14.0 NITROGEN AND ITS COMPOUNDS

Nitrogen makes up about 78% of the air we breathe, yet it is essential for life and incredibly useful in industry. From the ammonia that fertilizers are made from, to the nitric acid used in explosives, nitrogen compounds are everywhere. This chapter explores how we obtain nitrogen, the chemistry of ammonia and nitric acid, and the environmental challenges posed by nitrogen-based fertilizers.

14.1 ISOLATION OF NITROGEN FROM AIR

Air is a mixture of gases, primarily nitrogen (78%) and oxygen (21%). To obtain pure nitrogen, we need to separate it from the other components, especially oxygen.

14.1.1 Laboratory Preparation of Nitrogen from Air

In the lab, nitrogen can be prepared by removing oxygen from air using a chemical reaction.

• Method: Air is passed over heated copper turnings. Copper reacts with oxygen to form solid copper(II) oxide, leaving nitrogen gas (along with noble gases like argon) behind.
• Equation: 2Cu(s) + O₂(g) → 2CuO(s)
• Procedure:
  1. Air is slowly passed through a hard glass tube containing copper turnings heated strongly.
  2. The oxygen is absorbed by the copper, which turns black as copper oxide forms.
  3. The gas collected at the end is mainly nitrogen, with traces of noble gases (argon, neon, etc.). It may also contain carbon dioxide and water vapour, which can be removed by passing through soda lime and a drying agent if very pure nitrogen is required.
• Limitation: Th