Nitric Acid
Definition and meaning of Nitric Acid in chemistry.
Nitric acid is a highly corrosive mineral acid with the chemical formula HNO3. It is a colorless liquid in its pure form, but older samples tend to acquire a yellow cast due to decomposition into oxides of nitrogen and water. Nitric acid is a strong oxidizing agent and a strong acid that completely dissociates in aqueous solutions.
In more detail
Commercially, nitric acid is manufactured by the Ostwald process, which involves the catalytic oxidation of ammonia with oxygen to yield nitric oxide, followed by oxidation to nitrogen dioxide and subsequent absorption in water. The primary industrial use of nitric acid is the production of fertilizers, such as ammonium nitrate, which accounts for the vast majority of its global consumption. It is also a critical precursor for the manufacture of chemical explosives like trinitrotoluene, nitroglycerin, and RDX, as well as precursors to nylon and polyurethanes. Due to its powerful oxidizing properties, nitric acid reacts vigorously with many nonmetals and most metals, dissolving even noble metals like silver and copper, though it cannot dissolve gold on its own. A mixture of concentrated nitric acid and hydrochloric acid, known as aqua regia, generates nitrosyl chloride and elemental chlorine, giving it the unique ability to dissolve gold and platinum. The acid must be handled with extreme care, as contact with skin causes severe chemical burns and stains the tissue yellow due to reactions with keratin proteins.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Formula | HNO3 |
| Molar mass | 63.012 g/mol |
| Density | 1.51 g/cm³ |
| Boiling point | 83 °C |
When a piece of copper is placed in concentrated nitric acid, it rapidly dissolves to produce a blue-green solution of copper(II) nitrate and toxic, brown nitrogen dioxide gas.
Frequently asked questions
What is aqua regia?
Aqua regia is a fuming mixture of nitric acid and hydrochloric acid, typically in a 1:3 molar ratio, capable of dissolving noble metals like gold.
Why does concentrated nitric acid turn yellow over time?
It slowly decomposes upon exposure to light and heat, releasing nitrogen dioxide gas which remains dissolved in the acid and imparts a yellow or brown color.