Nitric acid

Nitric acid is, after H₂SO₄, the second most produced mineral acid worldwide — about 60 Mt/yr. Its industrial centrality comes from two uses: ~80 % goes to ammonium nitrate NH₄NO₃ manufacture (major agricultural fertiliser, but also the ANFO primary explosive), and ~10 % to military and civilian explosives derivatives (TNT, nitroglycerin, nitrocellulose). The remainder feeds metallurgy (stainless steel pickling, aqua regia 3:1 HCl/HNO₃ which dissolves gold and platinum), microelectronics (silicon wafer etching) and organic synthesis (aromatic nitrations for dyes and medicines).

The Ostwald process, developed by Wilhelm Ostwald in 1902, is universal: catalytic oxidation of ammonia on platinum-rhodium gauzes at 850 °C (4 NH₃ + 5 O₂ → 4 NO + 6 H₂O), thermal oxidation of NO to NO₂ with excess air, then absorption of NO₂ in water to form HNO₃ + NO. The process consumes ammonia from Haber-Bosch — together the two processes form the "nitrogen pipeline" underpinning all modern agriculture.

Chemically, HNO₃ is a strong acid (pKa = -1.4) and a powerful oxidiser thanks to its +V oxidation-state nitrogen. This duality makes it dangerously reactive: it dissolves most common metals while generating nitrogen oxides, and passivates aluminium and iron by forming a protective oxide film (which is why concentrated HNO₃ is transported in aluminium tanks). Red fuming nitric acid, containing ~16 % dissolved NO₂, gives off toxic orange fumes and is used as a rocket oxidiser (Titan II, Saturn IB, certain military launchers).