Chapter 14: Environmental Chemistry

Ans: Many techniques are used to control or reduce the formation of photochemical smog. 

(1) If we control the primary precursors of photochemical smog, such as nitrogen dioxide and hydrocarbons, the secondary precursors such as ozone and PAN of the photochemical smog will automatically get reduced.

(2) Mostly catalytic converters are used in automobiles to prevent the release of nitrogen oxide and hydrocarbons to the atmosphere. 

(3) Certain plants e.g., Pinus, Juniparus, Quercus, Pyrus and Vitis metabolise nitrogen oxide and hence their plantation could help in this.

Ans: The organic solvents like- benzene, carbon tetrachloride , toluene etc., are highly toxic in nature. Everyone needs to be careful while using them. For bleaching the cloth hydrogen peroxide is used which is not harmful. Earlier chlorine was used for bleaching the clothes.

Ans: The synthetic detergents are found to be non-biodegradable and hence their use in daily life is to be avoided. Good quality soaps need to be prepared from vegetable oil as they are biodegradable in nature.

Ans: In place of petrol and diesel, the use of CNG and LPG should be preferred as they are pollution free fuels. The other sources such as hydrogen, ethanol etc. can also be used in place of petrol and diesel.

Ans: \[\text{C}{{\text{O}}_{\text{2}}}\]gas is confined to the troposphere only and it forms nearly 0.03 per cent by volume of the atmosphere. With the increased use of fossil fuels, a large amount of carbon dioxide gets released into the atmosphere. Excess of carbon dioxide in the air is removed by the green plants and this maintains an appropriate level of it in the atmosphere. Green plants require carbon dioxide for the process of photosynthesis and  which in turn emits oxygen, thus maintaining the balance in nature. Deforestation and the burning of fossil fuels increase the level of carbon dioxide, and this disturbs the balance in the atmosphere. The increased amount of carbon dioxide in the air is mainly responsible for global warming. 

Ans: Since the earth’s surface is heated by the sunlight, it radiates a part of this energy back to the space as longer Infrared wavelengths and some of the heat gets trapped by CFCs and water vapours present in the atmosphere. They absorb IR radiations and block a large portion of earth’s emitted radiations. This radiation, absorbed, is partly remitted to the earth’s surface. Therefore, the earth’s surface gets heated up by the phenomenon called greenhouse effect.  Thus, the greenhouse effect is defined as the heating up of the earth’s surface due to trapping of infrared radiations reflected by the earth's surface by the carbon dioxide layer in the atmosphere. So, the heating up of the earth through the greenhouse effect is called global warming. 

Ans: 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. 

Ans: Tetrachloroethene \[\left( \text{C}{{\text{l}}_{\text{2}}}\text{C=CC}{{\text{l}}_{\text{2}}}\text{ } \right)\]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 \[\text{C}{{\text{O}}_{\text{2}}}\] 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.

Students who want to score well in Boards Exams or in competitive Examinations like NEET or JEE can boost their preparation by solving NCERT Exemplar. It gives them an extra edge over the other students. Several questions have been asked from the NCERT Exemplar both in Boards and competitive Examinations such as NEET or JEE. Many students solve the NCERT but they forget to do the NCERT Exemplar.  If we ask the toppers of any of the mentioned Examinations, most of them have solved the questions of NCERT Exemplars.

The secret to success in any Exam is question practice and there is no other better source for questions than NCERT exemplar. Students can get confused about which study materials to follow for their preparations. There is a lot of information on the internet. It is very easy for one’s preparation to get haphazard. 

In order to study a Chapter systematically, it is advised to read the Chapters from NCERT, solve their questions and then solve the NCERT exemplar for an extra edge. If you still have time, you can start by solving PYQs of the same. The key here is to practice and practice until you make your weak areas strong. Questions from reliable sources such as the NCERT Exemplar give the students a perfect idea of the type of questions that can be actually asked in the Exam. Students become more familiar with the important topics and the marking scheme.

If you solve questions from the NCERT Exemplar, you will be able to clear your concepts and be more confident about your preparations.

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