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Hypergolic

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Hygroscopic

Definition

• A hygroscopic material (literally "water seeking") is one that readily absorbs water (usually from the atmosphere).

In most cases, the water can be removed from the material by heating (sometimes under vacuum or under a flow of dry gas such as nitrogen).

Additional Info

We carry laboratory drying tubes and related equipment at Safety Emporium.

Hygroscopic substances that are used to remove water from the surroundings are called desiccants. For example, those small packets marked DO NOT EAT that come with items such as electronic goods contain silica gel to absorb atmospheric moisture and prevent it from condensing on the product when the temperature falls. In the laboratory, anhydrous hygroscopic substances such as calcium chloride (CaCl2), magnesium sulfate (MgSO4), and sodium sulfate (Na2SO4) are used to remove residual water from organic solutions. In this application, the solid is added to the solution. After a few minutes, the solid desiccant (now partially hydrated) is removed by filtration or decanting. Hygroscropic drying agents are also used in desiccators, sealed jars that have a layer of desiccant in the bottom. They are also used in drying tubes which are stuffed with the desiccant material and placed over the opening of a chemical apparatus to keep atmospheric moisture out.

MSDS Relevance

Hygroscopic materials are fairly common. Some may absorb a finite amount of water (such as magnesium sulfate, MgSO4) while others may attract so much water that they form a puddle and dissolve (deliquesce). For example, solid sodium hydroxide (NaOH) pellets will form a small corrosive puddle in less than an hour in moist air. The CU Boulder link below has a great picture of this phenomenon. Therefore, always be sure to clean up any spills of hygroscopic materials right away. Also be aware that hygroscopic materials typically release a large amount of heat when mixed with water. Always store hygroscopic materials in well-sealed containers (or under vacuum or an inert atmosphere). Know their physical properties so that if you open a container you can tell if the material has been contaminated with water (i.e. that jar of calcium chloride, CaCl2, should be a solid, not a liquid).

Get your water-reactive signs and labels at Safety Emporium.

Further Reading

• Drying Organic Solutions at CU Boulder. Check out the great pictures.
• J.T. Baker (Mallinckrodt Baker) has a handy Desiccant Selection Guide.
• Common desiccant types at SorbentSystems.com. See the Quick Links box for additional information.
• Desiccants/sorbents, a list of reports pertinent to product packaging at Healthcare Paackaging.

See also: Anhydride, anhydrous, water reactive.

Additional definitions from Google and OneLook.

Disclaimer: The information contained herein is believed to be true and accurate, however ILPI makes no guarantees concerning the veracity of any statement. Use of any information on this page is at the reader's own risk. ILPI strongly encourages the reader to consult the appropriate local, state and federal agencies concerning the matters discussed herein.