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November 22, 2024Ammonia, a colourless gas with a distinct odour, is a chemical building block and a significant component in producing many everyday items. It is found naturally in the air, soil, water, and in plants and animals, including people.
Nitrogen is the first member of group \(15\) of the periodic table. Daniel Rutherford discovered nitrogen in \(1772\) Several compounds are made of nitrogen like nitric acid, nitrogen dioxide, ammonia, ammonium hydroxide, etc. The article will learn everything about ammonia, its structure, physical and chemical properties, preparation, manufacture by Haber’s process and uses.
Ammonia is an important compound of nitrogen and hydrogen. It contains one nitrogen atom and three hydrogen atoms. Its chemical formula is \({\text{N}}{{\text{H}}_3}.\) Ammonia is produced by the natural decomposition of animal and plant bodies because, with the death and decay of plants and animals, the nitrogen compounds present in them decomposed to give ammonia. Ammonia also occurs in the soil in the form of ammonium salt.
Example: Formation of ammonia by the decomposition of nitrogenous organic matter urea \(\left({{\text{N}}{{\text{H}}_2}{\text{CON}}{{\text{H}}_2}}\right).\)
\({\text{N}}{{\text{H}}_2}{\text{CON}}{{\text{H}}_2} + 2{{\text{H}}_2}{\text{O}} \to {\left( {{\text{N}}{{\text{H}}_4}} \right)_2}{\text{C}}{{\text{O}}_3} \rightleftharpoons 2{\text{N}}{{\text{H}}_3} + {\text{C}}{{\text{O}}_2} + {{\text{H}}_2}{\text{O}}\)
The ammonia molecule is formed due to the overlap of three \({\text{s}}{{\text{p}}^3}\) hybrid orbitals of nitrogen and \({\text{s}}\) orbitals of three hydrogens. The \({{\text{4}}^{{\text{th}}}}\,{\text{s}}{{\text{p}}^3}\) hybrid orbital of nitrogen is occupied by a lone pair of electrons. This gives a trigonal pyramidal geometry to the ammonia molecule.
The \({\text{H-N-H}}\) angle is \({107.8^ \circ }\) with \({\text{N-H}}\) bond length \(101.7\,{\text{pm}}.\) The \({\text{H-N-H}}\) bond angle is slightly less than the tetrahedral angle of \({109^ \circ }28’\) due to the lone pair-bond pair repulsion, which tends to push the \({\text{N-H}}\) bond slightly inwards. In liquid and solid states, ammonia is associated due to hydrogen bonding.
1. By heating ammonium salts with a strong base: On a small scale, ammonia is prepared by heating ammonium salts with a strong base.
\({\left({{\text{N}}{{\text{H}}_4}} \right)_2}{\text{S}}{{\text{O}}_4} + 2{\text{NaOH}} + {\text{Heat}} \to 2{\text{N}}{{\text{H}}_3} + 2{{\text{H}}_2}{\text{O}} + {\text{N}}{{\text{a}}_2}{\text{SO}}4\)
\({\text{N}}{{\text{H}}_4}{\text{Cl}} + {\text{KOH}} + {\text{Heat}} \to {\text{N}}{{\text{H}}_3} + {{\text{H}}_2}{\text{O}} + {\text{KCl}}\)
In the laboratory, ammonia is prepared by heating a mixture of slaked lime and ammonium chloride.
\(2{\text{N}}{{\text{H}}_4}{\text{Cl}} + {\text{Ca}}{\left({{\text{OH}}} \right)_2} + {\text{Heat}} \to 2{\text{N}}{{\text{H}}_3} + 2{{\text{H}}_2}{\text{O}} + {\text{CaC}}{{\text{l}}_2}\)
2. By the hydrolysis of metal nitrides: Ammonia gas can also be produced by hydrolysis of metal nitrides like magnesium and aluminium nitride, with water or alkalies.
\({\text{M}}{{\text{g}}_3}~{{\text{N}}_2} + 6{{\text{H}}_2}{\text{O}} \to 2{\text{N}}{{\text{H}}_3} + 3{\text{Mg}}{\left({{\text{OH}}} \right)_2}\)
\({\text{AlN}} + 3{{\text{H}}_2}{\text{O}} \to {\text{N}}{{\text{H}}_3} + {\text{Al}}{\left({{\text{OH}}} \right)_3}\)
Ammonia gas is dried by passing over quicklime \(\left({{\text{CaO}}} \right).\) Ammonia being a basic gas, cannot be dried by passing through concentrated sulphuric acid or phosphorus pentoxide, because it reacts with them to form ammonium sulphate or ammonium phosphate, respectively. Calcium chloride also cannot be used for drying ammonia gas as it forms ammoniates with calcium chloride.
