HNO3, is a chemical of great commercial importance. There are three important methods for its manufacture.
METHODS OF PREPARATION
From potassium nitrate (KNO3):
HNO3, can be prepared on large scale by beating Chile salt petre with conc. H2SO4
The nitrogen and from the air can be made to combine by electric discharge. NO produced which is further oxidized to NO2, and is then dissolved in water.
At 600°C, NO combines with oxygen to form NO2.
NO2 is cooled down to 50°C by water pipes. NO2 is absorbed in water in a tower in which the water trickles down Fig (1.1)
Preparation of conc. HNO3:
- There are three stages to get 100 % HNO3. Dil HNO3, obtained by different methods can be concentrated to 68 % by the process of distillation. This percentage gives a constant boiling mixture. It is called commercial HNO3.
- If concentrated H2SO4, is used and distilled with 68 % HNO3,, then we get 98% HNO3, H2SO4, absorbs the water.
- If we want to get 100% HNO3, then 98% HNO3, is strongly cooled. Pure acid is deposited as colorless crystals at – 42°C. These crystals are separated and melted to get 100 % HNO3.
- Pure HNO3, is a colourless liquid
- It has a characteristic choking smell
- its B is 86°C
- Its M.P. is – 42°C,
- The specific gravity of pure HNO3, at 15°C is 1.538.
- In the crystalline state, it is transparent
- It is soluble in water in all proportions.
- In moist air, it gives fumes.
- It is hygroscopic in nature.