Hydrogen peroxide
Hydrogen peroxide was first prepared by L.J.Thenard, in 1813 by the action
of dilute acid on barium peroxide. Traces of H2O2 are found in atmosphere and
in certain plants.
Laboratory preparation
of hydrogen peroxide
1. By the action of dilute sulphuric acid on
sodium peroxide. Calculated quantity of Na2O2 is added in
small proportions to a 20% ice cold solution of sulphuric acid.
Na2O2 + H2SO4 --- > Na2 SO4 + H2O2
30% solution of H2O2 is obtained by this process.
2. Pure H2O2
is obtained by reacting BaO2 with an acid BaO2 + H2SO4 -- > Ba SO4 + H2O2
3BaO2 + 2H3 PO4 -- > Ba3 (PO4)2
+ 3H2O2
3. H2O2 is manufactured by followed by vacuum distillation. H2O2.
Reactions
H2SO4 -- > < --- H+ + HSO4-
2HSO4- -- > <
--- H2S2O8 + 2e-
(At anode)
H2S2O8 + H2O -- > < ---
H2SO4 + H2SO5
H2SO5 + H2O -- > < --- H2SO4
+ H2O2
2H+ + 2e- -- > < --- H2 (At cathode)
Concentration of
hydrogenperoxide solution
The impurities like organic material or metallic
ions, may catalyse its explosive decomposition.
1.
By careful evaporation of the solution obtained
above on a water bath preferably under reduced pressure using fractionating
column.
2.
By distillation under reduced pressure at
temperatures below 330K, the concentration up to 90% solution is used till crystallisation
formed.
Strength of
Hydrogenperoxide
The strength of a sample of hydrogen peroxide
solution is expressed in terms of the volumes of oxygen at S.T.P that one
volume of H2O2 gives on heating.
Properties
Physical
H2O2 is a colourless, odourless, syrupy liquid
in the anhydrous state. It is miscible with water, alcohol, and ether in all
proportions.
Chemical
Pure H2O2 is unstable and decomposes on standing.
On heating when water and oxygen are formed.
2H2O2 -- > 2H2O + O2
Oxidizing Properties
H2O2 is a powerful oxidizing agent. It functions
as an electron acceptor. H2O2 + 2H+ + 2e-
-- > 2 H2O
(In acidic solution)
H2O2- + 2e- -- > 2OH-
(In alkaline solution)
It
oxidises PbS to PbSO4
PbS+ 4H2O2 -- > PbSO4 +4H2O
It oxidizes ferrous salts int2Fe2+ + 2H+ + H2O2 --> 2 Fe3+ + 2H2O
Due to its oxidizing property, it is a valuable
bleaching agent, powerful but harmless disinfectant and germicide. Delicate
materials like silk, wool, hair which will be destroyed by chlorine, are
bleached with H2O2.
Reducing Properties
With powerful oxidizing agents, H2O2
acts as a reducing agent. Moist silver oxide, acidified KMnO4,
ozone, chlorine and alkaline solutions of ferricyanides are reduced.
Ag2O + H2O2 --> 2 Ag + H2O + O2
Uses
1.
It destroys bacteria and hence it is used as an
antiseptic and germicide for washing wounds, teeth and ears.
2.
It destroys the colour of some organic compounds
and is used in bleaching delicate things like hair, wool, silk ivory and
feathers.
3.
It is used as an oxidizing agent.
4.
It is also used as a propellant in rockets.o
ferric salts .
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