Nitrogen

Preparation

Nitrogen is prepared by heating ammonium nitrite.

NH₄NO₂N₂↑ + 2H₂O

Properties

• Colourless tasteless, odourless neutral gas.
• Highly inert
• Neither combustible nor supporter of combustion however a burning piece to Mg continues to burn in nitrogen. The product formed on hydrolysis gives NH₃.

3Mg + N₂Mg₃N₂↓
Mg₃N₂ + 6H₂O 3Mg(OH)₂ + 2NH₃↑

Uses

• Used in the manufacture of ammonia nitric acid, cynamide etc.
• Nitrogen filled thermometers are used for measuring high temperature.
• Liquid N₂is used as a refrigerant to preserve biological materials.

Compounds of Nitrogen

Oxyacids
The most important oxo-acid of nitrogen is nitric acid HNO₃

Preparation

• In the lab, it is prepared by heating NaNO₃ or KNO₃with conc. sulphuric acid in a glass retort.
  NaNO₃ + H₂SO₄ →NaHSO₄ + HNO₃
• It is manufactured by the catalytic oxidation of ammonia and the process is known as Ostwald Process
  4NH₃ + 5O₂ 4NO + 6H₂O
  2NO + O₂2NO₂
  3NO₂ + H₂O → 2HNO₃ + NO.

Properties

• In aq. solution, nitric acid is a strong acid and dissociates to give hydronium and nitrate ions. HNO₃ + H₂O H₃O₊ + NO₃^-
• Action on metals: Conc. nitric acid is a strong oxidising agent and attacks most of the metals except noble metals such as gold and platinum. The product of reaction depends upon the concentration of the acid, temp and the nature of the material undergoing oxidation. With dilute nitric acid the principle product is nitric oxide NO and with conc. nitric acid,  the principle product is N(IV) oxides 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O           (dilute)
  Zinc, which is a more powerful reducing agent than copper, reacts with dilute nitric acid to give ammonium nitrate.
  4Zn + 10HNO₃ → 4Zn(NO₃)₂ + NH₄NO₃ + 3H₂O
  Nitric acid also oxidises non - metals and their compounds. Iodine is oxidised to iodic acid, carbon to carbon dioxide, sulphur to H₂SO₃ and phosphorus to phosphoric acid. Nitric acid is reduced to nitrogen dioxide (NO₂).
  I + 10HNO₃ → 2HIO₃ 10NO₂ + 4H₂O
  C + 4HNO₃ → CO₂ + 2H₂O + 4NO₂
  1/8 S₈ + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O
  P₄ + 20HNO₃ → 4 H₃PO₄ + 20NO₂ + 4H₂O