Bihar Board - Class 12 Chemistry - Chapter 5 Surface Chemistry Short Answer Question
The short question answers for Chapter 5: Surface Chemistry of Class 12 Chemistry are provided here in English. These questions are prepared based on the NCERT curriculum for Class 12. They will help students understand the chapter easily. These short question answers will be useful not only for the Class 12 board exams but also for entrance exams like NEET. The questions and answers for Bihar Board Class 12 Chemistry, Chapter 5: Surface Chemistry, have been prepared by expert teachers at Vidyakul.
Short Question Answer
Question 1. Define the term ‘Tyndall effect’.
Answer: Tyndall effect : When a beam of light is passed through a colloidal solution and viewed perpendicular to the path of the incident light, the path of light becomes visible as a bright streak. The illuminated path is called the Tyndall cone and the phenomenon is called the Tyndall effect.
Question 2. Define ‘electrophoresis’.
Answer: Electrophoresis : When electric current is passed through a colloidal solution, the positively charged particles move towards the cathode while negatively charged particles move towards anode where they lose their charge and get coagulated. The phenomenon is known as Electrophoresis.
Question 3. What are lyophobic colloids? Give one example for them.
Answer: Lyophobic sols : Substances like metals, their sulfides, etc., when simply mixed with the dispersion medium do not form the colloidal sol. Their colloidal sols can only be prepared by specific methods. They are not very hydrated and are irreversible in nature. They are also called extrinsic colloids.
Example : As2S3 sol.
Question 4. Out of NH3 and CO2 which gas will be adsorbed more readily on the surface of activated charcoal and why?
Answer: NH3 gas will be adsorbed more readily on activated charcoal. It has higher critical temperature than CO2 and is an easily liquefiable gas. Its van der Waals forces are stronger.
Question 5. How is a sol. different from an emulsion ?
Answer: A colloidal sol contains solid as the dispersed phase and liquid as the dispersion medium e.g. paint, gold sol etc.
Emulsion : A colloidal dispersion in which the dispersed- phase and the dispersion medium are immiscible liquids, is known as emulsion e.g. milk, butter etc
Question 6. Why is adsorption always exothermic?
Answer: Adsorption is accompanied by decrease of randomness. For the process to be spontaneous, G must be negative.
Hence, according to equation G =H-TS , G can be -ve only if H is negative.
Question 7. What are emulsions? Name an emulsion in which water is a dispersed phase.
Answer: Emulsions : An emulsion is a colloidal dispersion in which both the dispersed phase and dispersion medium are liquids.
Water in oil → Butter, cold creams.
Question 8. Which of the following is most effective in coagulating negatively charged hydrated ferric oxide sol?
(i) NaNO3 (ii) MgSO4 (iii) AlCl3
Answer:
AlCl3 (Aluminium chloride) is most effective in coagulating negatively charged hydrated ferric oxide sol.
Question 9: Describe some features of catalysis by zeolites.
Answer : Zeolites are alumino-silicates that are micro-porous in nature. Zeolites are also shape- selective catalysts as they have a honeycomb-like structure. Some silicon atoms are replaced by aluminum atoms in the extended 3D-network of silicates, giving them an Al-O-Si framework. The pores and cavity size of the zeolites makes the reactions very sensitive. Zeolites are commonly used in the petrochemical industry.
Question 10 : What is shape selective catalysis?
Answer: A catalytic reaction which depends upon the product molecules and on the size of the reactant and the pore structure of the catalyst is called shape-selective catalysis.
For example, catalysis by zeolites is a shape-selective catalysis. Thus, molecules having a pore size more than 260-740 pm cannot enter the zeolite and undergo the reaction.
Question 11. Name the two groups into which the phenomenon of catalysis can be divided. Give an example of each group with the chemical equation involved.
Answer:
Homogeneous catalysis : When the reactants and the catalyst are in the same phase, the process is called homogeneous catalysis.
Example : 2SO2 (g)+O2 (g) 2SO3 (g)
Heterogeneous catalysis : When the reactants and the catalyst are in different phases, the process is called heterogeneous catalysis.
Example : 2SO2 (g) 2SO3 (g)
Question 12. What is meant by coagulation of a colloidal solution? Describe briefly any three methods by which coagulation of lyophobic sols can be carried out.
Answer: The process of setting colloidal particles is called coagulation or precipitation of the sol. Methods of coagulation :
(1) By electrophoresis : The colloidal particles move towards oppositely charged electrodes.
(2) By mixing two oppositely charged sols.
(3) By addition of electrolytes : When excess of an electrolyte is added, the colloidal particles are precipitated.
Question 13. Describe a conspicuous change observed when
(i) a solution of NaCl is added to a sol. of hydrated ferric oxide.
(ii) a beam of light is passed through a solution of NaCl and then through a sol.
Answer: (i) Coagulation or precipitation of sol. takes place.
(ii) Scattering of light is observed when light is passed through a sol. whereas no scattering of light is observed in a solution of NaCl , Tyndall effect in the sol
Answer: Lyophobic sols : Substances like metals, their sulfides, etc., when simply mixed with the dispersion medium do not form the colloidal sol. Their colloidal sols can only be prepared by specific methods. They are not very hydrated and are irreversible in nature. They are also called extrinsic colloids.
Example : As2S3 sol.
Answer: Adsorption is accompanied by decrease of randomness. For the process to be spontaneous, G must be negative.
Hence, according to equation G =H-TS , G can be -ve only if H is negative.
Answer: Emulsions : An emulsion is a colloidal dispersion in which both the dispersed phase and dispersion medium are liquids.
Water in oil → Butter, cold creams.
(i) NaNO3 (ii) MgSO4 (iii) AlCl3
Answer:
AlCl3 (Aluminium chloride) is most effective in coagulating negatively charged hydrated ferric oxide sol.
