Answer:
Physical adsorption is an exothermic process but its
enthalpy of adsorption is very low (20-40 kJ ) and is
smaller than that of chemisorption. In physical adsorption, attraction between
gas molecules (adsorbate) and solid surface (adsorbent) is very weak due to van
der Waals' forces. But in case of chemisorption, adsorption is due to new bond
formation hence heat of adsorption is very high. [1]
(b) Cellulose nitrate is peptised by organic solvents such
as ethyl alcohol and the product is called colloidion. [1]
(c)
Peptisation
Coagulation
Peptisation
involves conversion of a freshly formed ppt (such as AgCI, , into
sol by the addition of 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 adsorption of the common ion of the
electrolyte and the precipitate to be dispersed Aal is oeotised bv Kl or
Coagulation
involves Conversion of a colloidal sol into suspended (ppt) state.
Coagulation can take
place by addition of suitable electrolyte. Greater the charge on the ion
(of electrolyte) greater the coagulating power to coagulate ppositely
charged colloidal sol. is
coagulated byandion
and coagulating power is in order
by Hardy-SchuIze
rule.
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