41. Which of the following is not a method for the purification of colloids?
- a) Dialysis
- b) Electrophoresis
- c) Ultrafiltration
- d) Sublimation
Answer: d) Sublimation
Explanation: Sublimation is a process in which a solid turns into gas without passing through the liquid phase, and it is not used for the purification of colloids. Dialysis, electrophoresis, and ultrafiltration are all methods used for colloid purification.
42. Which of the following is not a characteristic of lyophobic colloids?
- a) They are irreversible
- b) They are stable in the presence of small amounts of electrolytes
- c) They are less stable than lyophilic colloids
- d) They are prepared by dispersion or condensation methods
Answer: b) They are stable in the presence of small amounts of electrolytes
Explanation: Lyophobic colloids are not stable in the presence of even small amounts of electrolytes, as the electrolytes tend to coagulate the colloid. Lyophilic colloids, on the other hand, are more stable in the presence of electrolytes.
43. Which of the following is an example of a colloidal system where the dispersed phase is a liquid and the dispersion medium is a gas?
- a) Emulsion
- b) Foam
- c) Aerosol
- d) Sol
Answer: c) Aerosol
Explanation: An aerosol is a colloidal system where the dispersed phase is a liquid, and the dispersion medium is a gas. Examples include fog and mist, where liquid water droplets are dispersed in air.
44. The formation of micelles occurs when the concentration of soap or detergent exceeds a certain threshold. This threshold is known as:
- a) Critical temperature
- b) Critical micelle concentration
- c) Coagulation point
- d) Peptization limit
Answer: b) Critical micelle concentration
Explanation: Micelles form when the concentration of soap or detergent in a solution exceeds the critical micelle concentration (CMC). Above this concentration, the soap molecules aggregate to form micelles, which help in the cleaning process.
45. Which of the following properties is shown by colloidal solutions but not by true solutions?
- a) Homogeneity
- b) Tyndall effect
- c) No settling of particles
- d) Ability to pass through normal filters
Answer: b) Tyndall effect
Explanation: Colloidal solutions show the Tyndall effect (scattering of light), which is not seen in true solutions because the particles in a true solution are too small to scatter light.
46. Which of the following is used for the purification of colloids by the process of diffusion?
- a) Ultrafiltration
- b) Dialysis
- c) Coagulation
- d) Centrifugation
Answer: b) Dialysis
Explanation: Dialysis is used for the purification of colloidal solutions by allowing the small impurities (ions, molecules) to pass through a semi-permeable membrane, while the larger colloidal particles are retained.
47. The stability of lyophilic sols is due to:
- a) Electric charge on colloidal particles
- b) Absorption of dispersion medium on the surface of colloidal particles
- c) Presence of electrolytes
- d) Peptization
Answer: b) Absorption of dispersion medium on the surface of colloidal particles
Explanation: Lyophilic sols are stable because of the strong affinity between the colloidal particles and the dispersion medium, which leads to the absorption of the medium onto the surface of the particles, preventing coagulation.
48. Which of the following will show maximum coagulating power for a negatively charged sol?
- a) NaCl
- b) BaCl₂
- c) AlCl₃
- d) KCl
Answer: c) AlCl₃
Explanation: According to Hardy-Schulze rule, the coagulating power of an ion increases with its charge. Since Al³⁺ carries a +3 charge, it will have a higher coagulating power for negatively charged sols compared to Na⁺ (+1), K⁺ (+1), and Ba²⁺ (+2).
49. Which of the following techniques is based on the difference in the size of particles for the purification of colloids?
- a) Ultrafiltration
- b) Electrophoresis
- c) Dialysis
- d) Peptization
Answer: a) Ultrafiltration
Explanation: Ultrafiltration is based on the difference in particle size. It involves passing the colloidal solution through filters with very fine pores, allowing smaller impurities to pass through while retaining the colloidal particles.
50. The color of a colloidal solution depends on:
- a) The nature of the dispersed phase only
- b) The size of the colloidal particles
- c) The temperature of the system
- d) The viscosity of the medium
Answer: b) The size of the colloidal particles
Explanation: The color of a colloidal solution depends on the size of the colloidal particles. As the particle size changes, the wavelength of light scattered by the particles also changes, leading to different colors.
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