'Do Not Eat'? The packets contains silica gel beads, which absorb water vapor and keep the product dry, which is an easy way of preventing mold and mildew from taking their toll. Other items would absorb water unevenly (e.g., parts of a wooden musical instrument), causing them to warp. You can use the silica packets or another dessicant to keep special items dry or to keep water from hydrating chemicals. All you need is a hygroscopic (water-absorbing) chemical and a way to seal your container.

Common Desiccant Chemicals

• silica gel (the beads in those little packets)
• sodium hydroxide (sometimes sold as a solid drain cleaner)
• calcium chloride (sold as a solid laundry bleach or a road salt)

Make a Desiccator This is extremely simple. Just place a small amount of one of the desiccant chemicals into a shallow dish. Enclose an open container of the item or chemical you wish to dehydrate with the container of desiccant. A large plastic bag works well for this purpose, but you could use a jar or any airtight container.
The desiccant will need to be replaced after it has absorbed all of the water that it can hold. Some chemicals will liquefy when this occurs so that you will know they need to be replaced (e.g., sodium hydroxide). Otherwise, you'll just need to switch out the desiccant when it starts to lose its effectiveness.

A dessicator is a chamber or box that is designed to absorb water vapor from reactants that are hygroscopic. Hygroscopic reagents are able to absorb water. This can cause a problem when it comes to measuring the appropriate amounts of a particular chemical. The dessicator reduces this effect and helps to ensure accurate measurements of chemicals prior to the start of a chemical reaction. In other words, dessicators are used to dry any chemicals that may be used in reactions.

A Dessicator Containing a Dessicant 

Dessicators are usually sealed so that outside air cannot enter the chamber. In some cases, dessicators may also be fitted with a vacuum hose in order to remove excess air from the inside of the chamber. A dessicant, or drying material, is usually added to the dessicator to absorb water vapor whenever the dessicator is opened. Calcium chloride (a salt) and silica gel (a non-reactive solid) are two typical dessicants that are used routinely. The dessicants ensure that water vapor is absorbed before it reaches the reactants

Using a Desiccator

Purpose:

The desiccator is used to store dried samples in a dry atmosphere. It should not be used to dry an object, but to maintain an already dried object indefinitely in a dry condition.

Usage:

1. To open - slide lid horizontally across the top to one side until it comes off. Use one hand to hold the bottom of the desiccator while using the other hand to grasp the knob.
2. To close - place lid partly on the top and slide across until desiccator is completely closed and then rotate lid gently in both directions.
3. Do not attempt to lift lid off vertically.
4. Make sure the lid has enough grease around the ground glass rim - if necessary, spread Vaseline uniformly on the rim. When the lid is properly seated, the greased rim will appear as shown in Figure 2.
5. If the desiccant appears wet or clumpy, it probably needs to be replaced with new dessicant.  It is helpful to have a small amount of indicating desiccant present.  When the color changes to pink, the desiccant should be replaced.
6. Desiccants should be handled in the hood and added carefully, wearing goggles and lab coat. Desiccant should not coat the sides or plate of the desiccator.

Figure 1. Improperly sealed desiccator.
Note the cloudiness along the rim.

Figure 1. Properly sealed desiccator.
Note that the rim is clear.