Nitric acid is highly corrosive mineral acid and commonly referred as the spirit of niter. Nitric acid is considered as one of the most important chemical products because of its commercial applications. The different forms of nitric acid are available in the marketplace which are fuming nitric acid and anhydrous nitric acid.
General properties of Nitric Acid
- Nitric acid is a strong corrosive acid at ambient temperature and strong oxidizing agent.
- Nitric acid is commercially available in an azetrope composition with the water molecule.
- Nitric acid is colorless and tends to acquire a yellow color due to decomposition into oxides of nitrogen and water.
- Pure form of nitric acid is not stable and even at ordinary temperature it undergoes slight decomposition.
Ostwald process is a chemical process for commercial nitric acid preparation and it is developed by the Wihelm Ostwald in 1902. The Ostwald process is one of the most important process and it provides raw material for the fertilizer industry. Ammonia (NH3) is used as a raw material for the production of Nitric acid in Ostwald process and it’s obtained from the Haber’s process. Catalyst such as Platiunum combined with 10% Rhodium is used in the Ostwald process.
4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g)
2 NO (g) + O2 (g) → 2 NO2 (g)
3 NO2 (g) + H2O (l) → 2 HNO3 (aq) + NO (g)
Aqueous HNO3 obtained from the Ostwald process can be concentrated by distillation up to 68% and further concentration to 98% can be achieved by dehydration with concentrated H2SO4.
Nitric acid is made by laboratory synthesis by thermal decomposition of cupric nitrate producing nitrogen oxide and oxygen. Nitrogen oxide gases, which then passed through the water to produce nitric acid and byproduct as sodium sulphate.
2 Cu(NO3)2 → 2 CuO (s) + 4 NO2 (g) + O2 (g)
4 NO2 (g) + O2 (g) + 2 H2O (l) → 4 HNO3 (aq)
Nitric acid is also alternatively produced by the sodium nitrate salt with highly concentrated sulphuric acid. High purity, red fuming Nitric acid is obtained from distilling this mixture around 830C. The distillate red fuming nitric acid is then converted to the white fuming nitric acid.
2 NaNO3 + H2SO4 → 2 HNO3 + Na2SO4