CBSE 12th Standard Chemistry Subject Value Based Questions 3 Mark Questions 2021 Part - I
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CBSE 12th Standard Chemistry Subject Value Based Questions 3 Mark Questions 2021 Part - I
12th Standard CBSE
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Reg.No. :
Chemistry
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Rekha observed that her mother placed shrinked or dried vegetables in water before cutting these for cooking. After sometime, these vegetables looked fresh.
Answer the following questions:
(i) Why did Rekha's mother place the shrinked or dried vegetables in water?
(ii) What is the name of the process used and define it.
(iii) Would the temperature increase accelerate the process or not? -
Many food products are available in the market in tin cans. Jayant went to the market to buy tinned cans of a food product. The shopkeeper gave him a can which had scratches, though it had been recently packed. Jayant did not buy that can. How do you agree with Jayant's decision?
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In thermal power stations, coal is burnt to produce steam for generation of electricity The smoke produced is passed through electrostatic precipitators before allowing it to escape into the atmosphere
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Account for the following:
(i) Iron on reaction with HCI forms FeCl2 and not FeCI3.
(ii) Draw structure of XeO3. -
D.D.T is one of the most powerful insecticides which is effective against the mosquitoes that spread malaria. Mukesh's mother wanted to buy D.D.T from the market to use at night to protect her family from mosquitoes. But Mukesh stopped his mother from purchasing D.D.T.
(a) How did Mukesh convince her mother for not using D.D.T at night?
(b) What values are attached to suggestion of Mukesh?
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CBSE 12th Standard Chemistry Subject Value Based Questions 3 Mark Questions 2021 Part - I Answer Keys
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(i) The cell walls of the vegetables have semi-permeable membrane. When the vegetables have dried, the concentration of water inside becomes low. When the dried or shrinked vegetables are placed in water, water enters into the cells due to osmosis. Hence, they swell and return to the original form.
(ii) The process is osmosis. It is defined as the flow of the solvent molecules from the solvent to the solution or from less concentrated solution to a more concentrated solution through a semi-permeable membrane.
(iii) The process will be accelerated with increase of temperature because osmosis becomes faster with increase of temperature. -
Many food products are available in the markets in tin cans, which are made from steel with a very thin coating of tin. the thin layer, which is only a few thousands of a millimeter thick, prevents the steel from rusting. If the coating gets scratched, the can will soon corrode. This will allow bacteria from the air to cause food poisoning. Thus, the tin can with scratches have chances of getting spoiled. Hence, the decision of Jayant is justified.
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(i) To prevent the pJssage of particulates of smoke in the atmosphere.
(ii) Electrophoresis.
(iii) 'Coal contains impurities of sulfur, arsenic, lead etc. and therefore, the smoke will contaminate the air. These particles are injurious to health and have to be removed from the smoke.
(iv) The value promoted is a concern for keeping the environment clean and prevent air pollution. -
(i) Liberation of hydrogen prevents the formation of FeCI3.
(ii) Structure of XeO3
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(a) Though D.D.T is a very powerful insecticide for mosquitoes, yet the excessive use of D.D.T has many problems. The use of D.D.T has the following disadvantages:
(i) Many species of insects develop resistance to D.D.T.
(ii) It has a high toxicity towards fish.
(iii) The chemical stability of D.D.T and its fat solubility has problems.
(iv) It is not biodegradable and its residues accumulate in environment and its long term effects could be dangerous.
(v) D.D.T is not metabolized very rapidly by animals rather it gets deposited and stored in fatty tissues. Because of its dangerous effects, its use has been banned in U.S.A in 1973. However, in spite of its dangerous effects, D.D.T is still being used in India because of non-availability of other cheaper insecticides.
(b) Mukesh's suggestion is very important to protect our environment. Because of long-term dangerous side effects of D.D.T., it should not be used to save our environment.
