1.      In air, 21% by volume.
2.      In water, 89%, and dissolved in it.
3.      In metal and non-metal oxides.


Lab method

1.      Heating of metal oxides
2Ag2O Δ4Ag + O2
2HgO Δ2Hg + O2
2Pb3O4 Δ6PbO + O2
2PbO2 Δ2PbO + O2
2.      Heating hydrogen peroxide
2H2O2 Δ (MnO2) 2H2O + O2↑
3.      Heating of potassium chlorate
2KClO3 Δ2KCl + 3O2

4.      Reaction of water and sodium peroxide.
2Na2O2 + H2O4NaOH + O2


1.      From air – dust is removed by filters, CO2 is removed by potassium hydroxide and water is removed by a drying agent. Air is liquefied by compression and cooling. When warmed, liquid nitrogen boils away first (-196°C) and liquid oxygen next (-183°C). It is stored in cylinders.
2.      From water – the electrolysis of water yields oxygen at the anode.



1.      It is a colorless, odorless, tasteless, neutral gas.
2.      It is slightly soluble in water, and slightly heavier than air.
3.      It boils at -183°C.


  1. It does not burn, but supports combustion.
  2. It forms oxides.
    1. Acidic oxides – or acid anhydrides, combine with water to form acids.
S + O2SO2 then SO2 + H2OH2SO3
C + O2CO2 then CO2 + H2OH2CO3
4P + 5O22P2O5 then P2O5 + 3H2O2H3PO4
These react with bases:
SO2 + NaOHNa2SO3 + H2O
CO2 + NaOHNa2CO3 + H2O
P2O5 + 6NaOH2Na3PO4 + 3H2O
    1. Basic oxides – are oxides of metals – they react with acids
MgO + H2SO4MgSO4 + H2O
Fe2O3 + 6HCl2FeCl3 + 3H2O
CaO + H2SO4CaSO4 + H2O
Some basic oxides react with water to form alkalis
Na2O + H2O2NaOH
CaO + H2OCa(OH)2
    1. Neutral oxides – for example, H2O, CO, NO, etc.
    2. Amphoteric oxides – act as both acids and bases.
ZnO + H2SO4ZnSO4 + H2O
ZnO + 2NaOHNa2ZnO2 + H2O
  1.  Oxygen oxidizes lower oxides                    
2NO + O2 (Pt)2NO2
2SO2 +  O22SO3
2CO + O22CO2
  1.  Oxidation
2H2S + 3O22H2O + 2SO2
CH4 + 2O2CO2 + 2H2O
2ZnS + 3O22ZnO + 2SO2
4NH3 + 5O2 (Pt, 800°C)4NO + 6H2O

Confirmatory Tests

  1. It rekindles a glowing splint
  2. In contact with colorless nitric oxide, it produces reddish-brown fumes of nitrogen dioxide
  3. It is absorbed by a solution of pyrogallol, which turns brown


  1. For respiration
  2. In medicine
  3. In oxy-acetylene torch
  4. In iron and steel production, to remove impurities
  5. In explosives
  6. In rockets, liquid oxygen is used for combustion

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