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anhydrous

 
Dictionary: an·hy·drous   (ăn-hī'drəs) pronunciation
adj.
Without water, especially water of crystallization.

[From Greek anudros : an-, without; see a-1 + hudōr, water.]


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Chemistry Dictionary: anhydrous
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Denoting a chemical compound lacking water: applied particularly to salts lacking their water of crystallization.



Thesaurus: anhydrous
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adjective

    Having little or no liquid or moisture: arid, bone-dry, dry, moistureless, sere, waterless. See dry/wet.

Dental Dictionary: anhydrous
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(anhī′drus)
adj

Without water.

Veterinary Dictionary: anhydrous
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Containing no water.

  • a. lanolin — the principal animal fat used in the preparation of ointments for animals. Now competes with synthetic materials such as polyethylene glycols.
Wikipedia: Anhydrous
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As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another.

Contents

Solvents

In many cases, the presence of water can prevent a reaction from happening, or form undesirable products. 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.[1]

Ionic crystals

An example of anhydration can be seen in copper(II) sulfate. If the water of crystallization is removed from blue crystals of copper (II) sulfate, a white powder (anhydrous copper(II) sulfate) is formed.

The equation for dehydration of copper(II) sulfate pentahydrate (CuSO4·5H2O) is as follows:

CuSO4·5H2O → CuSO4.H2O + 4H2O

Another example is in the heating of magnesium sulfate heptahydrate, MgSO4·7H2O. On heating, it undergoes the following reaction:

MgSO4·7H2O → MgSO4 + 7H2O

These equations are said to be anhydrous equations

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:

  • gaseous ammonia is generally referred to as anhydrous ammonia to distinguish it from household ammonia, which is an ammonium hydroxide aqueous solution.
  • gaseous hydrogen chloride is generally referred to as anhydrous to distinguish it from the more commonly used 37% w/w solution in water.

See also

References

  1. ^ Guidelines for solvent purification at UC Davis

 
 

 

Copyrights:

Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
Chemistry Dictionary. A Dictionary of Chemistry. Sixth Edition. Copyright © Market House Books Ltd, 2008. All rights reserved.  Read more
Thesaurus. Roget's II: The New Thesaurus, Third Edition by the Editors of the American Heritage® Dictionary Copyright © 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.  Read more
Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.  Read more
Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Anhydrous" Read more