Nitric acid (HNO₃) is a highly corrosive and toxic mineral acid with a colorless or yellowish appearance. It is also known as aqua fortis or “strong water.” When exposed to light, it gradually turns yellow due to decomposition into nitrogen oxides. Nitric acid is primarily used in various industrial processes, including the production of fertilizers, explosives, and metal treatments.
Nitric acid (HNO₃) has several important temperature-related properties, which vary depending on its concentration. Here are some key temperature characteristics:
Freezing Point:
Pure nitric acid (100%) freezes at −42°C (−43.6°F).
Concentrated nitric acid (68–70%, the typical industrial concentration) has a slightly higher freezing point, usually around −30°C (−22°F).
Boiling Point:
Pure nitric acid boils at 83°C (181.4°F).
Concentrated nitric acid (68–70%) boils at 120.5°C (248.9°F).
Uses of Nitric Acid
- Fertilizer Production: The largest use of nitric acid is in the production of fertilizers, specifically ammonium nitrate. This compound is essential for agriculture as a nitrogen-rich fertilizer that promotes plant growth.
- Explosives Manufacturing: Nitric acid is a key component in making explosives like nitroglycerin, TNT (trinitrotoluene), and RDX (Research Department Explosive). These explosives are widely used in mining, construction, and military applications.
- Rocket Propellant: In aerospace applications, nitric acid has been used as an oxidizing agent in liquid rocket propellants. It was once a part of the fuel systems for early rocket designs.
- Gold and Silver Refining: Nitric acid is used to refine precious metals like gold and silver. When combined with hydrochloric acid (a mixture called aqua regia), it dissolves gold, allowing for its separation and purification.
Interesting Facts About Nitric Acid
- Aqua Fortis: Nitric acid was historically known as “aqua fortis,” meaning “strong water” in Latin. Alchemists used it to dissolve metals, particularly silver, which led to its nickname.
- Vital in Early Explosive Development: Nitric acid played a crucial role in the development of modern explosives. Its reaction with glycerol produces nitroglycerin, a highly explosive compound used in dynamite, which revolutionized mining and construction industries.
- Famous in Alchemy: In alchemy, nitric acid was an important reagent for dissolving metals and searching for the Philosopher’s Stone, a substance believed to transform base metals into gold.
- Aqua Regia and Gold: Nitric acid, when combined with hydrochloric acid, forms “aqua regia,” one of the few substances capable of dissolving gold. This mixture is used for gold refining and purification.
- Handling and Storage Dangers: Nitric acid is highly corrosive and can cause severe burns when it comes into contact with skin. It also emits toxic fumes that can cause respiratory issues. Accidents involving nitric acid spills or mishandling can result in serious injuries and environmental damage.
- Historical Explosions: Several historical accidents have occurred due to the mishandling of nitric acid in explosive manufacturing. One of the most notable incidents is the Oppau Explosion in 1921, Germany, where a nitrogen-fertilizer storage depot exploded, killing over 500 people. The improper handling of ammonium nitrate, a product of nitric acid, contributed to the disaster.
- Military Use of Nitric Acid: Nitric acid’s role in making explosives has drawn ethical concerns, especially regarding its use in military conflicts. Its involvement in the production of explosives like TNT and RDX has led to debates over arms control and the environmental impact of military activities.
- Rocket Accidents: Nitric acid, used as an oxidizing agent in early rocket fuels, has been involved in several rocket-related accidents. For instance, the failure of early rocket engines using nitric acid and hydrazine led to explosions during testing, highlighting its volatile nature.