This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Surface Chemistry – Colloids”.
1. Which of the following colloidal system represents a gel?
a) Solid in liquid
b) Solid in gas
c) Liquid in solid
d) Liquid in gas
Explanation: A gel is a colloidal system in which the dispersed phase is a liquid and the dispersion medium is a solid. Toothpaste, jam, cheese, rubber and gelatin (animal protein) are some of the examples of colloidal systems which are gels.
2. How are colloidal solutions of gold prepared by different colours?
a) Different diameters of colloidal gold particles
b) Variable valency of gold
c) Different concentration of gold particles
d) Impurities produced by different methods
Explanation: Colloidal solutions of gold prepared by different methods are of different colours because of different diameters of colloidal gold particles. The colour of colloidal solutions depends upon the size of the colloidal particles.
3. What are the dispersed phase and dispersion medium in alcohol respectively?
a) Alcohol, water
b) Solid, water
c) Water, alcohol
d) Solid, alcohol
Explanation: A colloidal solution having alcohol as the dispersion medium and a solid substance as the dispersed phase is called an alcohol. For example: A colloidal solution of cellulose nitrate in ethyl alcohol is an alcohol.
4. What is the range of the size of colloidal particles?
a) 1 to 100 nm
b) 10 to 100 pm
c) 1 to 100 µm
d) 1 to 10 mm
Explanation: A colloid is typically a two-phase system consisting of a continuous phase (the dispersion medium) and dispersed phase (the particles or emulsion droplets). The particle size of the dispersed phase typically ranges from 1 nanometre to 1 micrometre.
5. By using what can the colloidal particles can be separated from particles of true solution?
a) Parchment paper
b) An ultracentrifuge machine
c) An electrolyte
d) Ordinary cloth
Explanation: Centrifugation is a process which involves the use of the centrifugal force for the sedimentation of heterogeneous mixtures with a centrifuge used in industry and in laboratory settings. This process is used to separate two immiscible liquids. Particles of colloids are big enough to be blocked by parchment paper or animal membrane.
6. What isthe order of diameter of colloidal particles?
a) 10-3 m
b) 10-6 m
c) 10-15 m
d) 10-7 m
Explanation: Colloidal state of matter is, therefore, a state in which the size of the particles is such (1 to 1000 nm) that they can pass through filter paper but not through animal or vegetable membrane. Thus, every substance can be brought into the colloidal state by adopting suitable methods.
7. Dust is a colloid.
Explanation: Yes, the statement is true. Dust is a colloid if suspended in the air. It consists of a solid in a gas which is present in the atmosphere and it comes under the category of aerosols (contains small particles of liquid or solid dispersed in a gas).
8. When hit by light, what happens to a colloidal mixture?
d) Passes through
Explanation: When light strikes a colloidal mixture, it is reflected off the large particles and spreads out. It is so because the colloidal particles move rapidly and randomly. This is what happens when light hits a mixture.
9. Under which category is colloidal system?
a) Homogeneous mixture
b) Heterogeneous mixture
d) True solution
Explanation: Colloidal sols form heterogeneous mixtures consisting of particles of dispersed phase and the dispersion medium. The dispersed particles are spread evenly throughout the dispersion medium, which can be a solid, liquid, or gas.
10. What is the colloidal solution of a gas in liquid called?
Explanation: Depending upon whether the dispersed phase and the dispersion medium are solids, liquids or gases, eight types of colloidal systems are possible. The colloidal solution wherein gas is the dispersed phase and liquid is the dispersion medium is called foam.
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