The Composition of Air

Air is a mixture of several gases. The main components are:

• Nitrogen (N₂): Makes up about 78% of the air. It's largely unreactive (inert).
  • Used in food packaging to keep food fresh.
  • Essential for plant growth (though plants can't use it directly from the air).
• Oxygen (O₂): About 21% of the air. It's vital for life and combustion.
  • All animals and humans need oxygen to breathe (respiration).
  • Things burn because of oxygen (supports combustion).
• Noble Gases: Around 0.94%, mostly Argon (Ar). Others include Neon (Ne), Helium (He), Krypton (Kr), Xenon (Xe).
  • Very unreactive, used in lighting (like neon signs, argon in light bulbs).
• Carbon Dioxide (CO₂): Approximately 0.04% (this value can vary slightly).
  • Plants use it for photosynthesis to make their food.
  • Released when we breathe out and when things burn.
• Other Gases and Impurities: About 0.02%, including water vapor, dust particles, and traces of other gases.

Discovering Air's Composition

Scientists like Antoine Lavoisier conducted experiments to understand what air is made of. He heated mercury and found it reacted with a part of the air (oxygen) to form a red powder, and this part was about 1/5th of the air.

A common experiment to show the percentage of oxygen in the air involves burning red phosphorus in a sealed container over water. The phosphorus uses up the oxygen, and water rises to fill the space, showing oxygen is about 1/5th (or 20-21%) of the air.