Isolation of Oxygen & Compounds of Oxygen

Isolation of Oxygen & Compounds of Oxygen

Oxygen is pale blue gas having a strong characteristic smell. It is neutral to litmus


Isolation of Oxygen:

In laboratory it is prepared by heating  KMnO4 or KClO3 in presence of MnO2.

2KClO3 (s)  2KCl + 3O2

2KMnO K2MnO+ MnO2 + O2

It can also be prepared by reaction of H2O on Na2O2

2Na2O2 + 2H2O(l)  4NaOH + O2

On large scale it is prepared by fractional distillation of liquid air.

Pure oxygen is prepared by electrolysis of water.

Oxygen is also manufactured by

  1. Brine's Process:
    BaO is heated at 500C in air. It is converted into BaO2, which on further increase in temperature upto 800C decomposes to give oxygen.
     
  2. By electrolysis of water:
    Electrolysis is done by using alkaline water using nickel or platinum electrode which gives hydrogen and oxygen.
     

Compounds of Oxygen:

Ozone - O3
:

Preparation
:

It is prepared by subjecting pure oxygen to silent electric discharge

3O2  2O     H = + 284.5 kJ mole-1

Properties
:

It is pale blue gas having a strong characteristic smell. It is neutral to litmus.

  1. O3   O2 + O
     
  2. H2S + O  H2O + S
     
  3. 2Ag + O  Ag2O
     
  4. 2Hg + [O]  Hg2O
     
  5. l2 + H2O + 5[O]  2HIO3
     
  6. S + H2O + 3[O]  H2SO4
     
  7. 2P + 3H2O + 5[O]  2H3PO4
     
  8. It is better oxidising agent as compared to H2O2.

    H2O+ O H2O + 2O2

    BaO2 + O3  BaO + 2O2

    It is condensed to blue liquid (Boiling point 161.2 K)

    It condenses to a violet-black solid (m. pt 80.6 K), Ozone has angular structure. Both the O-O bonds are of equal bond length due to resonance.

     

Test of Ozone

In presence of O3, mercury loses its meniscus and starts sticking to glass. This is known as telling of mercury.

It does not release iodine from Kl in presence of FeSO4. In this way it is different from H2O2.


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