Ammonia

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Ammonia
Ammonia.jpg
Names
IUPAC name
Azane
Other names
Hydrogen nitride
Nitrogen trihydride
Spirit of hartshorn
Trihydrogen nitride
Properties
NH3
Molar mass 17.031 g/mol
Appearance Colorless gas
Odor Pungent, suffocating
Density 0.86 kg/m3 (1.013 bar at b.p.)
0.769 kg/m3 (STP)
0.73 kg/m3 (1.013 bar at 15 °C)
681.9 kg/m3 (−33.3 °C) (liquid)
817 kg/m3 at −80 °C (transparent solid)
Melting point −77.73 °C (−107.91 °F; 195.42 K)
Boiling point −33.34 °C (−28.01 °F; 239.81 K)
47% w/w (0 °C)
38% w/w (15 °C)
34% w/w (20 °C)
31% w/w (25 °C)
28% w/w (30 °C)
18% w/w (50 °C)
Solubility Soluble in chloroform, diethyl ether, ethanol, methanol
Solubility in ethanol 20% w/w (0 °C)
10% w/w (25 °C)
Solubility in methanol 16% w/w (25 °C)
Vapor pressure 857.3 kPa
Acidity (pKa) 32.5 (−33 °C)
10.5 (DMSO)
Thermochemistry
193 J·mol−1·K−1
−46 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (anhydrous)
Lethal dose or concentration (LD, LC):
0.015 ml/kg (human, oral)
40,300 ppm (rat, 10 min)
28,595 ppm (rat, 20 min)
20,300 ppm (rat, 40 min)
11,590 ppm (rat, 1 hr)
7,338 ppm (rat, 1 hr)
4,837 ppm (mouse, 1 hr)
9,859 ppm (rabbit, 1 hr)
9,859 ppm (cat, 1 hr)
2,000 ppm (rat, 4 hr)
4,230 ppm (mouse, 1 hr)
Related compounds
Related compounds
Phosphine
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Ammonia is the simplest amine, with the formula NH3. It exists as a gas at room temperature, and dissolves in water as a weak base, with ammonium and hydroxide ions existing in solution. Several decades ago, it was considered that the solution of ammonia in water is a hydroxide of ammonium (NH4OH); currently it is known that ionic ammonium hydroxide is a minor tautomer of ammonia hydrate (NH3·H2O), with both coexisting in solution, but the non-ionic hydrate predominating. It is also a mild reducing agent, and is a common precursor to organic and inorganic amines, as well as other nitrogenous compounds such as hydrazine.

Properties

Physical

Ammonia is a colorless gas with a strong, pungent odor, sometimes described as being similar to rotting fish. It is highly soluble in water. Ammonia solution, particularly when concentrated, can dissolve many otherwise insoluble bases, or enhance their solubility. It dissolves copper(II) hydroxide, copper(II) oxychloride, and Chevreul's salt, to form the tetraammine copper(II) complex, and works similarly with other transition metal compounds such as those of nickel, chromium, and cobalt.

Chemical

Ammonia slightly dissociates in solution to form ammonium and hydroxide ions, making it a weak Brønsted-Lowry base.

NH3 + H2O → NH4+ + OH-

Ammonia is commonly used to produce organic and inorganic amines.

Availability

Aqueous ammonia solutions can be purchased in many stores as household cleaners; these solutions release gaseous ammonia on heating. These solutions are generally 3%-10% but solutions of 30% ammonia are possible and only sold through chemical supply companies. One problem with hardware store ammonia is that it usually contains surfactants which are difficult to remove. In some reactions these do not present any problems, but oftentimes they do.

Chemist-approved brands

Approved brands of ammonia ideally lack surfactants or other additives, or have very low amounts of them. Buying the cheapest brands of ammonia is recommended, as the extra money goes towards the additives which cause more problems. Certain drug stores may have pure ammonia solutions.

United States

  • Ace (Ace)
  • Blue Ribbon (True Value)

Purification of aqueous ammonia

Ammonia solutions that contain surfactants can be purified by heating them and trapping the evolving ammonia with a funnel-and-beaker trap, which is a device typically used to dissolve highly soluble gases in water and prevent water from rushing back into the heating flask. A pure, surfactant free solution of ammonia forms in the trap.

Anhydrous ammonia is sold as compressed gas in cylinders, though they are generally available only to industrial entities.

Preparation

Ammonia gas can be generated in the lab by adding a solution of an ammonium salt, such as ammonium nitrate to another solution of sodium hydroxide or another base such as sodium carbonate. Completion of the reaction may require heating in the case of the latter. The two are reacted in a gas generator and the ammonia gas produced can be channeled into cold water to dissolve it. If the amounts are carefully regulated, this can be a method for producing relatively cheap and pure sodium nitrate, typically a preferable nitrate to the ammonium salt, as a byproduct.

If sodium carbonate is used instead of sodium hydroxide, ammonium carbonate will be formed as a precipitate within any tubing or solutions the ammonia gases are channeled through, so in order to make aqueous ammonia for use as a reagent, only sodium hydroxide can be used.

Ammonia can also be generated by heating ammonium bicarbonate, which yields ammonia gas, carbon dioxide and water vapor. Bubbling the resulting gas through a scrubber will remove the carbon dioxide, leaving only ammonia.

Thermal decomposition of urea will give ammonia, best in the presence of a base like calcium hydroxide.

Projects

Handling

Safety and toxicity

Ammonia is known for presenting itself with an intensely pungent odor. The smell of ammonia is a good warning as to when the concentration in air is beginning to increase to unsafe levels. Inhalation of strong ammonia fumes may cause a powerful physiological response that increases heart and breathing rates and creates a very strong feeling of wakefulness. This is the same response seen when one is woken using smelling salts. This is a safe practice if only done very occasionally.

Ammonia is an incredibly powerful decongestant, but its use as such is not recommended.

Ammonia solution and gas, but especially the anhydrous gas, can produce mild to moderate burns on the skin depending on concentration and duration. Contact of the skin with the gas often manifests as a very cold sensation.

Legal issues

Ammonia is sometimes used in the clandestine manufacture of illegal drugs, and may add to suspicion of such activities if found by law enforcement. In addition, any foul odor, such as that of ammonia, is likely to be noticed by neighbors in a densely populated area if it is not kept under control.

Ammonia, however, is readily available and not highly restricted in most countries.

Storage

Aqueous ammonia solutions should be kept in well ventilated, cold dark places. Anhydrous ammonia tanks should be kept away from any heat source, in well ventilated areas, and be inspected periodically.

Disposal

Although ammonia can be released in open air, due to it's strong smell, a good idea would be to neutralize it first with an acid, any acid can do the trick, preferably cheap ones, such as acetic acid or vinegar. Volatile acids however may generate a thick fog of ammonia salts, which are notorious for their persistence. Ammonia salts in general are good fertilizers, so they can be safely poured in the soil.

References

Relevant Sciencemadness threads