Class 12th

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Ans: The process of physisorption for example that of H2 on finely divided nickel, involves weak van there Waals' forces. With increase in temperature, hydrogen molecules dissociate into hydrogen atoms which are held on the surface by chemisorption.

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Ans: River water is a colloidal solution of clay and sea water contains lot of electrolytes. The point at which river and sea meet is the site for coagulation. Deposition of coagulated clay results in delta formation.

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Ans: Activated charcoal acts as an adsorbent for various poisonous gases present in the coal mines.

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Ans: Eosin is adsorbed on the surface of silver halide precipitate making it coloured.

This is a Short Answers Type Questions as classified in NCERT Exemplar

Ans: Due to excessive dialysis, traces of electrolyte which stabilises the colloids is removed completely, making the colloid unstable. As a result, coagulation takes place.

This is a Short Answers Type Questions as classified in NCERT Exemplar

Ans: Physisorption involves weak van there Waals forces which weaken with rise in temperature. The chemisorptions involves formation of chemical bond involving activation energy and like any other chemical reaction is favoured by rise in temperature.

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Ans: The adsorption of positively charged Fe³⁺ ions by the sol of hydrated ferric oxide results in positively charged colloid.

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Ans: Moist alum coagulates the blood and so formed blood clot stops bleeding.

This is a Short Answers Type Questions as classified in NCERT Exemplar

Ans: Minimum quantity of an electrolyte required to cause precipitation of a sol is called its coagulating value. Greater the charge on flocculating ion and smaller is the amount of electrolyte required for precipitation, higher is the coagulating power of coagulating ion (Hardy-Schulze rule).

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Ans: On adding dispersion medium, emulsions can be diluted to any extent. The dispersed phase forms a separate layer if added in excess.