Ammonia and its Uses

Ammonia and its Uses

 

Nitrogen:

Nitrogen is a gas. It is the main constituent of air (78%). It plays an important role in the formation of animal and plant protein. It is also used in the manufacture of ammonia gas, an important industrial gas, through the Haber Process. We will learn how in this chapter.

 

Haber Process:

Ammonia is the most important compound of nitrogen. It is produced industrially by the Haber Process.

The raw materials for the process are hydrogen and nitrogen. Hydrogen is produced industrially by cracking oil, and nitrogen from liquefaction of air. These two gases, when obtained, are combined directly in a ratio of 3:1, and are passed over an iron catalyst at a temperature of 450°C and a pressure of 200 atm.

 

The reaction between hydrogen and nitrogen to form ammonia is a reversible process. This means that some of the ammonia formed may revert back to nitrogen and hydrogen. So to achieve the maximum yield of ammonia at the minimum cost, the reaction conditions are very carefully controlled.

  • The yield of ammonia is increased under high pressures. High pressure also increases the rate of reaction. However, maintaining high pressure is costly because expensive equipment is required.
  • A lower temperature increases the yield of ammonia and reduces the decomposition of hydrogen to nitrogen. However, a lower temperature also results in a slow reaction. At industry level, we cannot afford slow reactions. Therefore the high temperature of 450°C is a compromise for a faster reaction.
  • Even the high temperature and high pressure used to react the nitrogen and hydrogen result in a slow reaction, so an iron catalyst is used to speed up the reaction.

 

Displacement of Ammonia from its Salts:

Another way of obtaining ammonia gas is through the displacement of ammonia from its salt. For example,

 

NH4Cl (s) + NaOH (aq)      NH3 (g) + H2O (l) + NaCl (aq)

 

In this reaction, you can see that ammonia gas is produced on heating. Whenever an ammonium salt is heated with an alkali, ammonia is displaced from the salt. Lets take the example of another reaction.

 

2NH4Cl (s) + Ca(OH)2 (aq)      2NH3 (g) + 2H2O (l) + CaCl2 (aq)

 

Testing for Ammonia Gas:

Ammonia is the only common alkaline gas, so it can be identified by moist red litmus paper turning blue. However, we will learn a more specific chemical test for it now. In this test, we hold a glass rod dipped into some concentrated hydrochloric acid close to the suspected ammonia. This will give off fumes of hydrogen chloride gas which, in the presence of ammonia, form a dense, white ‘smoke’ of ammonium chloride.

In the same way, mixing a gas jar of hydrogen chloride and ammonia gas produces the same dense, white smoke, which is actually ammonium chloride.