Air and oxygen

4.3 Polymers

5.2 Water

Air and oxygen

  1. Composition of air

    1. Air is a mixture of gases with different boiling points
    2. It is approximately composed, by volume, of 78.1% nitrogen and 20.9% oxygen with relatively small amounts of argon, carbon dioxide and neon: 0.94%, 0.04% and 0.002% respectively, as well as a variable amount of water vapour depending on the position above Earth, ranging from 0.001% to 5%
    3. Dry air without carbon dioxide can be liquefied and then fractionally distilled to obtain oxygen and nitrogen

  2. Combustion

    1. Oxidation & reduction reactions involve the addition & removal of oxygen respectively
    2. When substances burn in air, they are reacting with the oxygen
    3. Elements can burn in air to form oxides, which can be classified as acidic, basic or amphoteric, which means they can react as an acid or a base
    4. Metal oxides are basic; non-metal oxides are acidic

    5. Specific elements:

      1. Sodium burns with an orange glow or flame depending on the size of the piece, forming a solid mixture of white sodium oxide and yellow-white sodium peroxide
      2. Magnesium burns with a blinding white light, forming white solid magnesium oxide
      3. Iron burns brilliantly, giving off bright sparks of the burning metal and forming Iron (III) oxide
      4. Carbon burns vigorously, forming carbon dioxide and a little carbon monoxide
      5. Sulfur burns with a bright blue flame and melts into a blood-red liquid, forming colourless sulfur dioxide, a pungent gas, and a little sulfur trioxide