Nitrogen exists as a diatomic molecule, N2
Physical properties of nitrogen
- It is colourless
- It is odorless
- It does not burn and does not support burning except magnesium which burns with it.
Chemically, nitrogen gas is very unreactive due to the strong bonds between the nitrogen atoms in the molecule However, under forced conditions; nitrogen reacts with hydrogen gas to form ammonia in the presence of the iron catalyst
Manufacture of nitrogen gas
Nitrogen gas is manufactured by fractional distillation of liquid air
Uses of nitrogen
- It is used in the manufacture of ammonia
- It is used to provide an inert atmosphere during the arc welding of aircraft parts and in electric bulbs
The need for nitrogen, phosphorus and potassium compounds in plant life
Nitrogen is essential in the manufacture of proteins while phosphorus is mainly needed for enzyme activity. Potassium is important in the controlling of rates of photosynthesis and respiration.
Formula: NH3, Physical state: Gas
Preparation of ammonia
Laboratory preparation of ammonia
In the laboratory, ammonia gas can be prepared by the action of heating an alkali with an ammonium compound.
The test tube must be tilted downwards to prevent the water formed from running back into the reaction mixture which may boil and cause an explosion.
Method of collection: Ammonia gas is collected by down ward displacement of air because it is less dense than air. Drying agent used: Calcium oxide
Drying agents like calcium chloride and concentrated sulphuric acid should not be used because they easily react with ammonia.
Physical properties of ammonia
- It is a colourless gas with a pungent choking smell
- It is less dense than air
- It is very soluble in water
- It is easily liquefied, either by cooling to -33oC or by compressing. This makes it easy to transport in tanks and cylinders.
Chemical properties of ammonia
- It turns damp red litmus paper blue
- It burns in pure oxygen with a yellow - brown flame
- It dissolves in water to form ammonium hydroxide
- It is a reducing agent because it reduces oxides to metals low in the reactivity series of metals.
Test for ammonia gas
Ammonia gas turns damp red litmus paper blue. It is alkaline in nature
Industrial preparation of ammonia
The industrial preparation of ammonia is called Haber process. Ammonia gas produced industrially from nitrogen and hydrogen
Importance of Haber process
Haber process is important because it produces ammonia on a large scale
Raw materials for Haber process
Sources or raw of nitrogen and hydrogen
1. Nitrogen Source: Liquid air (obtained by fractional distillation)
Nitrogen is obtained by burning hydrogen in air. Air is mostly nitrogen and oxygen, with small amounts of other gases. Only the oxygen reacts with hydrogen, forming steam:
When the steam condenses, the gas that remains is mainly nitrogen.
2. Hydrogen Source: Methane (natural gas) Steam. Hydrogen is made from methane and steam.
Reaction between nitrogen and hydrogen
N2(g) + 3H2(g) ⇌ 2NH3(g)
Uses of ammonia
- It is used in the refrigerating plants as a refrigerant
- It is used in the manufacture of explosives
- It is used in the manufacture of plastics and glue
- It is used in the manufacture of nitric acid
- It is used as a cleaning agent
- It is used in the manufacture of fertilizers such as ammonium sulphate, ammonium nitrate and ammonium phosphate.
- Ammonium sulphate is used as a fertilizer because it contains nitrogen and sulphur needed by plants
- Ammonium nitrate is used as a fertilizer because it contains nitrogen needed by plants
- Ammonium phosphate is used as a fertilizer because it contains nitrogen and phosphorous needed by plants
- The three essential elements present in many fertilizers are nitrogen, phosphorous and potassium (N.P.K)
Problems with chemical fertilizers
- Chemical fertilizers tend to make the soil acidic if they are used for long periods of time
- Chemical fertilizers are easily leached away e.g. nitrates (NO3 - ), sulphate (SO4 2-) and chlorides (Cl- ). They are leached because they easily dissolve in water and move with it. This is wasteful. Besides, when the rainwater drains into rivers, the nitrates cause pollution