What is nitric acid used for?|| Nitric Acid Preparation

• Potassium Nitrate – KNO₃
• Sodium Nitrate – NaNO₂
• Ammonia Nitrate – NH₄NO₃
• Calcium Nitrate – Ca(NO₃)₂
• Nitroglycerin – C₃H₅N₃O₉
• Trinitrotoluene – C₇H₅N₃O₆
• Picric Acid – C₆H₃N₃O₇

Nitric acid has been known since ancient times. It was first made by Johann Rudolf Glauber in 1648 by heating a mixture of Shore (KNO₃) and sulfuric acid. Therefore, it is also called Shore acid.

In nature, nitric acid is found in the form of nitrate salts (KNO₃, NaNO₃).

Nitric Acid Preparation

In the laboratory, nitric acid is produced by the action of potassium nitrate or sodium nitrate with sulfuric acid.

KNO₃ + H₂SO₄ → KHSO₄ + HNO₃

NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃

In this method, after heating an equal amount of potassium nitrate or sodium nitrate and sulfuric acid in a retort, a vapor of nitric acid is produced, which is cooled to a liquid flask and obtained in a liquid state. In this method, the retort is not overheated. Most of the nitric acid is decomposed into nitrogen dioxide (NO₂) upon overheating the retort.

Concentration and refining of the nitric acid solution: Its solution mainly contains impurities of nitrogen oxides. To remove them, the mixture is distilled in vacuum by mixing approximately equal amounts of concentrated sulfuric acid with impure nitric acid. The middle part of the distilled fluid is pure and concentrated nitric acid.

Manufacture of Nitric Acid

There are two methods of industrial manufacture of nitric acid.

Birkland and eyde Process(Arc Method):-

In this method, the air has flowed into an electric furnace with the help of a blower. The temperature of the electric furnace is around 3500⁰C. Nitric oxide is formed by combining nitrogen and oxygen of air at this temperature.

N2 + O2 → 2NO

The nitric oxide gas thus produced and the remaining air is cooled to about 500⁰C in a capacitor and drains through an apparatus. Filled water, nitric oxide and air in this device reduce the temperature to about 50⁰C. And starts boiling on its own. For this reason, this device is called boiler. The gases from the boiler flow into an oxidizing column.

2NO + O₂ → 2NO₂

The NO₂ gas thus obtained is sent to a quartz-filled absorption column. In this column NO₂ gas enters from the bottom and the water keeps falling from the top. NO₂ gas is absorbed by water to form nitric acid. An aqueous solution of nitric acid is obtained at the bottom of this column.

2N₂O + H₂O → HNO₃ + HNO₂

3HNO₂ → HNO₃ + 2NO + H₂O

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Ostwald’s Method:

This method is a modern method of industrial manufacture. In this method, a mixture of ammonia (1 volume) and air (10 volumes) is passed through a catalytic chamber. The temperature of the catalytic chamber is about 800⁰C and it consists of the platinum lattice (Netting). Platinum acts as a catalyst. At this temperature, in the presence of platinum, ammonia has the following reaction with air oxygen.

4NH₃ + 5O₂ → 4NO + 6H₂O

Thus the mixture of nitric oxide and the remaining air obtained is sent to an oxidizing column. Nitric oxide gets nitrogen deoxidized in the oxidizing column.

2NO + O₂ → 2NO₂

Thus the NO₂ gas obtained flows into an absorption column like Berkland and Eyde method to form nitric acid.

2NO₂ + H₂O → HNO₃ + HNO₂

3HNO₂ → HNO₃ + 2NO + H₂O

Physical Properties

Pure nitric acid is a colorless liquid and its relative density is 1.51. In the presence of light, it decomposes slowly in nitrogen oxides. Because of this, fumes keep coming out in it. And its smell is intense. It is soluble in water in all proportions. The concentrations of dilute nitric acid used in the laboratory are 16N and 5N respectively.

Nitric Acid Uses

The main use of nitric acid is used to make various chemical substances. Among these (fertilizers: ammonia nitrate, basic calcium nitrate, etc.) and explosives (explosives: nitroglycerin, trinitrotoluene, picric acid, etc.) are prominent.

It is used in the laboratory as a major reagent. A mixture of 1 volume of concentrated NHO₃ and 3 volume of concentrated HCl is called aqua regia. This mixture also dissolves extremely insoluble substances like platinum gold.

2Au + 3HNO₃ + 9HCl → 3NOCl + 2AuCl₃ + 6H₂O

It is used in metallurgy and purification of silver and gold.

It is used in making nitrates of various metals, which are used in photography, dyeing, printing etc.

It is also used in the manufacture of medicines, perfumes, artificial silk, etc.