CBSE Class 12 Chemistry Surface Chemistry (3). CBSE issues sample papers every year for students for class 12 board exams. Students should solve the CBSE issued sample papers to understand the pattern of the question paper which will come in class 12 board exams this year. The sample papers have been provided with marking scheme. It’s always recommended to practice as many CBSE sample papers as possible before the board examinations. Sample papers should be always practiced in examination condition at home or school and the student should show the answers to teachers for checking or compare with the answers provided. Students can download the sample papers in pdf format free and score better marks in examinations. Refer to other links too for latest sample papers.
1.What are the physical states of dispersed phase and dispersion medium of froth?
2.What is the cause of Brownian movement among colloidal particles?
3.Arrange the solutions: True solution, colloidal solution, suspension in decreasing order of their particles size?
4.Give an example of micelles system?
5.Why is it necessary to remove CO when ammonia is obtained by Haber’s process?
6.How is adsorption of a gas related to its critical temperature?
7.What is meant by Shape Selective Catalyst?
8.Of the physiorption&chemisorptions, which type of adsorption has higher enthalpy of adsorption?
9.Write down the Example of Positive Sol?
10.Write down the Example of Negative Sol?
2 marks question.
1.(Q.) Define hardy-Schulze rule?
2.(Q.) Define flocculation value?
3.(Q.) What is the difference between a sol and a gel?
4.Q.) What are macromolecular and multimolecular colloids? How are they different from associated colloids?
5Q.)Give any two reasons for the origin of electrical charge on the colloidal particles.
6.(Q.) Differentiate between electrophoresis and electro-osmosis?
7.(Q.) Why lyophilic colloids are called reversible sols while lyophobic sols are called irreversible sols? Give on example of each.
8.(Q.) Explain cleansing action of soap.
9.(Q.) Differentiate between chemisorption and physisorption.
10.(Q.) Why is adsorption always exothermic?
Ans. 1 marks.
1.Ans - Dispersed phase is gas, dispersion medium is liquid.
2.Ans - Due to collision between particles
3.Ans – Suspension > colloidal > true solution
4.Ans – Sodium stearate (C17 H35 COO- Na+)
5.Ans- CO acts as poison catalyst for Haber’s process therefore it will lower the activity of solution therefore
it is necessary to remove when NH3 obtained by Haber’s process.
6.Ans- Higher the critical temperature of the gas. Greater is the ease of liquefaction.
i.e. greater Vander walls forces of attraction and hence large adsorption will occur
7.Ans – On the Shape Selective Catalyst, the rate depends upon pore size of the catalyst and the shape & size of the reactant and products molecules
8.Ans - chemisorptions.
9.Ans – Ferric hydro-oxide sol
10.Ans – Arsenic sulphide.
Ans. 2 marks
1.It is the capacity of an electrolyte to cause coagulation of a sol depends upon the number of charges on the ion having charge opposite to that possessed by the sol particles, but is independent of the charges on the ion having similar charge.
2.The number of milli moles of an electrolyte required to bring about the coagulation of one litre of a olloidal solution is called its flocculation value.
3.In a sol, dispersed medium is liquid and dispersed phase is solid. On the other hand, in a gel, dispersion medium is solid and dispersed phase is liquid.
4.Macromolecular colloids:-i)They are molecules of large size. ii) They have lyophobic property.
Multimolecular colloids:-i) They are formed by the aggregation of large number of atoms or molecules which
have diameter less than 1nm.ii) They have lyophilic property.Associated colloids:-i) they are formed by the
aggregation of large number of ions in concentrated solutionii) They contain both lyophilic and lyophobic groups
5.The two reasons are:
i) Due to electron capture by sol particles during electro dispersion of metals, due to preferential adsorption
of ions from solution
ii) Dissociation of colloidal sols.
6.Electrophoresis is the movement of colloidal particles under the influence of an electrical field.Electroosmosis s the movement of dispersion medium molecules under the influence of electric field when colloidal particles are not allowed to move
7.In the lyophilic colloids if the dispersed medium is separated from the dispersion medium the sol can beprepared again by simply remixing with the dispersion medium. So they are called reversible sols.
In lyophobic sols if small amount of electrolyte is added, the sols are readily precipitated and do not give
back the colloid by simple addition of the dispersion medium. So they are called irreversible sols. Example: metal sulphides.
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