Question

Select the incorrect statement related to colloids.

• A. Muddy water can be coagulated more effectively by alums as compared to $NaCl$
• B. Surface tension of lyophilic colloids is less than that of dispersion medium
• C. When excess of $AgN{O}_3$ is added in aqueous $KI$ solution and the sol is subjected to electrophoresis, coagulation occurs near the anode
• D. Cloud bursting in atmosphere occurs due to large amount of water present in the cloud

Answer 1

Answer: (C), (D)

Cloud bursting in atmosphere occurs due to large amount of water present in the cloud

The coagulation power of alum $(K_{2}S{O}_4.A{l}_2(S{O}_4{)}_3.24H_{2}O)$ is greater than that of $NaCl$ due to the presence of higher charge on alum. Therefore, muddy water can be coagulated more effectively by alums as compared to $NaCl$. Hence option (a) statement is correct.

Lyophilic sols are those where the substances have a high affinity for the dispersion medium and thus easily form colloidal solutions. As they are highly hydrated, the viscosity decreases, and so they have a lower surface tension than the dispersion medium. Hence option (a) statement is also correct.

When a dilute solution of potassium iodide is added to a slight excess of a dilute solution of silver nitrate, a positive charged sol of silver iodide is formed. It is due to the adsorption of Ag+ ions from the dispersion medium on the precipitate of silver iodide (AgI). Therefore, during electrophoresis coagulation occurs near the cathode. Hence, option (c) statement is incorrect.

Cloud is a colloidal solution in which water is a dispersed phase and air is the dispersion medium. Cloud bursting happens when oppositely charged clouds come in contact. Hence, option (d) statement is also incorrect.