Chemistry Class 11 NCERT Solutions: Chapter 14 Environmental Chemistry Part 1
Q: 1. Define environmental chemistry.
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.
Q: 2. Explain tropospheric pollution in 100 words.
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 and nitrogen are produced as a result Of burning of fossil fuels (coal, automobile fuel). These oxides react with water in the presence of atmospheric oxygen to form nitric acid and sulphuric acid 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 is poisonous in nature as it reacts with the haemoglobin of blood, which can even result in death. Though carbon dioxide 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, formaldehyde, and Acrolein. It causes eye irritation, headaches, and chest pain. It also leads to the cracking of rubber and does damage to plants.
Q: 3. Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?
Carbon dioxide and carbon monoxide 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 (carboxyhemoglobin), which is more stable than the oxygen-haemoglobin complex. The concentration range of of carboxyhemoglobin decreases the oxygen-carrying capacity of blood. This results in headaches, weak eyesight nervousness, and cardiovascular disorders. A more increased concentration may eve lead to death.
Carbon dioxide is not poisonous. It proves harmful only at very high concentrations.
Q: 4. List gases which are responsible for greenhouse effect.
The major greenhouse gases are:
(1) Carbon dioxide
(4) Nitrous oxide
Q: 5. Statues and monuments in India are affected by acid rain. How?
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.
Q: 6. What is smog? How is classical smog different from photochemical smog?
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
The two smog’s can be differentiated as follows:
It occurs in a cool, humid climate
It occurs in a dry, sunny climate
Smoke, fog, and sulphur dioxide
PAN, acrolein, ozone, formaldehyde, nitric oxide
It is reducing in nature
It is oxidizing in nature