Information about Anhydrous
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.
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]
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. On heating, it undergoes the following reaction:
MgSO4·7H2O + heat → MgSO4 + 7H2O
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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.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 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. 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. To clarify that it is the gaseous form that is being referred to, the term anhydrous is prepended 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.
References
Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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The Grignard reaction, named for the French chemist François Auguste Victor Grignard, is an organometallic chemical reaction involving alkyl- or aryl-magnesium halides, also called Grignard reagents, with electrophiles.
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The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers, whereby two alkyl halides are reacted with sodium to form a new carbon-carbon bond:
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Sodium (IPA: /ˈsəʊdiəm/) is a chemical element which has the symbol Na (Latin: natrium), atomic number 11, atomic mass 22.9898 g/mol, common oxidation number +1.
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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 small enough to pass through the pores are adsorbed while larger molecules are not.
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Molecules small enough to pass through the pores are adsorbed while larger molecules are not.
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The chemical compound potassium hydroxide (KOH), sometimes known as caustic potash, potassa, potash lye, and potassium hydrate, is a metallic base.
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Barium oxide, BaO, is a white hygroscopic compound formed by the burning of barium in oxygen, although it is often formed through the decomposition of other barium salts.
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Copper(II) sulfate ("sulphate" in most Commonwealth nations) is the chemical compound with the formula CuSO4. This salt exists as a series of compounds that differ in their degree of hydration.
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Water of crystallization (alt. Br.E. water of crystallisation) is water that occurs in crystals but is not covalently bonded to a host molecule or ion. The term is archaic and predates modern structural inorganic chemistry, coming from an era when the relationships between
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In chemistry and other sciences, STP or standard temperature and pressure is a standard set of conditions for experimental measurements, to enable comparisons to be made between sets of data.
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Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of the planet as a precursor to foodstuffs and fertilizers.
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hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry.
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