CBSE Class 12 Chemistry Surface Chemistry (2). 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.Bleeding caused by a nick from a razor during shaving can be stopped by rubbing with alum. Why?
Ans: Blood is a negatively charged colloidal solution. When alum is rubbed the positively charged Al3+ ions from alum neutralizes the charge on the particles and makes it coagulate to form a clot.
2. In which of the following does adsorption take place and why?
(i) Silica gets placed in the atmosphere saturated with water.
(ii) Anhydrous CaCl2 placed in the atmosphere saturated with water.
Ans: Water vapour gets adsorbed on the surface of silica since it is a good adsorbent.
3. Action of soap is due to emulsification and micelle formation. Comment.
Ans: Soap molecules adsorb on to the dirt surface and try to emulsify it by forming micelles. Soap micelles thus make the insoluble dirt(greasy materials) into colloidal form such that it gets washed away by water.
4. What is the use of ZSM-5?
Ans: It converts alcohols directly into gasoline (petrol) by dehydrating them to give a mixture of hydrocarbons.
5. Give one example for each (i) sol (ii) gel.
Ans: (i) paints (ii)Butter or any other correct options.
6. What is collodion?
Ans: It is a 4% solution of nitrocellulose in a mixture of alcohol and ether.
7. Can we form a colloid with two gaseous components?Comment.
Ans: No. a gas mixed with another gas forms a homogeneous mixture which does not come under a colloidal system.
8. What are the physical states of the dispersion medium and dispersed phase in froth?
Ans: In froth, the dispersed phase is a gas while dispersion medium is a liquid.
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