Ammonia solution, also known as ammonia water, ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or (inaccurately) ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although the name ammonium hydroxide suggests a salt with the chemical formula , it is impossible to isolate samples of NH4OH. The ions and OH− do not account for a significant fraction of the total amount of ammonia except in extremely dilute solutions.
The concentration of such solutions is measured in units of the Baumé scale (density), with 26 degrees Baumé (about 30% of ammonia by weight at ) being the typical high-concentration commercial product.
Basicity of ammonia in water
In aqueous solution, ammonia
deprotonation a small fraction of the water to give
ammonium and
hydroxide according to the following equilibrium:
- NH3 + H2O ⇌ + OH−.
In a 1 M
ammonia solution, about 0.42% of the ammonia is converted to ammonium, equivalent to pH = 11.63
because = 0.0042 M, OH
− = 0.0042 M, NH
3 = 0.9958 M, and pH = 14 + log
10OH
− = 11.62. The base ionization constant is
- Kb = = 1.77.
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 , the density of a saturated solution is 0.88 g/ml; it contains 35.6% ammonia by mass, 308 grams of ammonia per litre of solution, and has a molarity of approximately 18 mol/L. At higher temperatures, the molarity of the saturated solution decreases and the density increases.
Upon warming of saturated solutions, ammonia gas is released.
Applications
In contrast to anhydrous ammonia, aqueous ammonia finds few non-niche uses outside of
.
Cleaning products
Ammonia solutions are used as cleaning products for many surfaces and applications. Ammonia in water is sold as a cleaning agent by itself, usually labeled as simply "ammonia", as well as in cleaning products combined with other ingredients. It may be sold plain, lemon-scented (and typically colored yellow), or pine-scented (green). Commonly available ammonia with soap added is known as "cloudy ammonia".
Household ammonia ranges in concentration by weight from 5% to 10% ammonia.
More concentrated solutions (higher than 10%) are used for in professional and industrial cleaning products.
US manufacturers of cleaning products are required to provide the product's material safety data sheet that lists the concentration used.
Alkyl amine precursor
In industry, aqueous ammonia can be 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.
Absorption refrigeration
In the early years of the twentieth century, the vapor absorption cycle using water-ammonia systems was popular and widely used, but after the development of the vapor compression cycle it lost much of its importance because of its low coefficient of performance (about one fifth of that of the vapor compression cycle). Both the Electrolux refrigerator
[ Vapour Absorption Cycle - Domestic Electrolux Refrigerator] and the Einstein refrigerator are well known examples of this application of the ammonia solution.
Water treatment
Ammonia is used to produce
monochloramine, which may be utilised as a disinfectant.
In drinking water, chloramine is preferred over direct chlorination for its ability to remain active in stagnant water pipes longer, thereby reducing the risk of waterborne infections.
Ammonia is used by Fishkeeping for the purposes of setting up a new fish tank using an ammonia process called fishless cycling.
Food production
Baking ammonia (ammonium carbonate and ammonium bicarbonate) was one of the original chemical
. It was obtained from deer antlers.
It is useful as a leavening agent, because ammonium carbonate is heat activated. This characteristic allows bakers to avoid both yeast's long proofing time and the quick
Carbon dioxide dissipation of baking soda in making breads and cookies rise. It is still used to make
and other crisp baked goods, but its popularity has waned because of ammonia's off-putting smell and concerns over its use as a food ingredient compared to modern-day baking powder formulations. It has been assigned
E number E527 for use as a food additive in the
European Union.
Aqueous ammonia is used as an acidity regulator to bring down the acid levels in food. It is classified in the United States by the Food and Drug Administration as generally recognized as safe (GRAS) when using the food grade version.[ Database of Select Committee on GRAS Substances (SCOGS) Reviews: Ammonium hydroxide, U.S. Food and Drug Administration] Its pH control abilities make it an effective antimicrobial agent.
Furniture darkening
In furniture-making,
ammonia fuming was traditionally used to darken or stain wood containing
tannic acid. After being sealed inside a container with the wood, fumes from the ammonia solution react with the tannic acid and iron salts naturally found in wood, creating a rich, dark stained look to the wood. This technique 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.
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 oxide residues, such as those formed from Tollens' reagent. It is often found in solutions used to clean gold, silver, and platinum jewelry, but may have adverse effects on porous gem stones like opals and pearls.
[The Jeweler's Bench. 2015. Fine Jewelry Cleaner. Littleton, Colo.]
See also
Further reading
External links
