Ammonium hydroxide

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Ammonium hydroxide
Ball-and-stick model of the ammonia molecule Ball-and-stick model of the water molecule
Ball-and-stick model of the ammonium cation Ball-and-stick model of the hydroxide anion
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 Colorless liquid
Odor "Fishy", highly pungent
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
Thermochemistry
Std molar
entropy
So298
111 J·mol−1·K−1[2]
Std enthalpy of
formation
ΔfHo298
−80 kJ·mol−1[2]
Hazards[3]
EU classification Dangerous for the Environment (Nature) N Corrosive C
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
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
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 an alkali with composition [NH4+][OH], it is actually impossible to isolate samples of NH4OH, as these ions do not comprise a significant fraction of the total amount of ammonia except in extremely dilute solutions.[4]

Basicity of ammonia in water[edit]

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[edit]

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.

Application[edit]

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 labeled as simply "ammonia". It may be sold plain, lemon-scented (and typically colored yellow), or pine-scented (green). Commonly available ammonia that has had soap added to it is known as "Cloudy ammonia".

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.[5]

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.[6]

In food production, ammonium hydroxide is used as a leavening agent or acidity regulator and is classified by the Food and Drug Administration as generally recognized as safe (GRAS).[7] Its pH control abilities make it an effective antimicrobial agent.

Ammonium hydroxide is used in the Tobacco Industry as well. According to Phillip Morris USA, quantities up to 0.3 (% in Tobacco) ammonium hydroxide are used for "flavor" enhancement and as a "processing aid".[8]

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.

Ammonium hydroxide is used to treat straw, produce "ammoniated straw" making it more edible for cattle.[9]

Laboratory use[edit]

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 oxide 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[edit]

References[edit]

  1. ^ Record of Ammonia solution in the GESTIS Substance Database from the IFA
  2. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22. ISBN 0-618-94690-X. 
  3. ^ Ammónium-hidroxid (ESIS)[dead link]
  4. ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 187. ISBN 978-0130399137. 
  5. ^ Eller, Karsten; Henkes, Erhard; Rossbacher, Roland; Höke, Hartmut (2000). "Amines, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a02_001. ISBN 978-3-527-30673-2. 
  6. ^ Rigers, Shayne; Umney, Nick. "Acidic and alkaline stains". Wood Coatings: Theory and Practice. Amsterdam: Elsevier. pp. 618–9. ISBN 978-0-444-52840-7. 
  7. ^ Database of Select Committee on GRAS Substances (SCOGS) Reviews: Ammonium hydroxide, U.S. Food and Drug Administration
  8. ^ http://www.philipmorrisusa.com/en/cms/Products/Cigarettes/Ingredients/Tobacco_Flavor_Ingredients/default.aspx?src=top_nav
  9. ^ http://ohioline.osu.edu/agf-fact/0015.html

Further reading[edit]

External links[edit]