Here below some basic MCQ’s about “Colloids and Emulsions” with answer explanation for practice and exam preparation. Let’s check one by one.
1. Which of the following is an example of a colloidal solution?
- a) Sugar solution
- b) Salt solution
- c) Milk
- d) Glucose solution
Answer: c) Milk
Explanation: Milk is an example of a colloidal solution, specifically an emulsion, where liquid fat globules are dispersed in water. In contrast, sugar, salt, and glucose solutions are true solutions, not colloids.
2. The dispersed phase in a colloidal solution of smoke is:
- a) Solid
- b) Liquid
- c) Gas
- d) Plasma
Answer: a) Solid
Explanation: Smoke is an example of a solid dispersed in a gas. The solid particles (soot, ash) are suspended in the gas (air).
3. Which of the following is an example of a lyophilic colloid?
- a) Starch
- b) Ferric hydroxide
- c) Gold sol
- d) Sulphur sol
Answer: a) Starch
Explanation: Lyophilic colloids are colloids that have an affinity for the solvent, meaning they are easily formed. Starch is a lyophilic colloid because it can readily form a colloidal solution in water. Ferric hydroxide, gold sol, and sulphur sol are examples of lyophobic colloids, which have little affinity for the solvent and are less stable.
4. Which one of the following methods is not suitable for the purification of colloidal solutions?
- a) Dialysis
- b) Ultrafiltration
- c) Electrophoresis
- d) Cottrell precipitator
Answer: d) Cottrell precipitator
Explanation: The Cottrell precipitator is used to remove smoke particles from industrial gases and is not used for the purification of colloidal solutions. Dialysis, ultrafiltration, and electrophoresis are suitable methods for the purification of colloids.
5. Tyndall effect is observed in:
- a) True solutions
- b) Suspensions
- c) Colloidal solutions
- d) Both true solutions and colloidal solutions
Answer: c) Colloidal solutions
Explanation: The Tyndall effect is the scattering of light by colloidal particles when light passes through a colloidal solution. True solutions do not show the Tyndall effect, as the particles are too small to scatter light. Suspensions may scatter light, but they are not stable systems like colloids.
6. An emulsion is a colloidal system in which:
- a) Gas is dispersed in liquid
- b) Liquid is dispersed in another liquid
- c) Solid is dispersed in gas
- d) Solid is dispersed in liquid
Answer: b) Liquid is dispersed in another liquid
Explanation: An emulsion is a colloidal system where tiny droplets of one liquid are dispersed in another liquid with which it is immiscible. For example, milk is an emulsion where fat is dispersed in water.
7. Which of the following stabilizes an emulsion?
- a) Surfactants
- b) Electrolytes
- c) Alcohol
- d) None of the above
Answer: a) Surfactants
Explanation: Surfactants, also known as emulsifying agents, stabilize emulsions by reducing the surface tension between the dispersed phase and the dispersion medium, preventing the droplets from coalescing.
8. Which of the following types of colloids is a gel?
- a) Aerosol
- b) Foam
- c) Sol
- d) Jelly
Answer: d) Jelly
Explanation: A gel is a type of colloid in which the dispersed phase is a solid and the dispersion medium is a liquid. Jelly is a common example of a gel, where a semi-solid structure is formed.
9. Which of the following processes is used to coagulate a colloidal solution?
- a) Addition of electrolytes
- b) Heating
- c) Addition of oppositely charged colloid
- d) All of the above
Answer: d) All of the above
Explanation: Coagulation of a colloidal solution can be brought about by adding electrolytes, heating the solution, or mixing it with an oppositely charged colloid. These processes neutralize the charge on the colloidal particles, leading to aggregation and settling.
10. Gold sol is an example of:
- a) Lyophobic colloid
- b) Lyophilic colloid
- c) Emulsion
- d) Aerosol
Answer: a) Lyophobic colloid
Explanation: Gold sol is a lyophobic colloid, meaning it does not have a strong affinity for the solvent and requires stabilization. Lyophobic colloids are less stable and more difficult to prepare than lyophilic colloids.
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