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Anhydrous

A substance is anhydrous if it contains no water, for example, salts lacking their water of crystallization. The way of achieving the anhydrous form differs from one substance to another.

Solvents

In many cases, the presence of water can prevent a reaction from happening, or it can cause undesirable products to form. To prevent this, anhydrous solvents must be used when performing certain reactions. Examples of reactions requiring the use of anhydrous solvents are the Grignard reaction and the Wurtz reaction. Solvents are commonly rendered anhydrous by boiling them in the presence of a hygroscopic substance; metallic sodium is one of the most common metals used. Other methods include the addition of molecular sieves or alkali bases such as potassium hydroxide or barium oxide. Column solvent purification devices (generally referred to as Grubb's columns) recently became available, reducing the hazards (water reactive substances, heat) from the classical dehydrating methods. Guidelines for solvent purification at UC Davis

Gases

Several substances that exist as gases at standard conditions of temperature and pressure are commonly used as concentrated aqueous solutions. To clarify that it is the gaseous form that is being referred to, the term anhydrous is prefixed to the name of the substance:

See also

References

"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Anhydrous, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Anhydrous&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany