Ammonium hydroxide

Ammonium hydroxide, also known as ammonia or ammonia water, are aqueous solutions of ammonia (NH3) different concentrations. The solutions are colorless, have a pungent odor and a basic reaction. A concentrated solution is corrosive. The solutions have the CAS number 1336-21-6.

The common term is misleading ammonium hydroxide, a chemical compound NH4OH does not exist.

Other Names

Ammonia solution, ammonia water (often 10 % solution ), ammonia liquor, caustic ammonia (obsolete, obtained by caustification ), ammonia ( popularly derived from ammonium chloride) or hartshorn ( popularly derived from ammonium carbonate ), caustic ammonia, ammonium hydrate, Liquor ammonii caustici ( latin, used in medicine )

History

Ammonia has been known to the ancient Egyptians and Arabs. More on the history, see ammonia.

After the outdated idea of ​​Arrhenius model was a base ( alkali ) to mean a compound that can release hydroxide ions in water. In order to explain the behavior of ammonia was assumed that ammonia would form ammonium hydroxide in water molecules:

These molecules dissociate in to an equilibrium reaction, partially in ammonium ions and hydroxide ions:

This idea was the - compared to bases such as sodium - only weak basic (alkaline ) effect are explained. Although this idea did not correspond to reality, they provided the basis for the emergence of the term " ammonium " for aqueous solution of ammonia.

Properties

Ammonia dissolves very well in water, much better than other gases such as oxygen or carbon dioxide. The solubility is dependent on the temperature and the partial pressure of the gaseous ammonia. One liter of water takes at 0 ° C and a pressure of 1 bar 880 g ( 1142 l ) at 20 ° C, 520 g, at 40 ° C is about 340 g and at 100 ° C only 75 g of gaseous ammonia. The enthalpy of solution of ammonia at 25 ° C is -30.64 kJ / mol.

Of ammonia, ammonia water evaporates due to its higher vapor pressure much faster than water, and therefore the concentration of ammonia decreases in open vessels with time. Here, the typical, piercing sharp ammonia odor occurs. The vapor pressure of a 25 % solution at 20 ° C at 483 hPa by heating a solution of ammonia can be easily cast. The boiling point of a 25 % solution is only at 37.7 ° C, that of a 32 % solution at 24.7 ° C

The density and the freezing point of ammonia water falls with increasing content of ammonia, see table.

Under dilute ammonia is in the laboratory often a 1 - to 2 - molar solution (mass fraction 1.75 to 3.5 %) and concentrated ammonia solutions with commercially available concentrations of 16.5 mol / L (32 %) or 13.4 understood mol / L ( 25%).

At low temperature, ammonia hydrate ( NH 3 · H 2 O ) can be isolated which melts at -79 ° C. It is crystalline ammonia with unattached water.

Dilution and acid -base reaction

In aqueous solutions, the bulk of the ammonia is dissolved molecularly. Between water and ammonia molecules contribute hydrogen bonds. They are the cause of the high solubility and act on the hydrogen and the nitrogen atoms of ammonia:

In an acid -base reaction between ammonia and water, ammonium (NH4 ) and hydroxide form (OH - ):

The balance is clearly in the left side of the reaction. The base constant KB

Of ammonia is 1.75 x 10-5 ( pK = 4.75). This ammonia is only a medium strong base. The degree of dissociation of a 0.1 molar solution is less than 1% of a 1 molar solution is 0.4%.

Use

Ammonia is used for cleaning surfaces in the household and in the art. In engineering, for example, for cleaning of galvanized steel for subsequent painting ( ammonia wetting agent ).

In the bleaching and dyeing in the ammonia is used as a cheap basic solution.

Ammonium hydroxide is used as an acidity regulator in food chemistry and also serves the digestion of milk protein, cocoa products and egg products. The food additive marking E 527

From leftover meat obtained Pink Slime, is freed by the addition of ammonium hydroxide of salmonella and E. coli bacteria, and thus only for human consumption. At least one fast-food chain used e 527 in higher quality meat products in order to maintain a high quality standard.

The Kalina cycle is dependent on the mixing ratio of the ammonium hydroxide lower boiling point to drive steam turbines is used with low temperatures and the associated increase in effect.

Safety

S: (1/ 2) - 26 - 36/37/39 - 45 - 61

The labeling data in the table refer to the concentrated and dilute aqueous solutions. For identification of pure ammonia, see there. From 5 % solutions of ammonia water is classified as irritant, from 10 % solutions as corrosive.

Ingestion of ammonia water causes severe pain, gastritis, vomiting blood, lung and vocal damage, which often have fatal outcome. It attacks the eyes.