On a commercial scale, ammonia is manufactured by Haber’s process.
\({{\text{N}}_2}\left({\text{g}} \right) + 3{{\text{H}}_2}\left({\text{g}} \right) \rightleftharpoons 2{\text{N}}{{\text{H}}_3}\left({\text{g}}\right);\,\Delta {{\text{H}}^ \circ } = – \,92.4\, {\text{kJ}}/{\text{mol}}\)
This reaction is reversible, exothermic and occurs with a decrease in volume. Therefore, according to Le Chatelier’s principle, the favourable conditions for the manufacture of ammonia are:
In Haber’s process, a mixture of \({{\text{N}}_2}\) and \({{\text{H}}_2}\) in the molar ratio of \(1:3\) is compressed to about \(200\) atmosphere pressure. The compressed gases are then cooled and passed through the soda lime tower to them from moisture and carbon dioxide. Then these are fed into the catalyst chamber packed with iron oxide with a small amount of \({{\text{k}}_2}{\text{O}}\) and \({\text{A}}{{\text{l}}_2}{{\text{O}}_3}.\) The chamber is heated electrically to a temperature of \(700\,{\text{K}},\) when the two gases combine to form ammonia. The reaction is exothermic, the heat involved maintains the desired temperature, and further electrical heating is not required.
There is approximately \(15 – 20\) per cent ammonia, in the gases leaking from the chamber, and the remaining are nitrogen and hydrogen without reaction. They pass through the condensing pipe, which liquefies and collects ammonia from the receptor. The gases that are not reacted are pumped back to the compression pump where the fresh gas mixture is mixed.
The various applications of Ammonia are discussed below:
Ammonia is one of the important compounds of nitrogen. In the article, Ammonia: Preparation, Structure, Properties and Uses, you have gained knowledge on what is ammonia? Its physical properties, structure, and different preparation methods with the emphasis on Haber’s process. Apart from this, chemical properties such as basic nature, Lewis base, combustion and oxidation and uses of ammonia is clear from this article.
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Q.1. What are the properties of ammonia?
Ans: Ammonia is a colourless gas with a characteristic pungent ammoniacal smell. It is lighter than air and can be easily liquefied at room temperature by passing a pressure of about \(8\) to \(10\) atmospheres. Its boiling point is \( – {33.5^ \circ }{\text{C}}\left({239.6\,{\text{K}}} \right)\) under one atmosphere pressure. It acts as Lewis base.
Q.2. What is the method of preparation of ammonia?
Ans: On a commercial scale, ammonia is manufactured by Haber’s process.
\({{\text{N}}_2}\left({\text{g}} \right) + 3{{\text{H}}_2} \rightleftharpoons {\text{N}}{{\text{H}}_3}\left({\text{g}} \right);\Delta {{\text{H}}^ \circ } = – \,92.4\,{\text{kJ}}/{\text{mol}}\)
This reaction is carried out at a temperature of \(700\,{\text{K}}\) and \(200\, \times {10^5}\,{\text{Pa}}\) or \(200\,\) atmosphere pressure in the presence of iron oxide as a catalyst with a small amount of \({{\text{K}}_2}{\text{O}}\) and \({\text{A}}{{\text{l}}_2}{{\text{O}}_3}.\) Molybdenum is used as a promoter which increases the efficiency of the catalyst.
Q.3. What are the uses of ammonia synthesis?
Ans: Synthesised ammonia is mainly used for the manufacture of fertilizers such as ammonium sulphate, ammonium nitrate, urea, diammonium phosphate, etc. Apart from this, it is also used in the manufacture of nitric acid by Ostwald’s process, manufacture of sodium carbonate by Solvay’s process and manufacture of rayon and urea.
Q.4. What are the uses of ammonia?
Ans: Ammonia is used,
1. In the manufacture of nitric acid by Ostwald’s process, sodium carbonate by Solvay’s process and in the manufacture of rayon and urea.
2. In the manufacture of fertilizers such as ammonium sulphate, ammonium nitrate, urea, diammonium phosphate, etc.
3. As a refrigerant in ice plants.
4. As a cleaning agent for furniture and glass surfaces.
5. As an important reagent and is used as a solvent in the laboratory.
Q.5. What type of reaction is the synthesis of ammonia by Haber’s process?
Ans: The synthesis of ammonia by Haber’s process is a reversible, exothermic reaction and occurs with a decrease in volume.