Nitric Acid


Nitrogen forms oxoacids in nature. eg  , , etc.

 is also referred as Nitric Acid 


Preparation

Nitric acid is prepared by heating KNO3 or NaNO3 and concentrated H2SO4 in a glass retort:

Bulk Quantitites of Nitrix Acid is prepared by Ostwald’s process. This method is based upon catalytic oxidation of NH3 by atmospheric oxygen.

Nitric oxide thus formed combines with oxygen giving NO2 :- . Nitrogen dioxide so formed, dissolves in water to give HNO3. :- 


Properties

  • It is a colourless liquid
  • Laboratory grade nitric acid contains ~ 68% of the HNO3 by mass and has a specific gravity of 1.504.
  • HNO3 exists as a planar molecule in gaseous state
  • Nitric acid behaves as a strong acid giving hydronium and nitrate ions in aqueous state:
  • Concentrated nitric acid is a strong oxidising agent and attacks most metals except noble metals
  • Some metals (e.g., Cr, Al) do not dissolve in concentrated nitric acid because of the formation of a passive film of oxide on the surface
  • Concentrated nitric acid also oxidises non–metals and their compounds. Iodine is oxidised to iodic acid, carbon to carbon dioxide, sulphur to H2SO4, and phosphorus to phosphoric acid.


  • Brown Ring Test: 

Nitric oxide reacts with Fe2+ to form a brown coloured complex. The test is carried out by adding dilute ferrous sulphate solution to an aqueous solution containing nitrate ion, and then carefully adding concentrated sulphuric acid along the sides of the test tube.

A brown ring at the interface between the solution and sulphuric acid layers indicates the presence of nitrate ion in solution.



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