A strong acid and a powerful oxidising agent. It dissolves metals that hydrochloric acid cannot, and turns copper into brown fumes.
Nitric acid is made by gently heating sodium nitrate with concentrated sulphuric acid: NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃. The vapour is condensed in a cooled receiver, using all-glass apparatus. The acid turns yellow on standing because a little decomposes: 4HNO₃ → 4NO₂ + 2H₂O + O₂.
Why is an all-glass apparatus used to prepare nitric acid?
Nitric acid vapour attacks cork and rubber, so only glass joints can be used
Why does concentrated nitric acid turn yellow on standing?
It decomposes slightly in light to give brown nitrogen dioxide, which dissolves in the acid
What mass of nitric acid is obtained from 85 g of sodium nitrate? (Na = 23, N = 14, O = 16, H = 1)
NaNO₃ has molar mass 85 and HNO₃ has 63, and one mole gives one mole, so 63 g
In industry, ammonia and air pass over hot platinum gauze at about 800 °C: 4NH₃ + 5O₂ → 4NO + 6H₂O. The nitric oxide is cooled and oxidised: 2NO + O₂ → 2NO₂. The nitrogen dioxide is absorbed in water with more air: 4NO₂ + O₂ + 2H₂O → 4HNO₃.
What is the catalyst in the Ostwald process, and what is the first product?
Hot platinum gauze; the first product is nitric oxide (NO)
Which brown gas forms in the second step?
Nitrogen dioxide, NO₂
Nitric acid is a strong acid and a powerful oxidising agent. It does not usually give hydrogen with metals, because it oxidises the hydrogen to water. With copper: Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O (concentrated) and 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O (dilute). With hot concentrated acid, carbon is oxidised: C + 4HNO₃ → CO₂ + 4NO₂ + 2H₂O.
What gas forms when copper reacts with concentrated nitric acid, and with dilute nitric acid?
Concentrated: brown nitrogen dioxide (NO₂). Dilute: colourless nitric oxide (NO), which turns brown in air
How is the nitrate ion detected?
The brown ring test: add freshly prepared iron(II) sulphate solution, then pour concentrated sulphuric acid carefully down the side of the tube; a brown ring forms where the liquids meet
1. Write the equation for the laboratory preparation of nitric acid from sodium nitrate.
2. Why is an all-glass apparatus used?
3. Why does concentrated nitric acid turn yellow on standing?
4. Name the catalyst used in the Ostwald process.
5. Which gas forms when copper reacts with concentrated nitric acid?
6. Which gas forms when copper reacts with dilute nitric acid?
7. What mass of HNO₃ can be obtained from 85 g of NaNO₃?
8. Name the test used to detect nitrates.
9. Name the products when carbon is heated with concentrated nitric acid.
10. Why does nitric acid not usually liberate hydrogen with metals?