Questions and Answers of Surface Chemistry
Q1. What is fire foam?
A1. Carbon dioxide froth made by mixing solutions of sodium bicarbonate and alum is called fire foam. It is used in fire extinguishers. A protective colloid such as glue or dextrin is added to stabilise the foam.
Q2. What is the Difference between aqua dag and oil dag?
A1. Aqua dag is a colloidal solution of graphite in water while oil dag is a colloidal solution of graphite in oil.
Q3. What is meant by adsorption?
A3. It is the phenomenon of higher concentration of a molecular species at the surface of a solid than in bulk.
Q4. What is meant by absorption?
A4. Absorption is the phenomenon of uniform distribution of a substance into the body of another substance.
Q5. What is Physical adsorption or physisorption?
A5. In this type of adsorption, molecules of adsorbate are being held to the solid surface by weak attractive forces called Vander Waals’ forces.
Q6. What is chemisorption?
A6. When the forces of attractive between adsorbate particles and adsorbent are almost of the same strength as chemical bond, the adsorption is called chemical adsorption or chemisorption.
Q7. What is desorption?
A7. It is the process which involves the removal of adsorbate from the surface of the adsorbent.
Q8. What is sorption?
A8. Process involving simultaneous adsorption and absorption is called sorption.
Q9. Define specific surface area?
A9. It is surface area in square meters per gram of the solid adsorbent which may be in the form of powder or porous mass.
Q10. What is occlusion?
A10. The adsorption of gases on the surface of metals is called occlusion.
Q11. What is saturation pressure?
A11. It is the pressure at which further increase of pressure does not cause further increase in the extent of adsorption.
Q12. What is Activated Charcoal?
A12. It is the charcoal treated with superheated steam to increase its absorption power.
Q13. What is meant by peptization?
A13. The process of converting a freshly prepared precipitate into colloidal solution by adding a suitable electrolyte is called Peptization.
Q14. What is Brownian movement?
A14. It involves the motion of colloidal particles in a zig-zag path.
Q15. Describe electrophoresis?
A15. It is a phenomenon in which colloidal particles move towards the oppositely charged electrodes in an electric field. For Example- As2S3 solution being negatively charged, the colloidal particles will move towards positive electrode.
Q16. Define the term “Tyndall effect”?
A16. When a strong beam of light is passed through a colloidal solution, the path of the light becomes visible when viewed from a direction at right angle to that of the incident light. This is due to the fact that solution particles absorb light energy and then scatter it in all direction.
Q17. What is coagulation process?
A17. The process by means of which the particles of the dispersed phase in a solution are precipitated is called coagulation. It is generally achieved by neutralizing the charge on colloidal particles by the addition of a suitable solvent.
Q18. What is demulsification?
A18. Demulsification is a process which involves the breaking down of an emulsion to yield constituent liquids. It can be brought about by-
- Boiling or Freezing or Centrifuging
- Adding a substance that destroys the emulsifier
- Adding a dehydrating agent in case
Q19. Why activated charcoal is better adsorbent than ordinary charcoal?
A19. Activated charcoal has a larger surface area than ordinary charcoal. Since adsorption is a surface phenomenon, activated charcoal is a better adsorbent than ordinary charcoal.
Q20. What is salting out?
A20. Lyophobic sols are easily precipitated by the addition of small amounts of electrolyte. Precipitation takes place due to neutralization of charge on colloidal particles and the process is called coagulation. The term ‘Salting Out’ is used for the precipitation of lyophilic sols.
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