Ammonia and Fertilisers

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Ammonia - Haber Process
How ammonia can be formed by sparking a mixture of nitrogen and hydrogen?
Describe the Haber Process is diagrammatically.
Conditions such as temperature and pressure and the reversibility of the reaction are discussed.
• Air is liquefied under pressure.
• Nitrogen is separated out by fractional distillation.
• Hydrogen is extracted from methane at high temperature.
• Nitrogen and hydrogen are combined to make ammonia.

Questions

1. Write down the word and symbol equations to obtain the hydrogen.
   
2. How is the nitrogen obtained? 3. Write down the word and symbol equations to obtain the ammonia.
   
3. Is the process exothermic or endothermic?
   
4. What are the optimal conditions to obtain the ammonia?

Answers

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  1. Methane + steam → hydrogen + carbon monoxide
     CH₄ + H₂O → 3H₂ + CO
     
  2. Fractional distillation of air.
     
  3. Nitrogen + hydrogen ⇄ ammonia
     N₂ + 3H₂ ⇄ 2NH₃
     
  4. Exothermic
     
  5. High temperature, high pressure and catalyst.

Fertilisers
Fertilisers increase crop production by replacing essential elements used by a previous crop or by increasing the levels of such elements. For example, nitrogen and phosphate are needed to build plant proteins and increase growth.
Eutrophication is a major problem with the use of fertilisers. This occurs when fertilisers are washed off the land by rainwater into rivers and lakes. The increase of nitrate or phosphate in the water encourages the growth of algae. The algae covers the water surface and prevents sunlight from reaching other water plants, which then die. Bacteria break down the dead plants and as they respire these bacteria use up the oxygen in the water causing most other living organisms to die.
Some examples of fertilisers are ammonium nitrate, ammonium phosphate,ammonium sulfate, and potassium nitrate.

Preparation of a fertiliser
Synthetic fertilisers are prepared in the lab by the reaction of an acid with an alkali. A quantity of alkali is placed in a beaker and a solution of acid is run in until the solution is neutral. This can be measured with a pH meter or by removing samples for testing with universal indicator.
The neutral solution of salt is evaporated until crystals form. These are filtered out, washed and dried in a warm oven.

How to prepare Ammonium Nitrate?

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