Answer:
Homogeneous catalysis : When the reactants and the catalyst are in the same phase, the process is called homogeneous catalysis.
Example : 2SO2 (g)+O2 (g) 2SO3 (g)
Heterogeneous catalysis : When the reactants and the catalyst are in different phases, the process is called heterogeneous catalysis.
Example : 2SO2 (g) 2SO3 (g)
Answer: The process of setting colloidal particles is called coagulation or precipitation of the sol. Methods of coagulation :
Question 14. Explain the following terms giving one example for each :
(i) Micelles (ii) Aerosol
Answer: (i) Micelles : They are associated colloids showing colloidal behavior at high concentration and strong electrolytes at low concentration.
Example : soap, detergent.
(ii) Aerosol : Aerosol is a colloidal solution of solid or liquid (dispersed phase) in gas (dispersion medium).
Example : smoke, dust, fog, mist, cloud.
Question 15. What are lyophilic and lyophobic colloids? Which of these sols can be easily coagulated on the addition of small amounts of electrolytes?
Answer:
Lyophobic sols : Substances like metals, their sulfides, etc., when simply mixed with the dispersion medium do not form the colloidal sol. Their colloidal sols can only be prepared by specific methods. They are not very hydrated and are irreversible in nature. They are also called extrinsic colloids.
Example : As2S3 sol.
Lyophilic sols : Liquid loving colloids in which there is affinity between dispersed phase and dispersion medium.
Example : Starch sol, Gum sol, Gelatin sol
Question 16. What is the difference between oil/water (O/W) type and water/oil (W/O) type emulsions? Give an example of each type.
Answer: Difference between two types of emulsions are : Emulsions of oil in water in which oil is the dispersed phase and water is the dispersion medium.
Example : Milk is an emulsion of liquid fat dispersed in water.
Emulsions of water in oil in which water is the dispersed phase and oil is the dispersion medium. e.g. Cod liver oil is an emulsion of oil i.e. water is the dispersed phase and oil is the dispersion medium.
Two applications of emulsion are :
(1) The digestion of fats in the intestines takes place by the process of emulsification.
(2) Several oily drugs are prepared in the form of emulsion.
Question 17. What is the difference between multimolecular and macromolecular colloids? Give one example of each.
Answer: Multimolecular colloid is aggregation of a large number of atoms or smaller molecules of a substance having size in the colloidal range. Whereas macromolecular colloid is the solution containing macromolecules in the colloidal range.
Example: Multimolecular colloids: Gold sol,
Sulfur sol
Macromolecular colloids: Proteins,
Cellulose (any one)
Question 18. Write three distinct features of chemisorptions which are not found in physisorptions.
Answer: Three distinct features of chemisorptions :
(1) It is caused by chemical bond formation.
(2) It is highly specific in nature.
(3) It is irreversible.
Question 19. Explain the following terms :
(i) Peptization
(ii) Lyophobic colloids
(iii) Dialysis
Answer:
(i) Peptization : The conversion of freshly prepared ppt into colloidal solution by shaking with a dispersion medium containing a small amount of electrolyte.
(ii) Lyophobic colloids : Solvent hating colloids * are called lyophobic colloids. For example, Gold sol.
(iii) Dialysis : It is the process of removing a dissolved substance from a colloidal solution by means of diffusion through a membrane.
Question 20: Give reason why a finely divided substance is more effective as an adsorbent.
Answer : Adsorption is directly proportional to the surface area as adsorption is a surface phenomenon. A finely divided substance behaves like a good adsorbent because it has a large surface area. Both physisorption and chemisorption increase with an increase in the surface area.
Question 21: What are micelles? Give an example of a micellers system.
Answer : When soaps and detergents are dissolved in water, it forms micelle. The molecules of such substances contain a hydrophobic and a hydrophilic part. When they are present in the water, these substances arrange themselves in spherical structures in such a manner that their hydrophilic parts are pointing towards the outside, while the hydrophobic parts are present towards the center (as shown in the given figure). This is known as micelle formation.
Question 22: Give four uses of emulsions.
Answer : Uses of emulsions are:
(i) Formation of emulsions determine the cleansing action of the soap.
(ii) The process of emulsification is responsible for the digestion of fats in the intestines.
(iii) Emulsions are formed by adding antiseptics and disinfectants to water.
(iv) Emulsification is used to make medicines.
Question 23: Discuss the effect of pressure and temperature on the adsorption of gasses on solids.
Answer: Effect of pressure:
Adsorption increases with an increase in pressure, since adsorption is a reversible process and is accompanied by a decrease in pressure.
Effect of temperature:
In accordance with Le-Chatelier’s principle, the magnitude of adsorption decreases with an increase in temperature. Thus, adsorption is an exothermic process.
Question 24. Write the dispersed phase and dispersion medium of the following colloidal systems:
(i) Smoke
(ii) Milk
Answer:
(i) Smoke: Dispersed Phase → Solid;
Dispersed medium → Gas;
(ii) Milk: Dispersed Phase → Fat (Liquid);
Dispersed medium Liquid
Question 25. What is a ‘shape-selective catalyst’?
Answer: The catalyst reaction in which small sized molecules are absorbed in the pores and cavities of selective adsorbents like zeolites is known as shape-selective catalysis.
Answer: Difference between two types of emulsions are : Emulsions of oil in water in which oil is the dispersed phase and water is the dispersion medium.
Example : Milk is an emulsion of liquid fat dispersed in water.
Emulsions of water in oil in which water is the dispersed phase and oil is the dispersion medium. e.g. Cod liver oil is an emulsion of oil i.e. water is the dispersed phase and oil is the dispersion medium.
Two applications of emulsion are :
Answer: Three distinct features of chemisorptions :
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