CBSE 11th Standard Chemistry Subject Environmental Chemistry Ncert Exemplar 2 Mark Questions 2021
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CBSE 11th Standard Chemistry Subject Environmental Chemistry Ncert Exemplar 2 Mark Questions 2021
11th Standard CBSE
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Reg.No. :
Chemistry
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Dissolved oxygen in water is very important for aquatic life. What processes are responsible for the reduction of dissolved oxygen in water?
(a) -
What could be the harmful effects of improper management of industrial and domestic solid waste in a city?
(a) -
For dry cleaning in the place of tetrachloroethene, liquefied carbon dioxide with suitable detergent is an alternative solvent. What type of harm to the environment will be prevented by stopping use of tetrachloroethene? Will use of liquefied carbon dioxide with detergent be completely safe from the point of view of pollution. Explain.
(a) -
Ozone is a toxic gas and is a strong oxidising agent even then its presence in the stratosphere is very important. Explain what would happen if ozone from this region is completely removed?
(a) -
How is ozone produced in the stratosphere?
(a)
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CBSE 11th Standard Chemistry Subject Environmental Chemistry Ncert Exemplar 2 Mark Questions 2021 Answer Keys
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The processes which are responsible for the reduction of dissolved oxygen in water are excessive use of phosphatic and nitrate fertilisers, detergents, the discharge of human sewage and organic waste from food, paper and pulp industries. The microorganisms which oxidise organic matter also use oxygen dissolved in water. Moreover, during night, photosynthesis stops bu the aquatic plants continue to respire, resulting in reduction of dissolved oxygen.
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If domestic waste in a city is not properly managed, it may finds its way into sewers or may be eaten up by the cattle. The non-biodegradable waste like polythene bags, metal scrap etc., choke the sewers. The polythene bags if swallowed by the cattle can result into their death. Similarly, if industrial waste is not properly managed, it will cause pollution of the air, soil and water.
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(i) Tetrachloroethene, CI2C = CCI2 is suspected to be carcinogenic and also contaminates the ground water. This harmful effect will be prevented by using liquefied CO2 along with suitable detergent
(ii) Use of liquefied CO2 along with detergent will not be completely safe because most of the detergents are non-biodegradable and they cause water pollution. Moreover, liquefied CO2 will ultimately enter into the atmosphere and contribute to the green house effect. -
Ozone prevents harmful UV radiations of the Sun from reaching to the earth's surface, thereby it protects life from adverse effects of UV radiations. If ozone is removed completely from the stratosphere, the UV rays will reach to the earth and will lead to several diseases like sunburn, skin infection etc.
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Ozone in the stratosphere is a product of the action of UV radiations on dioxygen (O2 ) molecules. The UV radiations split apart molecular oxygen into free oxygen atoms. These oxygen atoms combine with the molecular oxygen to form ozone.
\(O_{ 2 }\left( g \right) \underrightarrow { UV \ radiations } \left( O \right) \left( g \right) +\left( O \right) \left( g \right) \)
\(O_{ 2 }\left( g \right) +\left( O \right) \left( g \right) \begin{matrix} UV \\ \rightleftharpoons \\ Radiations \end{matrix}O_{ 3 }\left( g \right) \)
