1. General Information and Introduction
- Formula and Molecular Mass: The chemical formula for ammonia is NH3โ. Its molecular mass is approximately 17 g/mol.
- Nature: It is a colorless gas with a pungent, characteristic smell. It is a covalent molecule with a pyramidal shape due to the presence of a lone pair of electrons on the nitrogen atom.
- Physical Properties: Ammonia gas is lighter than air and is extremely soluble in water, forming ammonium hydroxide (NH4โOH), a weak base.
2. Laboratory Preparation of Ammonia
- Reactants: Ammonia is prepared in the lab by heating an ammonium salt, such as ammonium chloride (NH4โCl), with a strong alkali like calcium hydroxide (Ca(OH)2โ).
- Reaction: 2NH4โCl+Ca(OH)2โฮ
โCaCl2โ+2H2โO+2NH3โ
- Drying and Collection: The ammonia gas is dried by passing it through quicklime (CaO). Drying agents like concentrated sulfuric acid or calcium chloride are not used because they would react with the ammonia. The gas is collected by the downward displacement of air because it is lighter than air and is very soluble in water.
3. The Fountain Experiment
This is a classic experiment used to demonstrate two key properties of ammonia gas:
- High solubility in water: As the gas dissolves rapidly in the flask, it creates a partial vacuum.
- Basic nature: The red litmus solution from the beaker is forced into the flask by atmospheric pressure, where it turns blue, confirming the basic nature of the resulting ammonium hydroxide solution.
4. Industrial Manufacturing: The Haber Process
The Haber process is the main industrial method for producing ammonia from its constituent elements.
- Reaction: It involves the direct combination of nitrogen gas (N2โ) and hydrogen gas (H2โ) in a reversible reaction. N2โ+3H2โโ2NH3โ+Heat
- Conditions: The reaction is carried out at a high pressure (around 200 atmospheres) and a moderate temperature (450ยฐC-500ยฐC) in the presence of an iron catalyst with molybdenum as a promoter.
5. Chemical Properties
- Basic Nature: Ammonia dissolves in water to form ammonium hydroxide, which is a weak base. NH3โ+H2โOโNH4โOHโNH4+โ+OHโ This solution turns red litmus paper blue and reacts with acids to form ammonium salts.
- Reaction with Metal Salts: Ammonium hydroxide reacts with solutions of certain metal salts to precipitate the corresponding metal hydroxides. This reaction is used to identify metal ions like iron, copper, and zinc.
- Reducing Agent: Ammonia can act as a reducing agent when heated. For example, it reduces copper(II) oxide to copper. 3CuO+2NH3โ=
โ3Cu+3H2โO+N2โ
6. Uses of Ammonia
- Fertilizers: A major use is in the production of nitrogenous fertilizers like urea, ammonium sulfate, and ammonium nitrate.
- Explosives: It is used in the manufacture of explosives like ammonium nitrate.
- Refrigerant: Liquid ammonia is used as a refrigerant in large-scale cold storage plants due to its high latent heat of vaporization.
- Chemicals: Used to produce other chemicals like nitric acid and sodium carbonate.
7. Test for Ammonia ๐งช
The most common and reliable test for ammonia gas is its reaction with hydrogen chloride gas.
- When a glass rod dipped in concentrated hydrochloric acid is brought near the mouth of a test tube containing ammonia gas, dense white fumes of ammonium chloride are produced.NH3โ(g)+HCl(g)โNH4โCl(s)
Ammonia also has a characteristic pungent smell and turns moist red litmus paper blue, but the fumes test is considered definitive.
8. Reactions of Ammonia
Ammonia (NH3โ) is a versatile chemical that can act as a base, a reducing agent, and a fuel depending on the conditions.
Reaction with Oxygen
- Without a catalyst: When ammonia burns in an excess of oxygen, it produces nitrogen gas and water vapor, with the release of a significant amount of heat. This reaction is often used to get rid of ammonia waste.4NH3โ+3O2โโ2N2โ+6H2โO+Heat
- With a catalyst: In the presence of a platinum catalyst and at a high temperature (around 800ยฐC), ammonia is catalytically oxidized to form nitric oxide and water. This is the first step of the Ostwald process for manufacturing nitric acid.4NH3โ+5O2โ=Cโ4NO+6H2โO
Reaction with Chlorine
Ammonia reacts with chlorine gas in two different ways, depending on the relative amounts of the reactants.
- Excess Ammonia: When ammonia is in excess, it reacts with chlorine to produce nitrogen gas and ammonium chloride.8NH3โ+3Cl2โโN2โ+6NH4โClThe ammonium chloride is observed as dense white fumes.
- Excess Chlorine: If chlorine is in excess, it reacts with ammonia to produce nitrogen trichloride (NCl3โ), a highly explosive and volatile liquid, and hydrogen chloride gas.NH3โ+3Cl2โโNCl3โ+3HCl
