Ammonia water

safety instructions
Surname	Ammonia water
CAS number	1336-21-6
EC number	215-647-6
ECHA InfoCard	100.014.225
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 290-314-335-400 P: 260-273-280-301 + 330 + 331-303 + 361 + 353-305 + 351 + 338
MAK	20 ml m −3 , 14 mg m −3
Toxicological data	350 mg kg −1 ( LD 50 ,  rat ,  oral )

Ammonia water , also known as ammonia spirit , is the name for aqueous solutions of ammonia (NH ₃ ) of different concentrations . The solutions are colorless, have a pungent odor and are basic . Concentrated solutions are corrosive . Ammonia solutions have the CAS number 1336-21-6. The common name “ammonium hydroxide” is misleading because a chemical compound NH ₄ OH cannot be isolated.

other names

Ammonia solution, ammonia water (often 10% solution), ammonium hydroxide, ammonia lye, caustic ammonia (obsolete, obtained by causticizing ), salmiac spirit (popular, obtained from ammonia ), stag's horn (popular, obtained from stag's horn salt ), caustic ammonia, ammonium hydrate, liquor (Latin, used in medicine).

history

Ammonia was already known to the ancient Egyptians and Arabs. For more on the story, see under ammonia .

According to the outdated model by Arrhenius , a base ( alkali ) was understood to be a compound that can release hydroxide ions in water. To explain the behavior of ammonia, it was assumed that ammonia would form ammonium hydroxide molecules in water:

${\displaystyle \mathrm {NH_{3}+H_{2}O\ \longrightarrow NH_{4}OH} }$

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

${\displaystyle \mathrm {NH_{4}OH\rightleftharpoons NH_{4}^{+}+OH^{-}} }$

This idea could explain the basic (alkaline) effect - only weak compared to bases such as sodium hydroxide . Although this idea did not correspond to reality, it provided the basis for the emergence of the name "ammonium hydroxide" for aqueous solution of ammonia.

properties

Ammonia dissolves very well in water, significantly better than other gases such as oxygen or carbon dioxide . The solubility depends on the temperature and the partial pressure of the gaseous ammonia. One liter of water at 0 ° C and a pressure of 1 bar absorbs 880 g (1142 l), at 20 ° C 520 g, at 40 ° C 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.

Because of its higher vapor pressure, ammonia evaporates from ammonia water much faster than water, which is why the ammonia concentration in open vessels decreases over time. The typical, pungent-sharp ammonia odor occurs. The vapor pressure of a 25% solution at 20 ° C is 483 h Pa . Ammonia can be easily driven off by heating a solution. The boiling point of a 25% solution is only 37.7 ° C, that of a 32% solution is 24.7 ° C.

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

Content , molarity , density and depression of freezing point of ammonia water
Mass fraction in%	1	5	10	15th	20th	26th	30th
c (mol / L)	0.58	2.87	5.62	8.28	10.84	13.80	15.71
d (g / cm³)	0.996	0.979	0.958	0.941	0.925	0.906	0.894
∆ t (° C)	1.13	6.08	13.55	23.32	36.42	60.77	84.06

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

Concentrations of commercially available ammonia water almost always relate to the content of ammonia gas (NH ₃ ) in water and not to the content of "ammonium hydroxide" in water. A 25% solution of ammonia water accordingly contains 25 g of ammonia in 100 g of solution. Calculated in terms of “ammonium hydroxide”, which also absorbs a water molecule, this solution would be 51.5%.

Ammonia hydrate (NH ₃ · H ₂ O), which melts at −79 ° C, can be isolated at low temperatures . This is crystalline ammonia with attached water.

Solution process and acid-base reaction

In aqueous solutions, most of the ammonia is in molecular form . Hydrogen bonds act between water and ammonia molecules . They are the cause of the high solubility and act on the hydrogen and nitrogen atoms of ammonia:

${\displaystyle \mathrm {H_{2}O\cdots H-NH_{2}} }$

${\displaystyle \mathrm {HO-H\cdots NH_{3}} }$

In an acid-base reaction between ammonia and water, ammonium - (NH ₄ ⁺ ) and hydroxide ions (OH ^- ) are formed:

${\displaystyle \mathrm {NH_{3}+H_{2}O\rightleftharpoons NH_{4}^{+}+OH^{-}} }$.

