CBSE 12th Standard Chemistry Subject Solution Value Based Questions 3 Mark Questions With Solution 2021
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CBSE 12th Standard Chemistry Subject Solution Value Based Questions 3 Mark Questions With Solution 2021
12th Standard CBSE
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Reg.No. :
Chemistry
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Deep sea divers have been using the compressed air containing \({ N }_{ 2 }\) in addition to \({ O }_{ 2 }\) for breathing. When the sea diver breathes in compressed air at a depth, more \({ N }_{ 2 }\) dissolves in the blood and other body fluids than would dissolve at the surface because the pressure at the depth is far greater than surface atmospheric pressure. When the diver comes towards the surface, the pressure decreases and \({ N }_{ 2 }\) comes out of the body quickly forming bubbles in the blood stream which restrict blood flow and affect the transmission of nerve impulses. This results into a condition called 'the bends' which is dangerous and painful. To avoid this condition, professionals now use air diluted with helium. As a student of chemistry, can you analyse as to why helium is used?
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Common salt \((NaCI)\) and calcium chloride \((CaCI_{ 2 })\) are used to clear snow on the roads. The cost of sodium chloride and calcium chloride is almost the same. As a student of chemistry which salt would you prefer to purchase and why?
(a) -
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)
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CBSE 12th Standard Chemistry Subject Solution Value Based Questions 3 Mark Questions With Solution 2021 Answer Keys
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To avoid the condition of bends, as a precautionary step, most professional divers today use a helium-oxygen mixture instead of a nitrogen-oxygen mixture in the compressed gas tanks. This is mainly because of lower solubility of helium in the blood than nitrogen. Moreover, because of small size of He atoms as compared to nitrogen molecules these pass through cell walls without damaging them. The excess 02 dissolved in the blood is used in metabolism and does not cause the condition of bends.
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Sodium chloride \((NaCI)\) is preferred over calcium chloride \(({ CaCI }_{ 2 })\).This is because less amount of sodium chloride is needed in order to bring about same depression in freezing point. For example, if it is desired to decrease the freezing point by 10°C,the amount of NaCI d CaCl2 needed to be dissolved in
1 kg of water can be calculated from the formula:
\(\triangle { T }_{ f }=\frac { { iK }_{ f }\times { W }_{ B }\times 1000 }{ { W }_{ A }\times M_{ B } }\)
\(ForNaCI,\quad NaCI\rightleftharpoons { Na }^{ + }{ CI }^{ - }\quad i=2\)
\(\triangle { T }_{ f }={ 10 }^{ \circ },{ W }_{ A }=1000g,{ K }_{ f }=1.86 \ K{ m }^{ -1 },{ W }_{ B }=?,\)
\( { M }_{ B }=58.5\)
\( 10=\frac { 2\times1.86\times{ W }_{ B }\times1000 }{ 1000\times58.5 } \)
\( or \ \ \ \ { W }_{ B }=\frac { 10X1000X58.5 }{ 2X1.86X1000 } =157.26g\)
\( For \ { CaCI }_{ 2 },{ CaCI }_{ 2 }\rightleftharpoons { Ca }^{ 2+ }+2{ CI }^{ - } \ i=3\)
\( \triangle { T }_{ f }={ 10 }^{ \circ },{ W }_{ A }=1000g,{ K }_{ f }=1.86 \ K{ m }^{ -1 },{ W }_{ B }=?{ M }_{ B }=111\)
\(10=\frac { 3\times1.86\times{ W }_{ B }\times1000 }{ 1000\times111 } \)
\( or \ { W }_{ B }=\frac { 10\times1000\times111 }{ 3\times1.86\times1000 } =198.92g\)
Therefore, less amount of NaCI is needed and it should be preferred. -
(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.
