The two common oxyacids of nitrogen are nitric acid, HNO3, and nitrous acid, HNO2 (Figure 22.36). Nitric acid is a colorless, corrosive liquid. Nitric acid solutions often take on a slightly yellow color (Figure 22.37) as a result of small amounts of NO2 formed by photochemical decomposition:
FIGURE 22.36 Structures of nitric acid and nitrous acid.
Nitric acid is a strong acid. It is also a powerful oxidizing agent, as the following standard reduction potentials indicate:
Concentrated nitric acid will attack and oxidize most metals, except Au, Pt, Rh, and Ir.
About 7.8 × 109 kg (8.6 million tons) of nitric acid is produced annually in the United States. Its largest use is in the manufacture of NH4NO3 for fertilizers, which accounts for about 80 percent of that produced. HNO3 is also used in the production of plastics, drugs, and explosives.
The development of the Haber and Ostwald processes in Germany just before World War I permitted Germany to make munitions even though naval blockades prevented access to traditional sources of nitrates. Among the explosives made from nitric acid are nitroglycerin, trinitrotoluene (TNT), and nitrocellulose. The reaction of nitric acid with glycerin to form nitroglycerin is shown in Equation 22.77: