Chemistry NCERT Exemplar Solutions Class 12th Chapter Five

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

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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.

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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.

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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.

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Ans: In Cottrell precipitator, charged smoke particles are passed through a chamber containing plates with charge opposite to the smoke particles. Smoke particles lose their charge on the plates and get precipitated.

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Ans: Animal hide is colloidal in nature and has positively charged particles. When it is soaked in tannin which has negatively charged colloidal particles, it results in mutual coagulation taking place.

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Ans: Medicines are more effective in the colloidal form because of large surface area and are easily assimilated in this form.