Nitric Acid (HNO₃) — Properties, Uses & Safety

Overview

Nitric acid (HNO3) is a strong, highly corrosive mineral acid with a molar mass of 63.01 g/mol. At standard conditions, it is a colorless to yellowish liquid that fumes in moist air, with the yellow color in concentrated solutions resulting from dissolved nitrogen dioxide (NO2) produced by photochemical decomposition. Nitric acid is one of the most important industrial chemicals, with global production exceeding 60 million metric tons annually. The Ostwald process — the industrial method for producing nitric acid — involves catalytic oxidation of ammonia over platinum-rhodium gauze (4 NH3 + 5 O2 -> 4 NO + 6 H2O), followed by further oxidation and absorption in water. This process connects directly to the Haber process for ammonia synthesis, forming a critical link in the nitrogen chemistry chain. GHS hazard codes include H272 (may intensify fire as an oxidizer), H290 (corrosive to metals), H314 (causes severe skin burns and eye damage), and H331 (toxic if inhaled). Concentrated nitric acid can cause severe chemical burns and produces toxic nitrogen oxide fumes. Nitric acid's primary use is in manufacturing ammonium nitrate fertilizer, which supports global food production. It is also essential for producing explosives (TNT, nitroglycerin, and RDX through nitration reactions), dyes, pharmaceuticals, and rocket propellants. In the laboratory, nitric acid dissolves most metals (except gold and platinum) and is a component of aqua regia (a mixture with hydrochloric acid that can dissolve gold). For chemistry students, nitric acid connects to numerous curriculum topics: strong acid behavior and complete dissociation in water, oxidation-reduction reactions (HNO3 is both an acid and an oxidizing agent), the Ostwald process as an example of industrial catalysis, and nitration as a key reaction in organic chemistry. The acid's ability to passivate certain metals like aluminum and chromium by forming protective oxide layers introduces the concept of corrosion resistance.

IUPAC Name

nitric acid

CAS Number

7697-37-2

PubChem CID

944

Molecular Formula

HNO₃

Molar Mass

63.013 g/mol

State at STP

liquid

Appearance

Colorless to yellow liquid; fuming