Concept of Nitric acid

Nitric acid is a mineral acid used in many industrial processes. It is strongly corrosive in nature. Nitric acid is among the chief sources of organic nitrogenous compounds. However, it has some hazardous applications, such as Nuclear fuel processing. The Nitric acid formula is HNO3. 

Physical and Chemical properties of Nitric acid

Physical Properties:

• Nitric acid is a colourless chemical compound. 
• It has a freezing point of -42 degrees celsius. 
• The boiling point of nitric acid is 83 degrees celsius. 
• Nitric acid exists in liquid form at room temperature.

Chemical Properties: 

• Nitric acid decomposes in the presence of direct sunlight or heat. HNO3 dissociates into H2O, NO2, and O2. Therefore, it should be stored in dark-coloured bottles.

Note: The Nitrogen dioxide (N2O) formed as a result of thermal decomposition of HNO3 remains in the solution and hence, contaminates the pure nitric acid. It gives a reddish-yellow appearance to the HNO3. 

• Nitric acid is a strong mineral acid and gets completely ionised into its composing ions, Hydronium ion, and Nitrate ion. 
• Nitric acid acts as a strong oxidising agent and is a potent electron acceptor in several redox reactions. 

Chemical Structure of Nitric Acid

The chemical formula of Nitric acid is HNO3. It has two single bonds between nitrogen and oxygen and one double bond between nitrogen and oxygen. There are two resonating structures of nitric acid formula HNO3. One of the oxygens is bound to the hydrogen, which is released in an aqueous solution to form nitrate ions during a redox reaction. 

Chemical Reactions of Nitric acid

Nitric acid formula HNO3 is an excellent oxidising agent, and a strong mineral acid takes part in various chemical reactions. Some important ones are:

• Acid-base reactions
• Reactions with metals
• Xanthoproteic test
• Reactions with Non-metals

Acid-base Reactions: Nitric acid is among the strongest mineral acids in chemistry and readily dissociates into hydronium ion (H3O+) and Nitrate ion (NO3-) in an aqueous solution. However, nitric acid can also act as a base in reactions with a stronger mineral acid such as Sulphuric acid formula H2SO4. 

Additionally, having dual properties of an acid and a base, nitric acid also shows a reaction of autoprotolysis. It reversibly dissociates into the water, nitrate ions, and nitrite ions. 

Reactions with Metals: As nitric acid having the chemical formula of HNO3 acts as a strong mineral acid, it liberates hydrogen gas (H2) upon reaction with certain metals such as magnesium, zinc, etc. It also oxidises some metals such as Copper and Silver.

Note: The oxidising property of nitric acid converts the silver surface into a blackish greenish colour. 

Xanthoproteic Test: It is a type of biochemical analytic test used to detect the presence of proteins in clinical specimens such as Bloor or urine. The reaction of nitric acid HNO3 with proteins leads to the formation of yellow coloured derivatives of nitrate. Further confirmation is made by adding ammonia to the solution, upon which the yellow colour turns into orange colour.

Note: Improper handling of nitric acid during lab work leads to yellowish-orange spots on hands and arms due to spillage of nitric acid and its reaction with organic proteins present in the skin tissues. 

Reactions with Non-metals:  Being a strong oxidising agent, nitric acid oxidises Non-metals such as carbon, iodine, and other halogens. 

Synthesis of Nitric acid (HNO3)

The production of nitric acid is of great significance from an industrial aspect. The commercial production of nitric acid is done using the Ostwald process, in which platinum gauze catalyst is used. It catalyses the conversion of anhydrous ammonia to nitric oxide. The nitric oxide formed is then converted to nitrogen dioxide by reacting with air. In the final step, the nitrogen dioxide is converted to nitric acid by absorbing into water. 

Commercially concentrated HNO3 is obtained by distillation of crude nitric acid using purification techniques. 

Uses of Nitric acid

Nitric acid is a strong mineral acid and a potent oxidising agent. These chemical properties of HNO3 form the basis of its various uses in industrial applications. Some of the important uses are: 

• Acts as a precursor for organic nitrogenous compounds. 
• Chiefly used as an oxidant in the chemical industry. 
• Used as an oxidant in liquid propellant-based rockets. 
• Aqua regia, a mixture of nitric acid with hydrochloric acid, is used to melt noble metals such as gold and platinum. 
• Used as a biochemical analytical reagent for detection of proteins using Xanthoproteic test. 
• The woodworking industry utilises low concentrations of nitric acid. 
• Used as a point-of-care test for abuse of alkaloids. 
• Used in applications based on nuclear fuel reprocessing. 

Conclusion

Nitric acid is a mineral acid used in many industrial processes. It is strongly corrosive in nature. Nitric acid is among the chief sources of organic nitrogenous compounds. There are two resonating structures of nitric acid formula HNO3. One of the oxygens is bound to the hydrogen, which is released in an aqueous solution to form nitrate ions during a redox reaction. The commercial production of nitric acid is done using the Ostwald process, in which platinum gauze catalyst is used.