Ammonium hydroxide

Main article: Ammonia

Ammonium hydroxide
Identifiers
CAS number	1336-21-6 Y
ChemSpider	14218 Y
UNII	5138Q19F1X Y
KEGG	C01358 N
ChEBI	CHEBI:18219 Y
Jmol-3D images	Image 1
SMILES [OH-].[NH4+]
InChI InChI=1S/H3N.H2O/h1H3;1H2 Y Key: VHUUQVKOLVNVRT-UHFFFAOYSA-N Y InChI=1/H3N.H2O/h1H3;1H2 Key: VHUUQVKOLVNVRT-UHFFFAOYAI
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: Y/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]

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.

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

• Common chemicals
• Conjugate acid
• Windex

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