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Ammonium hydroxide

 

Ammonium hydroxide

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
 Y
ChEBI  Y
ChemSpider  Y
Jmol-3D images Image
KEGG  N
UNII  Y
Properties[1]
NH5O
Molar mass 35.04 g/mol
Appearance Colourless liquid
Odor "Fishy", highly pungent
Density 0.91 g/cm3 (25 % w/w)
0.88 g/cm3 (35 % w/w)
Melting point −57.5 °C (−71.5 °F; 215.7 K) (25% w/w)
−91.5 °C (35% w/w)
Boiling point 37.7 °C (99.9 °F; 310.8 K) (25% w/w)
24.7 °C (35% w/w)
Miscible
Thermochemistry
111 J·mol−1·K−1[2]
−80 kJ·mol−1[2]
Hazards[3]
Dangerous for the Environment (Nature) N Corrosive C
R-phrases 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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 N  (: Y/N?)

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]

Contents

  • Basicity of ammonia in water 1
  • Saturated solutions 2
  • Application 3
  • Laboratory use 4
  • See also 5
  • References 6
  • Further reading 7
  • External links 8

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 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.

Application

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% ammonium hydroxide are used in tobacco 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, producing "ammoniated straw" making it more edible for cattle.[9]

Laboratory use

Aqueous ammonia is used in traditional Tollens' reagent. It is often found in solutions used to clean gold, silver, and platinum jewelry, but may have negative effects on porous gem stones like opals and pearls. [10]

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. ^ Ammonia solutionRecord of in the GESTIS Substance Database of the IFA
  2. ^ a b Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A22.  
  3. ^ Ammónium-hidroxid (ESIS)
  4. ^ Housecroft, C. E.; Sharpe, A. G. (2004). Inorganic Chemistry (2nd ed.). Prentice Hall. p. 187.  
  5. ^ Eller, Karsten; Henkes, Erhard; Rossbacher, Roland; Höke, Hartmut (2000). "Amines, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry.  
  6. ^ Rigers, Shayne; Umney, Nick. "Acidic and alkaline stains". Wood Coatings: Theory and Practice. Amsterdam: Elsevier. pp. 618–9.  
  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
  10. ^ The Jeweler's Bench. 2015. Fine Jewelry Cleaner. Littleton, CO.

Further reading

  • Geornaras, I.; Sofos, J. N. (2005). "Combining physical and chemical decontamination interventions for meat". In Sofos, John Nikolaos. Improving the safety of fresh meat. Boca Raton: CRC Press. pp. 433–60.  
  • Skandamis, Panagiotis N.; Nychas, George-John E.; Sofos, John N. (2010). "Meat Decontamination". In Toldrá, Fidel. Handbook of Meat Processing. Ames: Iowa State University Press. pp. 43–85.  
  • Edwards, Jessica Renee; Fung, Daniel Y.C. (2006). "Prevention and Decontamination of Escherichia Coli O157:h7 on Raw Beef Carcasses in Commercial Beef Abattoirs". Journal of Rapid Methods and Automation in Microbiology 14 (1): 1–95.  

External links

  • External Material Safety Data Sheet – for ammonium hydroxide (10%-35% solution).
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