Ammonium hydroxide

Main article: Ammonia

Ammonium hydroxide

Ball-and-stick model of the ammonia molecule
Identifiers
CAS Number	1336-21-6 Y
ChEBI	CHEBI:18219 Y
ChemSpider	14218 Y
Jmol 3D model	Interactive image
KEGG	C01358 N
UNII	5138Q19F1X Y
InChI InChI=1S/H3N.H2O/h1H3;1H2 Y Key: VHUUQVKOLVNVRT-UHFFFAOYSA-N Y InChI=1/H3N.H2O/h1H3;1H2 Key: VHUUQVKOLVNVRT-UHFFFAOYAI
SMILES [OH-].[NH4+]
Properties
Chemical formula	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)
Solubility in water	Miscible
Thermochemistry
Std molar entropy (So298)	111 J·mol−1·K−1
Std enthalpy of formation (ΔfHo298)	−80 kJ·mol−1
Vapor pressure	{{{value}}}
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 verify (what is YN ?)
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.

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

K_b = [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.

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.

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). 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".

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.

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 that formed from 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.

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

• Common chemicals
• Conjugate acid

External links

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