Oxygen compounds of nitrogen
Nitrogen forms oxides with oxygen: N₂O (+1), NO (+2), N₂O₃ (+3), NO₂ (+4), N₂O₅ (+5); nitrogen does not combine with oxygen under ordinary conditions, so they are made indirectly. NO is a colourless gas, hardly soluble in water, a non-salt-forming (neutral) oxide. It forms in air during lightning (N₂ + O₂ ⇌ 2NO – Q), is made in industry by oxidizing ammonia over a catalyst, and in the laboratory by acting on copper with dilute nitric acid (3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O). In air NO at once turns into reddish-brown NO₂: 2NO + O₂ → 2NO₂. NO₂ is a sharp-smelling, poisonous, choking gas and an acidic oxide; in water it gives nitric and nitrous acids: 2NO₂ + H₂O → HNO₃ + HNO₂, and with oxygen 4NO₂ + 2H₂O + O₂ → 4HNO₃. NO₂ is in equilibrium with its dimer N₂O₄. Car engines and thermal power stations release nitrogen oxides into the air; they are one cause of acid rain and city smog. N₂O (“laughing gas”) is used for anaesthesia in medicine, but only by specialists. Working with nitrogen oxides is dangerous, so experiments are done only by the teacher in a fume cupboard.
“Nitrogen ladder”: write the nitrogen oxide formulas as a ladder in order of oxidation state, N₂O … N₂O₅. Add colour, state (gas) and hazard sign on each rung. Write 3 ways to reduce exhaust gases in traffic (public transport, catalytic converter, electric cars).