Physical Properties of Ammonia
- Colourless gas with pungent choking smell
- Alkaline gas (turns damp red limus paper blue)
- Less dense than air
- Very soluble in water
Tests For Ammonia
You can test for the presence of ammonia with the two tests below:
Test 1
Hold a damp red limus paper into unknown gas. If the litmus paper turns blue, then the gas is ammonia.
This is because ammonia gas dissolves into water forming ammonium hydroxide solution which dissociates into ammonium ions and hydroxide ions. The hydroxide ions causes solution to become basic.
$$\text{NH}_{3}(\text{g})+\text{H}_{2}\text{O}(\text{l}) \rightarrow \text{NH}_{4}\text{OH}(\text{aq}) \rightleftharpoons \text{NH}_{4}^{+} (\text{aq}) + \text{OH}^{-}(\text{aq})$$
Test 2
Dip a glass rod in concentrated hydrochloric acid and then insert it in the unknown gas. Dense white fumes are formed if the gas is ammonia.
$$\text{NH}_{3}(\text{g}) + \text{HCl}(\text{aq}) \rightarrow \text{NH}_{4}\text{Cl}(\text{s})$$
Uses of Ammonia
Ammonia is used to make:
- fertilisers (nitrogeneous fertilisers – ammonium nitrate, ammonium sulphate)
- nitric acid
- explosive
- nylon
Other Notes
Ammonium nitrate is made by reacting ammonia with nitric acid
$$\text{NH}_{3}(\text{aq})+\text{HNO}_{3}(\text{aq}) \rightarrow \text{NH}_{4}\text{NO}_{3}(\text{aq})$$
Ammonium sulphate is made by reacting ammonia with sulphuric acid
$$2 \text{NH}_{3}(\text{aq}) + \text{H}_{2}\text{SO}_{4}(\text{aq}) \rightarrow (\text{NH}_{4})_{2}\text{SO}_{4}(\text{aq})$$
Properties of Ammonium Salts
- White or colourless solid
- Soluble in water
Tests for Ammonium Salts
You can test for the presence of ammonium salts with the test below:
Heat the unknown substance with aqueous sodium hydroxide. If ammonia gas is produced, the unknown substance is an ammonium salt.
Use the tests above to verify the presence of ammonia gas.
Preparation of Ammonium Salts
Ammonium salts can be prepared by using dilute acid and ammonium hydroxide or carbonate.
$$\text{H}_{2}\text{SO}_{4}(\text{aq}) + 2 \text{NH}_{4}\text{OH}(\text{aq}) \rightarrow (\text{NH}_{4})_{2}\text{SO}_{4}(\text{aq}) + 2\text{H}_{2}\text{O}(\text{l})$$
$$\text{H}_{2}\text{SO}_{4}(\text{aq}) + (\text{NH}_{4})_{2}\text{CO}_{3}(\text{aq}) \rightarrow (\text{NH}_{4})_{2}\text{SO}_{4}(\text{aq}) + \text{H}_{2}\text{O}(\text{l}) + \text{CO}_{2}(\text{g})$$
