NO3

NO3 commonly denotes the nitrate ion, NO3−, a widespread polyatomic anion in inorganic chemistry. In some contexts, NO3 may also refer to the nitrate radical NO3•, a transient species observed in atmospheric chemistry, but the nitrate ion is by far the more common meaning.

In the nitrate ion, nitrogen is in the +5 oxidation state. The three N–O bonds are equivalent due to resonance, giving a trigonal planar geometry with bond angles near 120 degrees. The three resonance structures distribute the negative charge over the oxygen atoms, resulting in an overall charge of −1 and an average N–O bond order of about 1.33. The nitrate ion is typically found as salts, such as sodium nitrate, potassium nitrate, or ammonium nitrate, which are generally soluble in water.

NO3 is the conjugate base of nitric acid (HNO3). Nitric acid is a strong acid, with a very low pH in aqueous solution, and nitrates tend to remain dissociated as NO3− in water. In chemistry and industry, nitrate salts serve as oxidizing agents and sources of nitrogen. They are used in fertilizers, where nitrate supplies essential plant nutrients, and in the production of explosives and propellants. Nitrates are also encountered in food processing as curing agents when converted to nitrites by bacterial action.

Safety and environment: nitrates are strong oxidizers and can pose health and environmental risks. In drinking water, elevated nitrate levels can cause methemoglobinemia in infants and contribute to eutrophication in aquatic systems. Regulations typically limit nitrate concentrations to protect health and ecosystems.