Explain the following observations: (a) Ferric hydroxide sol gets coagulated on addition of sodium chloride solution (b) Cottrell’s smoke precipitator is fitted at the mouth of the chimney used in factories. (c) Physical adsorption is multilayered, while chemisorption is monolayered.

(a)The reaction forms an insoluble preceiptate of ferric chloride, FeCl3 (s). The net reaction can be shown as:
Fe3+(aq) + 3CL-(aq) ----> FeCl3(s)
(b)to get smoke free of charged particle we are using cottrell’s smoke precipitator as the smoke coming out of chimney has charged particle of carbon so to neutralise it a oppositely charged plate called cottrells smoke precipitator is used
(c)physisorption involves van der wall attractive forces between adsorbent and adsorbed , This may result on the accumulation of many layers of the molecules on the surface.Chemosorption involves formation of chemical bonds between adsorbent and adsorbed molecule