Ammonia

 

Ammonia

Chemical formula	NH3
OTP appearance	colorless, noxious gas
Molar Mass(g/mol)	17
Density(g/cc)	0.00073
Melting Point(°C)	-77.7
Boiling Point(°C)	-33.3
Solubility in water(g/L)	310 (18.25M)
NFPA 704	1 3 0

Ammonia is a key industrial chemical. It is energetically expensive to synthesize chemically, but some biological processes produce it in small amounts.

Uses

Primary

• Key industrial chemical
  • feedstock for Ostwald process production of nitric acid
  • feedstock for electrochemical oxidation to nitrates
  • precursor to all ammonium compounds

Secondary

• Antimicrobial: With a pH much higher than a neutral water solution, it denatures proteins and some other organics, leading to cell damage and eventually death of the organism.
• Cleanser: Ammonia brings fats and oils into aqueous solution, making it an efficient cleanser for many types of dirt. The remaining water, containing ammonia, will evaporate leaving no wetness behind.
• Fertilizer/Soil treatment: raises the nitrogen value and the pH of soil when used as a fertilizer
• feedstock for nitrates via ammonia biofiltration

Natural occurrence

• Ammonia is produced by fish, who excrete it in lieu of urine
• Ammonia is produced by environmental bacteria acting on urine

Hazards

Ammonia is toxic. Annhydrous ammonia can kill you with a single lungfull. Treat both with care.

Production

Synthesis

Alkaline Decomposition of Urea

1. Dissolve 15 ubm urea in a minimum amount of water
2. Slowly combine with an equimolar amount (~18ubm) calcium oxide

   NB: Keep temp below 133°C to prevent urea decomposition (producing carbon dioxide or ammonium carbonate

   Lead outgases to bubble through distilled water to absorb the ammonia

   CO(NH₂)₂ + Ca(OH)₂ → CaCO₃ + 2 NH₃

3. Filter
4. Discard residue. It is calcium carbonate
5. Heat filtrate, possibly adding more calcium oxide, to expel as much ammonia as possible into the bubbler.

Haber process

Main article Haber process

The haber process is a direct (catalyzed) synthesis of ammonia from hydrogen and nitrogen gases.

3 H₂ + N₂

{Fe₃O₄

→

heat}

2 NH₃

Cyanamide process

Massively inefficient and only available after electrolysis, this process is unlikely to be used.

1. Produce calcium carbide with an arc furnace

   Ca + 2 C

   {

   →

   2000°C}

   CaC₂

2. Flow nitrogen gas over the -carbide at 1000°C producing calcium cyanamide.

   CaC₂ + N₂

   {

   →

   1000°C, 1 atm}

   CaCN₂ + C

3. Combine -cyanamide with water producing ammonia.

   CaCN₂ + 3 H₂O

   {

   →

   OTP}

   CaCO₃ + 2 NH₃

Serpek process

1. Expose magnesium to nitrogen in a hot environment, producing magnesium nitride.

   3 Mg + N₂

   {

   →

   800°C}

   Mg₃N₂

2. Immerse magnesium nitride in water, producing ammonia.

   Mg₃N₂ + 6 H₂O → 3 Mg(OH)₂ + 2 NH₃

Purification

Concentration

Main article ammonium hydroxide

Concentration by conversion

Many ammonium salts can be thermally decomposed. Convert dilute ammonia to something else such as ammonium chloride or ammonium (bi)carbonate, then decompose that, diferentially absorbing the ammonia and the other material.

1. Add equimolar amounts of hydrochloric acid and ammonia in solution, producing ammonium chloride.
2. Boil dilute ammonium chloride to concentrate
3. Add sodium hydroxide to solution producing ammonia and salt (and more water)

See Also

• urease