21. In a colloidal sol, which of the following forces stabilize the colloidal particles?
- a) Gravitational forces
- b) Electrostatic repulsion
- c) Magnetic forces
- d) van der Waals forces
Answer: b) Electrostatic repulsion
Explanation: Colloidal particles are stabilized primarily by electrostatic repulsion. The particles carry like charges, which prevent them from coming together and aggregating.
22. Which of the following is an example of an aerosol?
- a) Fog
- b) Butter
- c) Rubber
- d) Milk
Answer: a) Fog
Explanation: An aerosol is a colloidal system where a liquid is dispersed in a gas. Fog consists of tiny water droplets dispersed in air, making it an example of an aerosol.
23. The method used to separate colloidal particles from impurities is:
- a) Coagulation
- b) Electrophoresis
- c) Ultrafiltration
- d) Sedimentation
Answer: c) Ultrafiltration
Explanation: Ultrafiltration is a technique used to separate colloidal particles from impurities based on particle size. It employs special filters with very fine pores that allow small impurities to pass through but retain colloidal particles.
24. The process by which a colloidal sol is converted into a gel is known as:
- a) Peptization
- b) Gelation
- c) Coagulation
- d) Electrolysis
Answer: b) Gelation
Explanation: Gelation is the process by which a colloidal sol is converted into a gel. It involves the formation of a three-dimensional network that traps the dispersion medium, giving the colloid a semi-solid structure.
25. Which of the following is true for a lyophilic colloid?
- a) It can be easily precipitated
- b) It has a strong affinity for the dispersion medium
- c) It is unstable
- d) It cannot be easily prepared
Answer: b) It has a strong affinity for the dispersion medium
Explanation: Lyophilic colloids have a strong affinity for the dispersion medium (such as water), making them easy to form and relatively stable compared to lyophobic colloids.
26. When an electrolyte is added to a colloidal sol, the colloidal particles tend to:
- a) Coagulate
- b) Become more stable
- c) Exhibit Brownian motion
- d) Increase in size
Answer: a) Coagulate
Explanation: Adding an electrolyte to a colloidal sol neutralizes the charges on the colloidal particles, causing them to aggregate and settle down as a precipitate, leading to coagulation.
27. The gold number is an indicator of:
- a) The size of colloidal particles
- b) The stability of a colloid
- c) The color of colloidal solutions
- d) The type of colloid formed
Answer: b) The stability of a colloid
Explanation: The gold number indicates the amount of a protective colloid required to prevent the coagulation of a gold sol when an electrolyte is added. A lower gold number indicates a more effective protective colloid, and hence, a more stable colloidal solution.
28. Brownian movement in colloids is due to:
- a) Gravitational forces
- b) Intermolecular collisions
- c) Random collisions of molecules of the dispersion medium with the colloidal particles
- d) Attractive forces between colloidal particles
Answer: c) Random collisions of molecules of the dispersion medium with the colloidal particles
Explanation: Brownian movement is the random, zig-zag motion of colloidal particles due to the continuous bombardment of the particles by the molecules of the dispersion medium.
29. Which of the following will not coagulate a colloidal sol?
- a) Adding a suitable electrolyte
- b) Boiling the sol
- c) Adding an oppositely charged colloid
- d) Cooling the sol
Answer: d) Cooling the sol
Explanation: Coagulation of colloidal sols occurs by adding an electrolyte, heating the sol, or adding an oppositely charged colloid. Cooling a sol does not cause coagulation, as it doesn’t affect the charge or movement of particles significantly.
30. In a colloidal system, the particles of the dispersed phase can be separated by:
- a) Filtration
- b) Centrifugation
- c) Decantation
- d) Evaporation
Answer: b) Centrifugation
Explanation: The particles of the dispersed phase in a colloid are small enough to pass through normal filters but can be separated by centrifugation, a process in which rapid spinning separates particles based on their size and mass.
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