Ammonium hydroxide

Ammonium hydroxide
Ammonium hydroxide
Identifiers
CAS number 1336-21-6 YesY
ChemSpider 14218 YesY
UNII 5138Q19F1X YesY
KEGG C01358 N
ChEBI CHEBI:18219 YesY
Jmol-3D images Image 1
Properties[1]
Molecular formula NH4OH
Molar mass 35.04 g/mol
Appearance very volatile solution, colorless, bitter smell
Density 0.91 g/cm3 (25 %)
0.88 g/cm3 (32 %)
Melting point

−57.5 °C (25%)
−91.5 °C (32%)

Boiling point

37.7 °C (25%)
24.7 °C (32%)

Solubility in water Miscible
Hazards[2]
EU classification Corrosive (C)
Dangerous to the environment (N)
R-phrases R34, R50
S-phrases (S1/2), S26, S36/37/39, S45, S61
Related compounds
Other anions Ammonium chloride
Ammonium cyanide
Other cations Tetramethylammonium hydroxide
Related compounds Ammonia
Hydroxylamine
 N hydroxide (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Ammonia solution, also known as ammonium hydroxide, ammonia water, ammonical liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or simply ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although the name ammonium hydroxide suggests a base with composition [NH4+][OH], it is actually impossible to isolate samples of NH4OH, as these ions only comprise a significant fraction of the total amount of ammonia in extremely dilute solutions.[3]

Contents

Basicity of ammonia in water

In aqueous solution, ammonia deprotonates a small fraction of the water to give ammonium and hydroxide according to the following equilibrium:

NH3 + H2O is in equilibrium with NH4+ + OH.

In a 1M ammonia solution, about 0.42% of the ammonia is converted to ammonium, equivalent to a pH of 11.63. The base ionization constant is

Kb = [NH4+][OH-]/[NH3] = 1.8×10−5

Saturated solutions

Like other gases, ammonia exhibits decreasing solubility in solvent liquids as the temperature of the solvent increases. Ammonia solutions decrease in density as the concentration of dissolved ammonia increases. At 15.6 °C (60.1 °F), the density of a saturated solution is 0.88 g/ml and contains 35% ammonia by mass, 308 g/l w/v, (308 grams of ammonia per litre of solution) and has a molarity of approximately 18 mol L−1. At higher temperatures, the molarity of the saturated solution decreases and the density increases.

When solutions that are saturated at cold temperatures are sealed in containers and subsequently warmed, the concentration of the solution decreases and the vapor pressure of ammonia gas increases. Unsealing such containers can lead to a burst of ammonia gas. In extreme cases, the containers could rupture.

From a chemist's perspective, one should be aware that the concentration of a saturated solution is continually dropping as the container is handled in a warmer environment. Thus, old samples of ammonium hydroxide will deviate from 18 M, as can be verified by titration.

Applications

Household ammonia is dilute ammonium hydroxide, which is also an ingredient of numerous other cleaning agents, including many window cleaning formulas. In addition to use as an ingredient in cleansers with other cleansing ingredients, ammonium hydroxide in water is also sold as a cleaning agent by itself, usually labelled as simply "ammonia". It may be sold plain, lemon-scented (and typically colored yellow), or pine-scented (green).

In industry, ammonium hydroxide is used as a precursor to some alkyl amines, although anhydrous ammonia is usually preferred. Hexamethylenetetramine forms readily from aqueous ammonia and formaldehyde. Ethylenediamine forms from 1,2-dichloroethane and aqueous ammonia.[4]

In furniture-making, ammonium hydroxide was traditionally used to darken or stain wood containing tannic acid. After being sealed inside a container with the wood, fumes from the ammonium hydroxide react with the tannic acid and iron salts naturally found in wood, creating a rich, dark stained look to the wood. This was commonly used during the arts and crafts movement in furniture- a furniture style which was primarily constructed of oak and stained using these methods. [5]

Ammonium hydroxide is also used in the meat packing industry. Some companies treat their beef "with a pH enhancement process that forms ammonium hydroxide in the finished product."

It is also known to be used by aquarists for the purposes of fishless cycling, but this requires that there are no surfactants or scents, it should be colorless and shouldn't foam when shaken up.

Laboratory use

Aqueous ammonia is used in traditional qualitative inorganic analysis as a complexant and base. Like many amines, it gives a deep blue coloration with copper(II) solutions. Ammonia solution can dissolve silver residues, such as that formed from Tollens' reagent.

When ammonium hydroxide is mixed with dilute hydrogen peroxide in the presence of a metal ion, such as Cu2+, the peroxide will undergo rapid decomposition.

See also

References

  1. ^ Record of Ammonia solution in the GESTIS Substance Database from the IFA
  2. ^ Ammónium-hidroxid (ESIS)[dead link]
  3. ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 187. ISBN 978-0130399137. 
  4. ^ Karsten Eller, Erhard Henkes, Roland Rossbacher, Hartmut Höke "Amines, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a02_001
  5. ^ Conservation of Furniture

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Look at other dictionaries:

  • ammonium hydroxide — n a weakly basic compound NH4OH that is formed when ammonia dissolves in water and that exists only in solution …   Medical dictionary

  • ammonium hydroxide — n. a weak, colorless base, NH4OH, formed by dissolving ammonia in water …   English World dictionary

  • ammonium hydroxide — Chem. a basic compound, NH4OH, existing only in solution, formed by dissolving ammonia gas in water. Cf. ammonia. [1900 05] * * * ▪ chemical compound also called  Aqua Ammonia,         solution of ammonia gas in water, a common commercial form of …   Universalium

  • ammonium hydroxide — noun a water solution of ammonia • Syn: ↑ammonia water, ↑ammonia • Derivationally related forms: ↑ammoniate (for: ↑ammonia) • Hypernyms: ↑liquid …   Useful english dictionary

  • ammonium hydroxide — noun Date: 1899 a weakly basic compound NH4OH that is formed when ammonia dissolves in water and that exists only in solution …   New Collegiate Dictionary

  • ammonium hydroxide — noun The ionic base, NHOH, obtained by dissolving ammonia in water. Syn: E527, acidity regulator …   Wiktionary

  • ammonium hydroxide — UK [əˌməʊnɪəm haɪˈdrɒksaɪd] / US [əˌmoʊnɪəm haɪˈdrɑksaɪd] noun [uncountable] chemistry a strong alkali that is a liquid consisting of ammonia and water …   English dictionary

  • ammonium hydroxide — ammo′nium hydrox′ide n. chem. a basic liquid compound, NH4OH; ammonia water • Etymology: 1900–05 …   From formal English to slang

  • ammonium hydroxide — /əˌmoʊniəm haɪˈdrɒksaɪd/ (say uh.mohneeuhm huy droksuyd) noun a basic solution of ammonia in water, used extensively in domestic cleaning agents …  

  • Ammonium cyanide — Ammonium cyanide …   Wikipedia

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