Answer:
(i) Peptisation Peptisation involves conversion of
a freshly formed precipitate (such as AgCl, Fe(OH)3, Al (OH)3) into
a sol by the addition of a small amount of a suitable electrolyte. An
electrolyte having an ion in common with the material to be dispersed is required
for sol formation. The peptisation action is due to preferential adsoprtion of
the common ion of the electrolyte and the precipitate to be dispersed.
As a result of
preferential adsorption of the common ion, particles acquire a positive or
negative charge depending on the charge on the ion adsorbed.
Because of
the presence of the same type of charge, the particles of the precipitate are
pushed apart and get dispersed forming a stable colloidal sol.
Agl is
peptised by addition of 
as
common ion)
or KI (
as
common ion).
(
is
adsorbed)
(
is
adsorbed
Ferric
hydroxide sol is formed by the addition of
solution
to the freshly formed precipitate of 
which
adsorbs 
and thus
stable sol is formed.
Similariy,
an aluminium hydroxide sol is formed when dilute hydrochloric acid is added to
freshly precipitated aluminium hydroxide. This is due to adsorption of 
on 
is formed
first by action of 
on
[1]
(ii)
Effect of temperature on chemisorptions Adsorption is a
spontaneous change 
taking
place with decrease in entropy.
and to
make 
should
be negative. Thus adsorption is exothermic change. By Le-Chatelaine principle,
increase in temperature should decrease extent of adsorption, but in chemisorptions,
there is first increase and then decrease in adsorption.
(iii)
Associated colloids There are certain colloids which behave as normal
strong electrolytes at low concentrations but exhibit colloidal properties at higher
concentrations due to formation of aggregated particles. These are called
associated colloids (micelles).
Examples
Surface active agents like soap, detergents.
Soap is 
In
aqueous solution ,there is formation of 
and 
. In oily
matter (say grease) washing with detergent soap/(R-hydrophobic)
goes into oil and forms associated colloids, [1]
You need to login to perform this action.
You will be redirected in
3 sec
