Chemistry NCERT Exemplar Solutions Class 11th Chapter Fourteen

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The pollutants which get decomposed by bacteria like waste of vegetable and fruits, sewage, cow dung etc. are known as biodegradable pollutants. Non-biodegradable pollutants are those which do not get decomposed by bacteria e.g., mercury, polythene, aluminium, DDT etc. 

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This is observed that the improper disposal of wastes is one of the major causes of environmental pollution. Whenever domestic waste is not properly managed, it goes to the sewers and is eaten by cattle. Non-biodegradable wastes like metals, glass etc., choke the sewers or gut of the ruminants also many a times polythene bags are swallowed by cattle resulting in their deaths. Similarly, when industrial waste is not properly managed it leads to the air, water, and soil pollution.

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In the stratosphere, chlorofluorocarbons get broken down by powerful UV radiations, releasing chlorine free radical. This can be shown as-

This chlorine radical then reacts with stratospheric ozone to form chlorine monoxide radicals and molecular oxygen. The reaction involved is-

Reaction of chlorine monoxide radical with atomic oxygen produces more chlorine radicals and can be shown as-

This shows that chlorine radicals are continuously regenerated and cause the breakdown of ozone. Hence, CFCs are transporting

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The bacteria is held responsible for degrading biodegradable detergent feed on it and grows rapidly. While growing, they may use up all the oxygen dissolved in the water. The lack of oxygen kills all other forms of aquatic life such as fish and plants. Fertilizers contain phosphates as additives. The addition of phosphates in water further enhances algae growth. Such profuse growth of algae covers the water surface and reduces the oxygen concentration in water.

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Rainwater has a pH of 5.6 due to the presence of H+ ions formed by the reaction of rainwater with carbon dioxide present in the atmosphere. The reaction can be shown as-

H₂O (l)+CO₂ (g)→H₂CO₃ (aq)

H₂CO₃ (aq)→H+ (aq)+HCO₃⁻ (aq)

If the pH of the rainwater falls below 5.6 then it is known as acid rain. SO₂ and NO₂ after oxidation and reaction with water are major contributors to the acid rain.

2SO₂ (g )+ O₂ (g) + 2H₂O (l)→2H₂SO₄ (aq)

4NO₂ (g)+O₂ (g)+2H₂O (l)→4HNO₃⁻ (aq)

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Tetrachloroethene (Cl₂C=CCl₂ )was earlier used as solvent for dry cleaning. This compound contaminates the groundwater and is also suspected carcinogen. The process using this compound is now being replaced by a process where liquefied CO2 is used. Replacement of halogenated solvent by liquid carbon dioxide will result in less harm to the groundwater. These days, hydrogen peroxide is used for the purpose of bleaching clothes in the process of laundry, which gives better results and makes use of a lesser amount of water.

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Pesticides can be defined as the synthetic toxic chemicals  which are meant to kill pests. Most of the organic toxins are water insoluble and non- biodegradable in nature. These high persistent toxins are transferred from lower trophic level to the higher trophic level through the food chain. Over time, the concentration of toxins in higher animals reaches a level which merely causes serious metabolic and physiological disorders.