Nitric oxide also known as nitrogen monoxide is a chemical compound made of one nitrogen and one oxygen atom. It has the chemical formula ·NO, where the · is an unpaired electron. Because of this electron, ·NO is a free radical. Nitric oxide is an important compound in both the chemical industry and in mammal biology.
Nitric oxide is a colorless gas with a sharp, sweet odor.
Nitric oxide is a rare example of a stable free radical. Most simple radicals with a single electron form a dimer, similar to the halogens. Nitric oxide usually stays as a monomer in the gas phase, only combining to dinitrogen dioxide when it is a liquid.
It is easily oxidized to nitrogen dioxide by air.[source?] It can react with a mixture of air and water to make nitrous acid.[source?] It glows when reacted with ozone.[source?]
In the chemical industry, nitric oxide is made from ammonia and oxygen in the first step of the Ostwald process. This process uses an alloy of platinum and rhodium as a catalyst. The chemical equation for this reaction is:
Nitric oxide is one of the nitrogen oxides that are made from nitrogen and oxygen in the atmosphere by a lightning strike.
It can be made in small amounts by reacting copper with nitric acid.[further explanation needed] It can also be made by reducing nitrous acid with compounds such as iron(II) sulfate.[further explanation needed]
The main use of nitric oxide in the chemical industry is making nitric acid in the Ostwald process. As of 2016, people made around 60 million tonnes of nitric acid a year, mostly by using the Ostwald process.
Nitric oxide is an important molecule in the biology of mammals. It is used by the circulatory system to control vasodilation, the growing and shrinking of blood vessels.
Nitric oxide is toxic when breathed in. It also easily is oxidized to nitrogen dioxide, a toxic brown choking substance.