Discovery of Ammonia
Joseph Priestley first prepared ammonia in 1775 by heating Sal ammoniac (ammonium chloride) with slaked lime. Due to its basic nature, he called it alkaline air. In 1785, Comte Claude-Louis Berthollet determined the chemical composition of ammonia.
Occurrence of Ammonia
In Free State
* Ammonia is present in atmospheric air and in natural water in trace amounts. However in sewage water, it is present in greater proportion.
* It is also produced by decay of plant and animal tissues.
* Ammonia is released into the atmosphere by the decomposition of organic wastes of humans.
Sources of Ammonia
The destructive distillation of nitrogenous organic matters such as horns, hoofs, bones etc. of animals.
Preparation of Ammonia
By Heating any Ammonium Salt with an Alkali
Industrial Preparation of Ammonia
From Ammonical Liquor
During the destructive distillation of coal, ammonical liquor is obtained as a by-product. Ammonical liquor on further processing yields large quantities of ammonia and ammonium salts.
Ammonical liquor is boiled with milk of lime to obtain ammonia. This is passed into ice-cold water, to form liquor ammonia.
Physical Properties of Ammonia
Liquefaction : When cooled under pressure ammonia condenses to a colorless liquid, which boils at -33.4oC. When further cooled, it freezes to a white crystalline snow-like solid, which melts at -77.7oC.
Chemical Properties of Ammonia
Ammonia is neither combustible in air nor does it support combustion. However it burns in oxygen with a greenish-yellowish flame producing water and nitrogen.
Chemical Properties of Ammonia - Continued
With Heated Metallic Oxide
When passed over heated metallic oxides, ammonia reduces them to their metals.
Tests for Ammonia
A glass rod, dipped in concentrated hydrochloric acid when introduced into ammonia gas, produces thick white fumes of ammonium chloride.
Uses of Ammonia
Fertilisers, such as ammonium sulphate, ammonium nitrate, ammonium phosphate, urea etc. are manufactured with the help of ammonia.
Salts of Ammonia
Ammonia is one of the important compounds of nitrogen. Hence, the salts of ammonia are also of significant importance.
Discovery of Nitric Acid
Johann Glauber (1604-1668) prepared nitric acid by heating nitre with concentrated sulphuric acid and then condensing the vapour. While Henry Cavendish determined the composition of nitric acid, Lavoisier proved that oxygen is present in nitric acid.
Occurrence of Nitric Acid
Nitric acid is present in small quantities in the atmosphere. But during thundershowers, a large quantity of this acid is produced in the atmosphere. It then comes down as a very dilute solution in rainwater. This nitric acid present in the acid rain reacts with the minerals present in the soil and gets converted into nitrates.
Preparation of Nitric Acid
Nitric acid can be prepared by distilling a mixture of a nitrate salt with concentrated sulphuric acid. As nitric acid is a volatile acid it can be expelled by a stronger but less volatile acid such as concentrated sulphuric acid. But concentrated hydrochloric cannot be used for this process, as this acid is more volatile and so escapes out without reacting with the nitrate salt.
Nitric acid from Air
Nitric acid can also be prepared entirely from the air. Air free from moisture and carbon dioxide is subjected to an electric arc whose temperature is around 3000oC. At this temperature, nitrogen and oxygen of the air combine to form nitric oxide.
Manufacture of Nitric Acid by Ostwald's process
Nitric acid is prepared in large scale from ammonia and air.
Physical Properties of Nitric Acid
Pure nitric acid is a colourless liquid. But commercial nitric acid may be yellowish brown, due to the presence of dissolved nitrogen dioxide.
Chemical Properties of Nitric Acid
Pure nitric acid is not very stable. Even at ordinary temperature, in presence of sunlight it undergoes slight decomposition. As the temperature increases, the rate of decomposition also increases. On strong heating it decomposes completely to give nitrogen dioxide, water and oxygen.
Chemical Properties of Nitric Acid - Continued
Nitric acid is a strong oxidizing agent. When it undergoes thermal decomposition, it yields nascent oxygen as follows:
Uses of Nitric Acid
Nitric acid plays a significant role in the manufacture of various products such as:
* Explosives like trinitrotoluene (T.N.T.) nitro glycerine, gun cotton, ammonal etc.
* Fertilizers such as calcium nitrate, ammonium nitrate etc.
Nitrates
By Treating Metals with Nitric Acid
The reaction of nitric acid with sodium, potassium and calcium is too explosive. Hence, these metals cannot be used to prepare their nitrates.
Some Common Nitrates
The common name of potassium nitrate is Bengal salt petre or nitre. It can be prepared by treating the oxide, hydroxide, carbonate or hydrogen carbonate salts of potassium with nitric acid.
Summary of Action of Heat on Nitrates
The common name of potassium nitrate is Bengal salt petre or nitre. It can be prepared by treating the oxide, hydroxide, carbonate or hydrogen carbonate salts of potassium with nitric acid.
Tests for Nitric Acid and the Nitrates
Action of heat : When nitric acid or nitrates of metals other than sodium and potassium are heated, reddish brown fumes of nitrogen dioxide are produced.
Summary
Ammonia is produced by decay of plant and animal tissues. Nitrogenous organic matters like urea in the urine and excreta of animals get acted upon by bacteria releasing ammonia.
