How To Make Anhydrous Ammonia
As anhydrous ammonia is used as a solvent in inorganic chemistry, it becomes important to know how to make anhydrous ammonia. Most of the chemical reactions require a suitable solvent. Water is the mostly used solvent in inorganic Chemistry. Organic solvents are used in organic chemistry. The use of water has many advantages, but the use of solvents other than water developed due to following reasons.
• Reactions involving strong reducing agents cannot be carried out in the water, since water can be reduced, and thus resulting in the evolution of hydrogen.
• Water can hydrolyze some compounds.
• Reactions at high temperatures (>100 °C) cannot be carried out unless if there is a special equipment.
Ammonia is one of the most widely used non-aqueous solvents and it is called anhydrous ammonia. It has a high boiling point and it boils below room temperature.
Property | Ammonia | Water |
Melting point Boiling point Heat of fusion/ kJ mol-1 Heat of vaporization/ kJ mol-1 Density / kg m-3 | 195.41 239.80 5.66 23.35 667 @ 240.15 K | 273.15 373.15 6.00 40.72 960 @ 373.15 K |
Making Anhydrous Ammonia
Ammonia irritates the respiratory tracts. Therefore, preparation and work with ammonia should be carried out in a fume cupboard.
Method 1:
- Prepare a mixture of 1-2 g of ammonium chloride and 1-2 g of slaked lime (Calcium hydroxide- Ca(OH)2 ).
- Transfer the mixture into a test tube and close it with a stopper accommodating a bent-gas discharge tube.
- Heat the test tube with the mixture.
- Bring a piece of litmus paper wetted with concentrated hydrochloric acid to the end of the gas-discharge tube.
Method 2:
Procedure:
• First, place ammonium chloride / water solution in a flask and chill to 0 0C using ice/salt bath.
• Then add an equinormal amount of sodium chloride to convert ammonium chloride into ammonia salt. (Enough amount of water should be added to make the concentration of ammonia less than 40%. Because it saturates around 47% at 0 0C)
• Next, gently boil the content in the flask to liberate ammonia as a gas. The water vapour which produces in the process comes along and condenses back into the flask. The boiling process continues until no more ammonia is liberated.
When the liberating of the ammonia gas is over, the boiling flask can be recharged for the next distillation.
• Immediately use the collected ammonia by disconnecting from the set up and then perform the reaction requiring liquid ammonia in situ (Eg: Birch reduction).
• The collected ammonia is anhydrous and any water in the condenser can be removed a CaO dryer. It can be further removed by forming ice on contact with the cold finger.
How To Make Anhydrous Ammonia – Summary
Anhydrous ammonia is a colourless gas with a characteristic pungent odor. It is a corrosive gas and very soluble in water. Anhydrous ammonia is a widely used non- aqueous solvent. There are several methods available for the small scale production of anhydrous ammonia. In large-scale production, it is produced by using hydrogen and nitrogen at a very high temperature and pressure.
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