Ammonium
The ammonium ion NH4 ( IUPAC also Azanium ion ) is a cation which forms such as chemically similarly reacting the alkali metal ions, and salts of corresponding formula, for example, ammonium nitrate ( ammonium nitrate ), ammonium chloride or NH4NO3 ( ammonium chloride). It is the conjugate acid of the base ammonia NH3.
Properties
The ammonium ion is constructed tetrahedrally. Ammonium forms a dissociation equilibrium with ammonia. Because of the involvement of an oxonium ion, this balance is the pH -dependent. The proportion of ammonia increases with increasing pH and increasing temperature.
The pKa of ammonium is 9.2. Ammonium salts (eg, ammonium sulfate) react in aqueous solution as weak acids and therefore are liable to form acidic solutions.
The nitrogen atom of the ammonium can be relatively easily oxidized to nitrogen. A typical example is the thermal decomposition of ammonium dichromate.
Ammonium salts described in the literature often described as a pseudo- alkali metal salts, resulting from their similar properties to the alkali metal salts. This analogy can be explained primarily by a nearly identical ionic radius and the same charge. They are similar, especially in their solubility in water, the alkali metal salts.
Ammonium in nature
In nature, ammonia results primarily in the degradation of proteins. So it is of fish and most other aquatic organisms, resigned as the final product, eg via the gills. Also, in the bacterial decomposition of dead biomass, it is released as a final product. It plays an important role in the citric acid cycle, in which it reacts with α -ketoglutarate to glutamic acid.
Ammonium is in the ground and in waters under oxygen consumption by bacteria (eg Nitrosomonas ) first to nitrite and from another bacterial species (eg Nitrobacter ) further oxidized to nitrate and thus " detoxified ". In addition to bacteria and archaea play an important role in the oxidation of ammonium in the soil. This process is called nitrification and is in the floor quite desirable. Also in the aquatic nitrification is an important part of self-purification.
Ammonia is toxic to fish even at low concentrations. Ammonium concentrations in the water of 0.5 to 1 mg / l are therefore depending on the pH of the water, classified as a concern for fish. When ammonium levels above 1 mg / l of a water body for fishing purposes is not appropriate.
Physiological significance
The ammonium ion is similar to the potassium ion ( K ) in both size and charge and can therefore take its place in the organism. However, since it reacts differently, eg of synapses, which are potassium- controlled, can not be removed again, it blocked it permanently. It therefore acts in all organisms with potassium- controlled synapses as a neurotoxin.
Ammonium in the urine indicates concretions.
Use
Ammonium salts are the main compounds of the inorganic chemical industry. They are produced in megaton scale and mainly used as fertilizer, and to a lesser extent also in dry batteries and dyes.
The ammonium salt of thioglycolic acid is used as a reducing agent in the permanent waving. The ammonium salt of thiolactic is another example from organic chemistry and is also used in hairdressing.
Proof
To test ( laboratory test ) of a substance is added to ammonium hydroxide or sodium hydroxide them with something. The liberated ammonia smell either you or it can show by means of the basic coloration of a moist pH test strip to the reaction mixture ( crossmatch ).
A sensitive test is the reaction with Nessler's reagent, which responds but also to amines. A sensitive and selective quantitative determination is carried out according to DIN mostly using the Berthelot reaction to form a blue indophenol, its concentration can be measured colorimetrically.
Organic chemistry
Tetra- methyl ammonium chloride and triethylamine hydrochloride are examples of organic ammonium salts, in which the nitrogen atom also has four binding partner, but they are organic radicals, or partly and hydrogen atoms, such as in hydrochlorides, hydrobromides or Hydroiodiden.