Intermediate Topic 649 of 1102 Inorganic Chemistry
Nitric Acid
A strong acid and oxidizer made by the Ostwald process.
In-depth explanation of Nitric Acid
Nitric acid, HNO3, is a strong acid and a powerful oxidizing agent. It is made by the Ostwald process, in which ammonia is oxidized over a platinum-rhodium catalyst at about 850 degrees C to nitric oxide, which is further oxidized and absorbed in water. Concentrated acid dissolves most metals except gold and platinum, and it passivates iron and aluminium. Concentrated acid mainly gives nitrogen dioxide, while dilute acid gives nitric oxide. It is used in fertilizers, explosives and dyes, and aqua regia, a mixture with hydrochloric acid, dissolves gold.
Going deeper: Nitric Acid
Key ideas: Ostwald process: 4NH3 + 5O2 gives 4NO + 6H2O over Pt-Rh gauze at about 800 C; 2NO + O2 gives 2NO2; 3NO2 + H2O gives 2HNO3 + NO. Concentrated acid is 68 percent and fumes. Reaction with metals: with Cu, concentrated gives NO2, dilute gives NO; very dilute with Zn or Mg gives N2O or NH4+. Aqua regia is 3 HCl to 1 HNO3 by volume and dissolves Au and Pt.
Common mistakes and connections: Students think HNO3 releases H2 with metals; it gives nitrogen oxides because nitrate is the oxidant, except with very dilute acid and Mg or Mn. Fe, Al, Cr are passivated by concentrated HNO3. Brown color of old acid is dissolved NO2. Links to ammonia, oxides of nitrogen, redox and nitration in organic chemistry.
Visualization of Nitric Acid
Ostwald step: ammonia oxidation over Pt-Rh at about 850 C (1120 K); at high temperature many collisions exceed the activation energy. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Copper reacts with concentrated nitric acid: Cu + 4HNO3 giving Cu(NO3)2 + 2NO2 + 2H2O.
Frequently asked questions about Nitric Acid
What is Nitric Acid?
A strong acid and oxidizer made by the Ostwald process.
Is Nitric Acid a beginner, intermediate or advanced topic?
Nitric Acid is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Nitric Acid?
Study these earlier topics in Inorganic Chemistry first: Nitrogen Family, Ammonia, Oxides of Nitrogen.
What comes after Nitric Acid?
The next topics in Inorganic Chemistry are Phosphorus Allotropes and Phosphoric Acid.
Can I practise Nitric Acid with quizzes?
Yes. The interactive lesson includes a self-check question on Nitric Acid, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Nitric Acid fits in Inorganic Chemistry
Nitric Acid is topic 34 of 113 in Inorganic Chemistry.