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Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Although ammonia contributes significantly to the nutritional needs of the planet, the gas itself is toxic.

Ammonia used commercially is usually named anhydrous ammonia. This term, although redundant, emphasizes the absence of water. Because NH3 boils at -33 C, the liquid must be stored under pressure and/or at low temperature. Its heat of vapourisation is, however, sufficiently high that NH3 can be readily handled in ordinary beakers in a fume hood. "Household ammonia" or "ammonium hydroxide" is a solution of NH3 in water. The strength of such solutions is measured in units of baume (density), with 26 degrees baume (about 30 weight percent ammonia at 15.5 °C) being the typical high concentration commercial product.[2] Household ammonia ranges in concentration from 5 to 10 weight percent ammonia. See Baumé scale.



[edit] Structure and basic chemical properties
The ammonia molecule has a trigonal pyramid shape, as predicted by VSEPR theory. This shape gives the molecule an overall dipole moment and makes it polar so that ammonia readily dissolves in water. The nitrogen atom in the molecule has a lone electron pair, and ammonia acts as a base, a proton acceptor. In water a very small percentage of NH3 is converted into the ammonium cation (NH4+). Thus, the term ammonium hydroxide is a misnomer. The degree to which ammonia forms the ammonium ion increases upon lowering the pH of the solution— at "physiological" pH (~7), about 99% of the ammonia molecules are protonated. Temperature and salinity also affect the proportion of NH4+. NH4+ has the shape of a regular tetrahedron.

The main uses of ammonia are in the production of fertilizers, explosives, and synthesis of organonitrogen compounds. It is also the active ingredient in household glass cleaners. Ammonia is found in small quantities in the atmosphere, being produced from the putrefaction of nitrogenous animal and vegetable matter. Ammonia and ammonium salts are also found in small quantities in rainwater, while ammonium chloride (sal-ammoniac), and ammonium sulfate are found in volcanic districts; crystals of ammonium bicarbonate have been found in Patagonian guano. The kidneys secrete NH4+ to neutralize excess acid. [3] Ammonium salts also are found distributed through all fertile soil and in seawater. Substances containing ammonia, or that are similar to it, are called ammoniacal.


[edit] History
Salts of ammonia have been known from very early times; thus the term Hammoniacus sal[4] appears in the writings of Pliny, although it is not known whether the term is identical with the more modern sal-ammoniac.[4]

In the form of sal-ammoniac, ammonia was known to the alchemists as early as the 13th century, being mentioned by Albertus Magnus.[5] It was also used by dyers in the Middle Ages in the form of fermented urine[5] to alter the colour of vegetable dyes. In the 15th century, Basilius Valentinus showed that ammonia could be obtained by the action of alkalis on sal-ammoniac. At a later period, when sal-ammoniac was obtained by distilling the hoofs and horns of oxen and neutralizing the resulting carbonate with hydrochloric acid, the name "spirit of hartshorn" was applied to ammonia.[5]

Gaseous ammonia was first isolated by Joseph Priestley in 1774 and was termed by him alkaline air; however it was acquired by the alchemist Basil Valentine.[6] Eleven years later in 1785, Claude Louis Berthollet ascertained its composition.


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For the Australian band of the same name, see Ammonia (band).
Ammonia

General
Systematic name Ammonia
Azane (See Text)
Other names Hydrogen nitride
Spirit of hartshorn
Nitrosil
Vaporole
Molecular formula NH3
Molar mass 17.0304 g/mol
Appearance Colourless gas with
strong pungent odour
CAS number [7664-41-7] [1]
Properties
Density and phase 0.6813 g/L, gas.
Solubility in water 89.9 g/100 ml at 0 °C.
Melting point -77.73 °C (195.42 K)
Autoignition temperature 651 °C
Boiling point -33.34 °C (239.81 K)
Acidity (pKa) 33.6
Basicity (pKb) 4.75
Structure
Molecular shape Terminus
Dipole moment 1.42 D
Bond angle 107.5°
Hazards
MSDS External MSDS
Main hazards Toxic and corrosive.
NFPA 704
130
Flash point None[1]
R/S statement R: R10, R23, R34, R50
S: S1/2, S16, S36/37/39,
S45, S61
RTECS number BO0875000
Supplementary data page
Structure and
properties n, εr, etc.
Thermodynamic
data Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Other ions Ammonium (NH4+)

hydroxide (NH4OH)

chloride (NH4Cl)
Related compounds Hydrazine
Hydrazoic acid
Hydroxylamine
Chloramine
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references
Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Although ammonia contributes significantly to the nutritional needs of the planet, the gas itself is toxic.

Ammonia used commercially is usually named anhydrous ammonia. This term, although redundant, emphasizes the absence of water. Because NH3 boils at -33 C, the liquid must be stored under pressure and/or at low temperature. Its heat of vapourisation is, however, sufficiently high that NH3 can be readily handled in ordinary beakers in a fume hood. "Household ammonia" or "ammonium hydroxide" is a solution of NH3 in water. The strength of such solutions is measured in units of baume (density), with 26 degrees baume (about 30 weight percent ammonia at 15.5 °C) being the typical high concentration commercial product.[2] Household ammonia ranges in concentration from 5 to 10 weight percent ammonia. See Baumé scale.