Ammonia is the hydride of nitrogen, i.e. nitrogen hydride. It has the formula NH3. Its structure is not trigonal planar, but tetrahedral.
Strictly speaking, it is a tetrahedral cutout. Compared to the ideal tetrahedron (like in methane), a free electron pair forms the fourth tetrahedron tip.
At room temperature, ammonia is a colorless, highly corrosive gas. Fortunately, since it smells very pungent, accidents are rare. The carrion beetle Phosphuga seems to know this: it has a 4.5% aqueous solution of ammonia ready as a chemical weapon for its enemies.
Ammonia has been known since ancient times. The name goes back to the Egyptian god Ammon. The name ammonium chloride also comes from this time: Sal ammoniacum.
Basic compounds of ammonia
Ammonia combines with acids to form ammonium salts (-> experiment). The ammonium ion is tetrahedral.
This is also an example of a classic acid / base reaction. Ammonia often reacts as a base.
But it can also act as an acid: If you replace the hydrogen atoms in ammonia with metal atoms, you get metal amides (MNH2), imides (M2NH) and nitrides (M3N), where M stands for a monovalent metal.
So ammonia is an ampholyte. Therefore, as in water, autoprotolysis also takes place with pure, liquid ammonia:
2 NH3 <-> NH4+ + NH2–
The replacement of the hydrogen atoms by one, two, three or four organic radicals (-R) leads formally to primary, secondary, tertiary or quaternary amines.
Aqueous solutions of ammonia
Ammonia dissolves very well in water. This can be clearly illustrated in the ammonia fountain experiment. 1 liter of water at 20°C can absorb up to 520 g of ammonia. That’s about 500 liters of gas.
This aqueous solution of ammonia is called ammonia water. This contains ammonium hydroxide (NH4OH), which is not stable on its own.
NH3 + H2O —> NH4+ + OH–
Diluted ammonia solutions have an ammonia content of around 10%. This solution is used as a cleaning agent due to its alkaline properties. Ammonia also serves as an alternative remedy for insect bites.
This effect of ammonia is due to the fact that its aqueous solution contains hydroxide ions (OH–). This is also the result of an acid / base reaction.
In contrast to other alkalis such as sodium hydroxide (NaOH), ammonia is also often referred to as a volatile base, since the gaseous ammonia escapes completely when it is heated.
How do you make ammonia?
In nature, ammonia is created through the anaerobic breakdown of nitrogen-containing organic substances. In addition, during nitrogen fixation and the assimilation of nitrates by microorganisms, elemental nitrogen and inorganic nitrates are converted into ammonia.
However, ammonia is rarely found in nature in its free form. It is usually quickly converted into organic compounds (such as urea or uric acid) or enzymatically oxidized to nitrates (nitrification).
Ammonia has also been found in space, for example in the Milky Way and in the atmosphere of the large gas planets.
In the laboratory, ammonia is produced by heating ammonia water or a mixture of ammonium chloride and calcium hydroxide.
2 NH4Cl + Ca(OH)2 —> CaCl2 + 2 NH3 + 2 H2O
For a long time, ammonia was only available from the coking plant wastewater when extracting natural gas. Today you can produce huge amount using the Haber-Bosch process. In the Haber-Bosch process, elemental nitrogen and hydrogen are converted at high pressure and high temperature with the help of catalysts.
All ammonia production plants in the world work according to this basic principle.
What do you need ammonia for?
Ammonia is a very common chemical in industrial chemical synthesis. For example, it is used to manufacture urea, sulfonamides, polymer fibers, sodium cyanide, hydrogen cyanide and nitriles, soda using the Solvay process, aminoplasts, nitric acid and nitrates, as well as ammonium salts for fertilizers (especially as ammonium sulfate).
Liquid ammonia boils at -33.4 ° C. Because of its high evaporation heat (1.26 kJ/g), ammonia is therefore suitable as a coolant in refrigerating machines (refrigerators).
How do I recognize ammonia?
Its unpleasant pungent odor is characteristic. Even in low concentrations, the gas is particularly irritating to the eyes.
Ammonia reacts with many common indicators, due to the formation of hydroxide ions. You can recognize it by the blueing of moist, red litmus paper that you hold in the vapor space above the solution (-> experiment).
The formation of colorless smoke (which consists of solid NH4Cl) is known when approaching a vessel that contains concentrated hydrochloric acid (-> experiment).
In aqueous solution, when copper sulphate solution is added, NH3 gives the characteristic deep blue coloration of tetraammine copper(II)sulfate ([Cu(NH3)4]SO4) (-> experiment).