Q14 of 26 Page 1

Give reason for following observation:

(i) Physisorption decrease with increase in temperature.


(ii) Addition of alum purifies the water.


(iii) Brownian movement provides stability to colloidal solution.


(i) in physisorption the molecules bounded to surface by weak vander wall forces , due to which on attaining high temperature, their bonds start breaking, they start escaping from surface, resulting in decrease in physisorption.

(ii) The alum on addition in water, coagulates the fine suspended particles present in water and flocculate them. The flocculated particles are large enough to be easily removed. Hence, it purifies the water.


(iii) The Brownian movement acts against the gravitational force of earth and hence don’t let the sol particles settled down and get coagulated. And imparts stability to sol.


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2MnO4- + 6H+ + 5 S032-→