OXYGEN
The element Oxygen has atomic numbers 8 and an atomic mass of 16 amu. Its electronic configuration is 1s2, 2s22p4. The last electron is being added to the 2p-shell, therefore it belongs to the p-block of the periodic table.Oxide
The binary compound of Oxygen with the less electronegative element in the periodic
table is called an oxide. For example MgO, CO2, CO, CaO, etc.
Classification
of Oxide
On the basis of Chemical behavior oxides
1. Basic
oxide: Generally, metallic oxides which react with acids to form salt and
water are called basic oxides. Examples: Na2O, K2O, MgO,
FeO, CaO, etc.
Na2O + H2SO4 -----------»
Na2SO4 + H2O
2. Acidic
oxide: Generally, the non-metallic oxides which react with a base to form
salt and water are called acidic oxides. Example: CO2, SO2,
SO3, NO2, etc.
CO2 +
2NaOH -----------» Na2CO3 + H2O
3. Neutral oxide: These oxides neither react
with acids nor with a base to form salt and water. Example: H2O, CO,
NO, etc.
4. Amphoteric oxide: These oxides react with
both acid and base to form salt and water showing dual character. Example: ZnO,
Al2O3, SnO2, PbO2, etc.
ZnO + H2SO4 -----------»
ZnSO4 + H2O
ZnO + NaOH -----------» Na2ZnO2 +
H2O
5. Peroxide: The oxide which contains
more oxygen than the demand of molecular formula and has oxidation no. of
oxygen as (-1) is called peroxide. Example: H2O2, K2O2,
Li2O2,etc.
6. Mixed oxide: The oxide formed by the combination of two or more simple oxides of an element is called mixed oxide.
Ozone(O3 )
It is
elemental oxygen that exists as a tri-atomic molecule in addition to oxygen.
Naturally, Ozone is produced in the
stratosphere due to the addition of UV rays over molecular Oxygen gas.
O2 ---UV-Rays----»
O + O
[O2 + O
-----------» O3]*2
.
3O2 ------UV rays----» 2O3
Properties
of ozone
- It has
pale blue color in gas and deep blue color in solution
- It is
slightly heavier than air
- It is
slightly soluble in water but highly soluble in turpentine oil
- It has an unpleasant fishy odour
- It is a
powerful oxidizing agent and can oxidize PbS into PbSO4
[
O3 -----------» O2 +
O ] * 4
PbS + 4O -------» PbSO4
.
PbS
+ 4O3-----------» 4O2 +PbSO4
Tailing
of Mercury
when mercury is exposed to ozone gas, it stricks to the wall of a glass
tube, losing its meniscus by forming a black stain like a tail. The phenomenon
is called the tailing of mercury. It is due to the formation of mercurous oxide (
Hg2O ).
O3
-----------» O2 + O
2Hg + O ---------» Hg2O
.
2Hg
+ O3 -----------» Hg2O + O2
Uses of
Ozone
- It is
used as an oxidizing agent
- It is
used as germicides, disinfectant, and air refresher
- It is
used to carry out ozonolysis reactions in organic chemistry
Depletion
of the Ozone layer
Through
CO2 and CH4 are partly responsible for the
depletion of the ozone layer, the main causative agent is Chlorofluorocarbon
molecules ( CFCs) generated from refrigerator and aerosols.
The
probable mechanism of ozone layer depletion by CFcs :
CFCl3------ -UV-Rays---»
CFCl2 + Cl
O3 + Cl -----------»
ClO + O2
ClO ------uy--rays---»
Cl + O
O + O3 -----------»
2O2
CFCs is
decomposed by UV rays to produce chlorine-free radical which attacks ozone
molecule to form ClO. ClO is decomposed by UV rays and free radical is
regenerated which can attack another ozone molecule. In this way, a single
molecule of CFCs can destroy thousands of ozone molecules through this
chain mechanism called depletion and hole in the ozone layer.
Some of the ideas for the prevention of ozone layer depletion
- The excessive use of CFCs in
refrigerators and aerosols should be reduced
- The emission of CO2 and
CH4 gases in the environment should be checked
- Alternative gas should be developed in place of CFCs
- Public awareness should be raised
