Nitric acid

Nitric acid is an inorganic compound with the formula HNO₃. It is a highly corrosive mineral acid, meaning it can damage living tissue and other materials on contact. Pure nitric acid is colorless, but it often appears yellow because it breaks down over time into oxides of nitrogen.

Most nitric acid used in industry is about 68% concentrated in water. When the concentration rises above 86%, it is called fuming nitric acid. Depending on how much nitrogen dioxide it contains, fuming nitric acid can be red fuming nitric acid or white fuming nitric acid.

Nitric acid plays an important role in chemistry as the main reagent for nitration. This means it adds a nitro group to organic molecules. Some of these nitro compounds are used to make stable dyes and medicines, like metronidazole, while others are sensitive and used in explosives.

It is also a powerful strong oxidizing agent, helping other materials to undergo chemical reactions more easily. Because of these useful properties, nitric acid is important in many areas, from making everyday products to supporting scientific research.

History

Nitric acid was first described in old books from the 13th century. Some believe it was known even earlier in Arabic works. Over time, scientists learned better ways to make it.

In the 1600s, a scientist named Johann Rudolf Glauber found a way to make nitric acid by mixing two other substances. Later, Antoine Lavoisier and Henry Cavendish studied how it forms naturally. Today, most nitric acid comes from a process using ammonia, which was developed after scientists learned how to make ammonia easily.

Physical and chemical properties

Nitric acid is a strong acid often found in labs and factories. When mixed with water, it forms a special mix called an azeotrope, which boils at a specific temperature. Pure nitric acid is colorless, but it often turns yellow because it breaks down and creates gases.

There are different types of nitric acid. Some have extra gases mixed in, which can change their color and properties. These types are used in making explosives and other important chemicals. The acid can also be very pure, almost without any water, and it stays clear but can turn yellow if it breaks down. It needs special care to keep it safe because it can react with light and heat.

Reactions

Nitric acid is a strong acid, meaning it easily gives away a particle called a hydrogen ion. It can also act like a base when faced with a stronger acid, such as sulfuric acid.

When nitric acid meets certain metals like magnesium, manganese, and zinc, it produces hydrogen gas. With metals like copper and silver, it creates different compounds depending on the acid's strength and temperature. Some metals, such as chromium and aluminum, form a protective layer that stops the acid from damaging them further.

Nitric acid can also react with non-metals and organic materials, sometimes creating explosive substances. It changes proteins to a yellow color, a test used to detect proteins.

Production

Nitric acid is made using a process called the Ostwald process. This process uses ammonia and oxygen from the air to create nitric acid. First, ammonia burns to form a gas called nitric oxide. This gas is then mixed with oxygen from the air to form nitrogen dioxide. Finally, nitrogen dioxide is mixed with water to make nitric acid.

In labs, scientists can also make nitric acid by mixing nitrate salts with sulfuric acid and then distilling the mixture. This process is similar to the industrial method but done on a smaller scale.

Uses

Nitric acid is mostly used to make fertilizers. It is mixed with ammonia to create ammonium nitrate, which helps plants grow. This use takes up most of the nitric acid made each year.

Nitric acid is also important for making explosives and other chemicals. It can add a special group to different compounds, which helps create new materials. For example, it is used to make TNT, a type of explosive. It is also used to help produce nylon and other important substances.

Safety

Nitric acid is a corrosive acid and a powerful oxidizing agent. It can cause serious chemical burns because it breaks down proteins and fats in living tissue, such as skin. When it touches human skin, it can leave a yellow stain that turns orange after washing.

If nitric acid gets on the skin, the best thing to do is to rinse it off with lots of water for at least 10–15 minutes. Remove any contaminated clothing and keep washing the skin. Nitric acid can also react dangerously with many other substances.