NCERT Class 11 Solutions Environmental Chemistry

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NCERT Class 11 Solutions Environmental Chemistry - NCERT Solutions prepared for CBSE students by the best teachers in Delhi.

Class XI Chapter 14 – Environmental Chemistry Chemistry

Question 14.1: Define environmental chemistry.

Answer Environmental chemistry is the study of chemical and biochemical processes occurring in nature. It deals with the study of origin, transport, reaction, effects, and fates of various chemical species in the environment.

Question 14.2: Explain tropospheric pollution in 100 words.

Answer Tropospheric pollution arises due to the presence of undesirable substances in the lowest layer of the atmosphere.

Oxides of sulphur, nitrogen, carbon, and hydrocarbons are the major gaseous pollutants. Oxides of sulphur (SO2 and SO3) and nitrogen (NO2, NO) are produced as a result ofburning of fossil fuels (coal, automobile fuel). These oxides react with water in the presence of atmospheric oxygen to form nitric acid (HNO3) and sulphuric acid (H2SO4), which leads to the formation of ‘Acid rain’. Acid rain causes harm to agriculture, plants, and trees. It also leads to various respiratory ailments. 

Hydrocarbons are carbon and hydrogen containing compounds that burn to produce oxides of carbon. Hydrocarbons are carcinogenic and their products are also major  pollutants. Carbon monoxide (CO) is poisonous in nature as it reacts with thehaemoglobin of blood, which can even result in death. Though carbon dioxide (CO2) is not toxic in nature, yet it contributes towards global warming by trapping the reflected IR rays. This results in the heating up of the Earth’s atmosphere, thereby leading to the melting of icebergs and glaciers.

Particulates of smoke, dust, mist, and fume are harmful for human health as they are likely to block the nasal passage of a person, causing respiratory ailments. Smoke and fog combine to produce smog during a cool, humid day, thereby reducing visibility to a large extent. Photochemical smog is formed due to the presence of PAN, ozone,

Class XI Chapter 14 – Environmental Chemistry Chemistry

Question 14.3: Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?

Answer Carbon dioxide (CO2) and carbon monoxide (CO) gases are emitted during the combustion of various fuels. Carbon monoxide is poisonous, whereas carbon-dioxide is non-toxic in nature. Carbon monoxide is poisonous because it is capable of forming a complex with haemoglobin (carboxyhaemoglobin), which is more stable than the oxygen-haemoglobin complex. The concentration range of 3–4% of carboxyhaemoglobin decreases the oxygen-carrying capacity of blood. This results in headaches, weak eyesight, nervousness, and cardiovascular disorders. A more increased concentration may even lead to death. Carbon dioxide is not poisonous. It proves harmful only at very high concentrations.

Question 14.4: List gases which are responsible for greenhouse effect.

Answer The major greenhouse gases are:

1) Carbon dioxide (CO2)

2) Methane (CH4)

3) Water (H2O)

4) Nitrous oxide (NO)

5) Ozone (O3)

6) Chlorofluorocarbons (CFCs)

Question 14.5: Statues and monuments in India are affected by acid rain. How?

Answer:Acid rain is a byproduct of various human activities that leads to the emission of oxides of sulphur and nitrogen in the atmosphere. These oxides undergo oxidation and then react with water vapour to form acids. Acid rain causes damage to buildings and structures made of stone and metal. In India, limestone is a major stone used in the construction of various monuments and statues, including the Taj Mahal. Acid rain reacts with limestone as: This results in the loss of lustre and colour of monuments, leading to their disfiguration.

Question 14.6: What is smog? How is classical smog different from photochemical smog?

Answer Smog is a kind of air pollution. It is the blend of smoke and fog. There are two kinds of smog:

a) Classical smog

b) Photochemical smog

Question 14.7: Write down the reactions involved during the formation of photochemical smog.

Answer Photochemical smog is formed as a result of the reaction of sunlight with hydrocarbons and nitrogen oxides. Ozone, nitric oxide, acrolein, formaldehyde, and peroxyacetyl nitrate (PAN) are common components of photochemical smog. The formation of photochemical smog can be summarized as follows: Burning of fossil fuels leads to the emission of hydrocarbons and nitrogen dioxide in the atmosphere. High concentrations of these pollutants in air results in their interaction with sunlight as follows:

While ozone is toxic in nature, both NO2 and O3 are oxidizing agents. They react with the unburnt hydrocarbons in air to produce formaldehyde, PAN, and acrolein.

Question 14.8: What are the harmful effects of photochemical smog and how can they be controlled?


Photochemical smog is oxidizing smog owing to the presence of NO2 and O3, causing corrosion of metals, stones, rubber, and painted surfaces. The other major components of photochemical smog are PAN, acrolein, and formaldehyde. Both PAN and ozone are eye irritants, while nitric oxide (formed from NO2) causes nose and throat irritation. At higher concentrations, photochemical smog causes chest pain, headaches, throat dryness, and various respiratory ailments.

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