As a general term, a substance is said to be anhydrous if it contains no water. Water is a common Chemical substance that is essential for the survival of all known forms of Life. The way of achieving the anhydrous form differs from one substance to another.
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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. The Grignard reaction, named for the French chemist François Auguste Victor Grignard, is an organometallic Chemical reaction in which Alkyl - The Wurtz reaction, named after Charles-Adolphe Wurtz, is a Coupling reaction in Organic chemistry, Organometallic chemistry and recently inorganic
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. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Other methods include the addition of molecular sieves or alkali bases such as potassium hydroxide or barium oxide. A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for Gases and Liquids Molecules Potassium hydroxide is the Inorganic compound with the formula K[[hydroxide OH]] Barium oxide, BaO is a white Hygroscopic compound formed by the burning of Barium in Oxygen, although it is often formed through the decomposition 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. Copper(II sulfate is the Chemical compound with the formula Cu[[Sulfur S]] O 4 If the water of crystallization is removed from blue crystals of copper (II) sulfate, a white powder (anhydrous copper(II) sulfate) is formed. Water of crystallization (alt BrE water of crystallisation is Water that occurs in Crystals but is not covalently bonded to a host Molecule
The formula for anhydration of pentahydrate copper (II) sulfate (CuSO4·5H2O) is as follows:
CuSO4·5H2O + heat → CuSO4 + 5H2O
Another example is in the heating of magnesium sulfate heptahydrate, MgSO4·7H2O. Magnesium sulfate is a Chemical compound containing Magnesium and Sulfate, with the formula MgSO4 On heating, it undergoes the following reaction:
MgSO4·7H2O + heat → MgSO4 + 7H2O
Gases
Several substances that exist as gases at standard conditions of temperature and pressure are commonly used as concentrated aqueous solutions. In Physical sciences standard conditions for temperature and pressure are Standard sets of conditions for experimental measurements to allow comparisons to be made 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. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor See also Ammonia Ammonium hydroxide (NH3 also known as ammonia water, aqua ammonia, or aqueous ammonia, is a solution of
- 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
Air-free techniques refer to a range of manipulations in the chemistry Laboratory for the handling of compounds that are Air-sensitive.Dictionary
anhydrous
-adjective
- having little or no water
- (chemistry) having no water of crystallization
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