3

METHODS OF PREPARATION

3

3

2

4





COMMERCIAL METHOD:

General principle:

2

Process:

2 and O 2 from atmosphere are allowed to combine with each other is the presence of electric are at 3000°C.







and Ofrom atmosphere are allowed to combine with each other is the presence of electric are at 3000°C.

This reaction is endothermic and is favoured at high temperature.The gases which come out from this electric fieid contain 1. 25 % of NO. These gases are rapidly cooled down to 1000 °C.



At 600°C, NO combines with oxygen to form NO 2.







NO 2 is cooled down to 50°C by water pipes. NO 2 is absorbed in water in a tower in which the water trickles down Fig (1.1) NO



HNO 2 is oxidized to HNO 3 and NO. NO is re-oxidized to NO 2 and thus to HNO 3 . HNO





Preparation of conc. HNO 3 :

There are three stages to get 100 % HNO 3 . Dil HNO 3 , 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 HNO 3.

. Dil HNO , 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 HNO If concentrated H 2 SO 4 , is used and distilled with 68 % HNO 3 ,, then we get 98% HNO 3 , H 2 SO 4 , absorbs the water.

SO , is used and distilled with 68 % HNO ,, then we get 98% HNO , H SO , absorbs the water. If we want to get 100% HNO 3 , then 98% HNO 3 , is strongly cooled. Pure acid is deposited as colorless crystals at - 42°C. These crystals are separated and melted to get 100 % HNO 3 .

Physical properties:

Pure HNO 3 , 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 HNO 3 , 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. CHEMICAL PROPERTIES OF NITRIC ACID: Decomposition: HNO 3 , decomposes in the presence of light even at ordinary temperature





Acidic property: HNO 3 is a strong acid. It ionizes in water to give sufficient protons. it's dissociation constant is in the range of 10 +3. On the basis of acidic nature, it reacts with many oxides, hydroxides, carbonates bicarbonates, sulphites and bisulphites. In this way metal nitrates are produced.

Reaction with calcium oxide (CaO): Reaction with NaOH and KOH: Reaction with Na 2 CO 3: Reaction with NaHCO 3:

, is a chemical of great commercial importance. There are three important methods for its manufacture., can be prepared on large scale by beating Chile salt petre with conc. HSOThe nitrogen and from the air can be made to combine by electric discharge. NO produced which is further oxidized to NO, and is then dissolved in water.