5 d) Industrial manufacture of chemicals

Question 1

5.22 understand that nitrogen from air, and hydrogen from natural gas or the cracking of hydrocarbons, are used in the manufacture of ammonia

Answer 1

Ammonia (NH3) is manufactured by using nitrogen from air and hydrogen from natural gas.

N2(g) + H2(g) ==> NH3 (g)

Question 2

5.23 describe the manufacture of ammonia by the Haber process, including the essential conditions: i a temperature of about 450°C

Answer 2

i) a temperature of about 450c
ii) a pressure of about 200 atmospheres
iii) an iron catalyst:
Ammonia is manufactured by combining nitrogen and hydrogen in an important industrial process called the Haber process.

nitrogen + hydrogen ⇄ symbol ammonia

N 2 (g) + 3H 2 (g) ⇄ symbol 2NH 3 (g)

The Haber process:

Raw materials: nitrogen (from the air) & hydrogen :(made from natural gas)
The proportions: 1 volume of nitrogen to 3 volumes of hydrogen
The temperature: 450oC
The pressure: 200 atmospheres
The catalyst: iron
Each time the gases pass through the reaction vessel, only about 15% of the nitrogen and hydrogen combine to make ammonia. The reaction mixture is cooled and the ammonia condenses as a liquid. The unreacted nitrogen and hydrogen can simply be recycled through the reactor.

Question 3

5.24 understand how the cooling of the reaction mixture liquefies the ammonia produced and allows the unused hydrogen and nitrogen to be recirculated

Answer 3

The products from the reactant are sent through a cooling mechanism, this is at a temperature that condenses ammonia, but not hydrogen and nitrogen. Liquid ammonia is then collected but hydrogen and nitrogen float right back into the reactor.

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Question 4

5.25 describe the use of ammonia in the manufacture of nitric acid and fertilisers

Answer 4

Manufacture of Nitric acid:

Industrially, nitric acid is made by the catalytic oxidation of ammonia over heated platinum. Oxidising ammonia produces oxides of nitrogen which can then be dissolved in water to produce nitric acid.

Initially nitrogen(II) oxide will be formed from the catalytic oxidation of ammonia using the transition metal platinum. 4NH3 (g) + 5O3 (g) ==> 4NO(g) + 6H2O (g)

The nitrogen(II) oxide is rapidly cooled before combining with oxygen (from excess air) to form nitrogen(IV) oxide. 2NO(g) + O2(g) ⇌ 2NO2 (g)

The nitrogen(IV) oxide is now allowed to react with water to form nitric acid. 4NO2 (g) + O2 (g) + 2H2O (l) ==> 4HNO3 (aq)

Most of the nitric acid made is used to make the all-important fertilisers such as ammonium nitrate.

Manufacture of Fertilizers:

The main use of ammonia is in the manufacture of fertilizers. Approximately 75% of all ammonia produced is converted into various ammonium compounds like ammonia sulphate, ammonium nitrate and urea (NH2CONH2). These compounds are called nitrogenous fertilizers. They are solids for ease in handling and water soluble so that they seep into the soil to be absorbed by the roots of the plant.