Nitric Acid: A Key Mineral Acid in Modern Industry

Nitric acid is one of the most important and widely used strong mineral acids in chemistry. With its powerful oxidizing and nitrating properties, nitric acid plays a critical role in the production of fertilizers, explosives, dyes, and pharmaceuticals, and is a cornerstone in both laboratory and industrial chemistry.

What is Nitric Acid?

Nitric acid (HNO₃) is a highly corrosive and toxic strong acid composed of hydrogen, nitrogen, and oxygen. It is a colorless to pale yellow liquid that releases pungent, acrid fumes, especially in concentrated form. Over time, especially when exposed to light or heat, it can turn yellow or red due to the formation of nitrogen dioxide (NO₂).

Chemical Formula: HNO₃

Molecular Weight: 63.01 g/mol

CAS Number: 7697-37-2

Common Names: Aqua fortis, spirit of niter

Key Physical and Chemical Properties

Property	Value
Appearance	Colorless to yellow fuming liquid
Odor	Pungent, suffocating
Density (conc. ~68%)	~1.41 g/cm³
Boiling Point	83 °C (decomposes)
Melting Point	–42 °C
pKa	–1.4 (strong acid)
Solubility	Completely miscible with water
Oxidizing Ability	Very strong (especially when hot)

Nitric acid is both a strong acid (fully dissociates in water) and a strong oxidizer, capable of reacting violently with many organic and inorganic substances.

Grades of Nitric Acid

Fuming Nitric Acid (Red or White):
- 86% HNO₃
- Emits dense vapors; extremely corrosive
- Used in rocket propellants and high-performance nitrations
Concentrated Nitric Acid:
- Typically 68–70% HNO₃
- Commonly used in laboratories and industry
Dilute Nitric Acid:
- <20% HNO₃
- Used in cleaning, metal surface treatments, and certain analytical procedures

Major Industrial and Laboratory Applications

1. Fertilizer Production

Used to produce ammonium nitrate (NH₄NO₃), a widely used nitrogen-based fertilizer

2. Explosives and Propellants

Key reagent in the manufacture of TNT, nitroglycerin, and nitrocellulose
Utilized in rocket fuels and aerospace applications

3. Metallurgy and Metal Processing

Involved in etching, pickling, and cleaning of metals
Produces aqua regia (a mixture of nitric and hydrochloric acids) for dissolving noble metals like gold and platinum

4. Pharmaceutical and Dye Manufacturing

Nitrating agent in the synthesis of intermediates, dyes, and antibiotics

5. Laboratory Use

Common reagent in qualitative and quantitative analysis
Involved in digestion of samples for trace metal analysis

Safety and Handling

Nitric acid is classified as highly corrosive, toxic, and oxidizing. It requires stringent safety precautions during storage and use.

Health Hazards:

Skin/Eye Contact: Causes severe burns, blisters, and eye damage
Inhalation: Vapors irritate lungs; high exposure can cause pulmonary edema
Ingestion: Highly dangerous and potentially fatal

Safety Guidelines:

Always use chemical-resistant gloves, goggles, face shield, and lab coat
Work in a well-ventilated area or fume hood
Store in tightly sealed containers away from combustibles, reducing agents, and bases
In case of spill, neutralize carefully with sodium bicarbonate or dilute base, and clean up with appropriate absorbent

Environmental Considerations

Releases NOx gases, which are major air pollutants and contributors to acid rain
Must be disposed of via licensed hazardous waste handlers
Spills and leaks can damage aquatic life and alter water pH drastically

Conclusion

Nitric acid is an essential industrial chemical, valued for its reactivity, acidity, and versatility. From fertilizers to pharmaceuticals, its role in modern chemistry is both broad and indispensable. However, its corrosive and oxidative nature demands respect, responsible handling, and adherence to proper safety protocols.

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