The equilibrium is clearly to the left of the reaction. The base constant K _B

${\displaystyle K_{\mathrm {B} }={\frac {c\mathrm {[NH_{4}^{+}]} \cdot c\mathrm {[OH^{-}]} }{c\mathrm {[NH_{3}]} }}=1{,}75\cdot 10^{-5}}$

of ammonia is 1.75 · 10 ⁻⁵ (p K _B = 4.75). Ammonia is therefore only a moderately strong base . The degree of dissociation is very low. Depending on the concentration, this is only between 0.1% and 1%.

Equilibrium concentrations of dissolved ammonia and ammonium ions in ammonia water of various starting concentrations
Initial concentration in mol·l −1	0.1	0.5	1	2	5	10	15th
Equilibrium concentration (NH 3 ) in mol·l −1	0.099	0.497	0.996	1.994	4.991	9.987	14.984
Equilibrium concentration (NH 4 + ) in mol·l −1	0.001	0.003	0.004	0.006	0.009	0.013	0.016
Degree of protonation in mol%	1.3	0.59	0.42	0.30	0.19	0.13	0.11

use

Ammonia water is used as an additive in household cleaning agents (e.g. in glass cleaners) and to neutralize chlorine and formaldehyde after disinfection measures. In technology, for example, it is used to clean galvanized steel for subsequent painting (ammoniacal wetting agent washing).

It is used as an inexpensive alkaline solution in bleaching and dyeing works. It is used in food chemistry as an acidity regulator and is also used to break down milk protein, cocoa products and egg products. The food additive label is E 527.

In wood processing, ammonia water is used for a technique known as “smoking”: Tannin-containing woods such as oak, chestnut and robinia are exposed to ammonia vapor for a long time (half a day up to a week). The tannins in the wood react with the ammonia and trigger a color change to dark brown. Before access to industrial stains, new oak furniture was stored for some time above stables so that the ammonia vapor escaping from the animal dung stains the wood dark brown.

In the USA, ammonia water is used to kill germs, to obtain minced meat additive from slaughterhouse residues (disparagingly called pink slime ), and to extend the shelf life of meat products. In the EU, it is only approved for organic food in the manufacture of gelatine, as is the case in Switzerland. The use of ammonium hydroxide as an additive for coating agents for boiled eggs has been approved at Bio Suisse since the beginning of 2019 .

In the Kalina cycle , the lower boiling point , which depends on the mixing ratio of the ammonia water, is used to drive steam turbines with lower temperatures and the associated higher effect.

safety instructions

Ingestion of ammonia water causes severe pain , gastric catarrh , bloody vomiting , lung and voice damage , which are often fatal . It also attacks the eyes . Substantial amounts of ammonia can be released from ammonia water, which can cause serious damage to health if inhaled.

Individual evidence

1. ↑ ^{a b c d e f g} Entry on ammonia, aqueous solution in the GESTIS substance database of the IFA , accessed on August 27, 2016(JavaScript required) .
2. ↑ Entry on ammonia, aqueous solution in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on August 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
3. ↑ ^{a b} entry on ammonia. In: Römpp Online . Georg Thieme Verlag, accessed on June 13, 2014.
4. ↑ Ammonĭak . In: Meyers Großes Konversations-Lexikon . 6th edition. Volume 1, Bibliographisches Institut, Leipzig / Vienna 1905, pp.  443–445 . (there NH ₄ OH is called "ammonium hydroxide").
5. ↑ ammonium oxide hydrate . In: Lexicon of all technology , 2nd edition. 1904–1920 (there NH ₄ OH is called ammonium oxide hydrate).
6. ^ Lexicon of Chemistry . Spectrum Academic Publishing House, Heidelberg 2001.
7. ↑ Arnold Willmes: Pocket book chemical substances . Scientific publishing house Harri Deutsch, Frankfurt a. M., 2007, p. 101, ( limited preview in the Google book search).
8. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 91st – 100th, improved and greatly expanded edition. Walter de Gruyter, Berlin 1985, ISBN 3-11-007511-3 .
9. ↑ Smoking wood on the page Peters Holzmanufaktur by Peter Schirmer , accessed on July 7, 2018.
10. ↑ Philipp Löpfe: Pink-red meat slime . In: Tages-Anzeiger , April 7, 2012
11. ↑ Jim Avila: 70 Percent of Ground Beef at Supermarkets Contains 'Pink Slime' . ABC News. March 7, 2012. Accessed December 2015.
12. ↑ Regulation (EC) No. 889/2008 of the Commission of September 5, 2008 with implementing provisions for Regulation (EC) No. 834/2007 of the Council on organic production and the labeling of organic products with regard to organic Production, labeling and control.
13. ↑ This is new in organic farming 2019. (PDF; 277 KB) In: shop.fibl.org. Bio Suisse, 2018, accessed on February 1, 2019 .