VERY SHORT ANSWER QUESTIONS (2 Marks Each)
Q.1. Why does extent of adsorption decrease with rise in temperature in case of physical adsorption?
Ans. With rise in temperature, the kinetic energy of the adsorbed particles increases. As a result, escaping tendency of these adsorbed particles from the surface of adsorbent increase. therefore the extent of adsorption decreases.
Q.2. What happens when a freshly precipitated Fe(OH)3, is shaken with a little amount of dilute solution of FeCl3?
Ans. Due to phenomenon of peptization, when a freshly prepared Fe(OH)3 is shaken with little amount of dilute solution of FeCl3 a reddish brown positively charged sol of ferric hydroxide is formed.
Q.3 State the principle of electrodialysis.
AnS. It is based upon the principle that ions can pass through parchment paper faster in electric field than colloidal particles and thus get separated.
Q.4 How are multimolecular colloids different from macromolecular colloids?
Ans. Multimolecular colloids consist of aggregation of small atoms or molecules as in sulphur and As2S3 sol while macromolecular colloids consist of large molecules as in starch sol or albumin sol.
Q.5 Lyophilic colloid is more stable than lyophobic colloid. Explain.
Ans. It is due to the reason that force of attraction between dispersed phase and dispersion medium is more in lyophilic colloids than in lyophobic colloids.
Q.6. What are micelles?
Ans. Associated colloids when dissolved in a medium behave as normal, strong electrolytes at low concentrations but at higher concentrations form aggregated particles caled micelles which exhibit the properties of colloidal state.
Q.7. Colloidal systems can be prepared in water and in air as media. what distinctive names are given to these two types of colloidal systems?
Ans. Colloidal systems with water as dispersion medium are called hydrosols or aquasols while with air as dispersion medium are called aerosols.
Q.8. What is meant by the term 'peptization°?
Ans. It is a process in which ionic solids tend spontaneously to break up into particles of colloidal size when a small amount of electrolyte containing a common ion is added to them.
Q.9. What are colloids?
Ans. Colloids are the heterogeneous solution which contain particles of intermediate size having diameters between 1 to 1000 nm. These particles cannot be seen by naked eye but can be seen under ultramicroscope which can pass through ordinary filter paper but not through animal membrane.
Q.10. What is adsorption?
Ans. The phenomenon of attracting and retaining any molecular species on the surface of a solid or a liquid giving rise to a higher concentration of the same species at the surface than in the bulk is known as adsorption.
Q.11. What is sorption?
Ans. When adsorption and absorption both occur simultaneously or when there is a doubt about whether absorption or adsorption is taking place, the term 'sorption' is used.
Q.12. What is meant by chemical adsorption?
Ans. When the adsorption is due to strong force of atraction similar to that of a chemical bond, it is called chemical adsorption. It results in the formation of a surface compound and is irreversible in nature.
Q.13. Why is adsorption exothermic?
Ans. Adsorption results in decrease in the residual forces acting along the surface of adsorbent. Consequently, there is a decrease of surface energy which appears as heat and the process of adsorption is exothermic.
Q.14. Define specific surface area.
Ans. Surface area of the solid in square metres per gram when the solid is in the form of powder or porous mass is called specific surface area.
Q15. Why does extent of chemical adsorption increases first and then decreases with rise in temperature?
Ans. Chemisorption involves activation energy. The initial increase in chemisorption is due to the fact the heat supplied acts as activation energy and, more and more molecules of adsorbate gain energy and possess energy greater than activation energy. Therefore, adsorption increases with increase in temperature. Further increases will increase the energy of the molecules adsorbed and will increase the rate of desorption. Therefore, extent of adsorption decreases.
Q.16. Why is it important to have clean surface in surface studies?
Ans. If the surface is not clean and is covered by the gases of air, then desired gases will not be able to be adsorbed on that surface.
Q.17. Why is chemisorption referred to as activated adsorption?
Ans. Chemisorption is due to chemical reaction between adsorbate and the adsorbent which requires energy. Because of this reason, it is known as activated adsorption.
Q.18. What type of solutions are formed on dissolving different concentrations of soap in water?
Ans. At low concentrations, soap forms a true solution in water. At concentration above cmc, it form a colloidal sol.
Q19. What happens when gelatin is mixed with gold sol?
Ans. Gelatin being a lyophylic sol when added to lyophobic gold sol protect the later which becomes stable.
Q20. How does it become possible to cause artificial rain by spraying silver iodide on the clouds?
Ans. Clouds contain charged colloidal water particles. On adding Agl which is an electrolyte, these colloidal particles get coagulated, form bigger particles which take the form of rain.
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