CBSE 12th Standard Chemistry Subject Value Based Questions 3 Mark Questions With Solution 2021
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CBSE 12th Standard Chemistry Subject Value Based Questions 3 Mark Questions With Solution 2021
12th Standard CBSE
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Reg.No. :
Chemistry
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Jagan went to Srinagar with his friend. He noticed that the taxi drivers always add ethylene glycol as a coolant in the radiator of the taxi and not water. He asked his driver, how much ethylene glycol he generally adds to the radiator. The taxi driver told him that he generally adds 30% ethylene glycol solution. On that day, the temperature of the valley was \(-10°C\) .
Answer the following questions:
(i) What is the role ethylene glycol when added to water?
(ii) Is the amount of ethylene glycol sufficient to avoid the freezing of water in car radiator when the temperature of the valley was \(-10°C\) ?(a) -
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?(a) -
Manoj went with his father to buy hinges for the door. The shopkeeper showed two types of hinges: normal iron hinges and the galvanized hinges. The normal hinges were costlier. Manoj's father opted for the cheaper normal iron hinges. Manoj suggested his father to buy galvanized hinges through these were costlier.
(a) what are the rationale for Manoj to buy galvanized hinges?
(b) What values are attached with this decision?(a) -
Sulphuric acid is manufactured by Contact process.During the process,the following reaction takes place:
\({ 2SO }_{ 2 }(g)+O_{ 2 }(g)\rightleftharpoons 2SO_{ 3 }(g)\)
This reaction is favoured by high pressure, However,the pressure is not increase beyond 3 bar.As a students of chemistry how will you justify this?(a) -
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?(a)
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CBSE 12th Standard Chemistry Subject Value Based Questions 3 Mark Questions With Solution 2021 Answer Keys
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(i) Ethylene glycol lowers the freezing point of water. It is called antifreeze solution.
(ii) 30% ethylene glycol solution means 30g of ethylene glycol in 100g of solution.
\({ \omega }_{ B }=30g,{ \omega }_{ A }=70g,{ K }_{ f }=1.86{ Km }^{ -1 },M_{ B }=62\)
\( { \triangle T }_{ f }=\frac { { K }_{ f }\times { \omega }_{ B }\times 1000 }{ { \omega }_{ A }\times { M }_{ B } } =\frac { 1.86\times 30\times 1000 }{ 70\times 62 } =12.86\)
The solution will freeze at\(-12.{ 86 }^{ \circ }C\) and therefore,it will be suitable. -
(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. -
(a) As a student of chemistry, we would prefer to buy the battery with cadmium plates, though it is costlier than the battery with lead plates. This is because
(i) Lead battery will result into harmful effects on human beings as well as on the environment because it causes environmental pollution.
(ii) A cadmium plated battery will have sustained long life benefit than short term gains with regard to health and money.
(b) Knowledge is useful only when put to practice; awareness of a lead-free petrol-legal aspect of pollution free environment. Less usage of lead batteries to keep ourselves and the environment healthy. -
Since the volume of the gaseous products is less than that of the gaseous reactants, high pressure should favour the oxidation of sulphur dioxide. But a very high pressure may cause the corrosion of the vessel in which oxidation is carried. Therefore, a pressure of 2 to 3 bar is sufficient for the oxidation.
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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.
