NCERT Solutions for Class 11 Chemistry Chapter 14
Environmental Chemistry Class 11
Chapter 14 Environmental Chemistry Exercise Solutions
Exercise : Solutions of Questions on Page Number : 413
Define environmental chemistry.
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 (SO2and SO3) and nitrogen (NO2, NO) 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 (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 the haemoglobin 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.
Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?
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.
List gases which are responsible for greenhouse effect.
The major greenhouse gases are:
1) Carbon dioxide (CO2)
2) Methane (CH4)
3) Water (H2O)
4) Nitrous oxide (NO)
5) Ozone (O3)
6)
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:
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 smogs can be differentiated as follows:
|
|
Classical smog |
Photochemical smog |
|
Occurrence |
It occurs in a cool, humid climate. |
It occurs in a dry, sunny climate. |
||
Components |
Smoke, fog, and sulphurdioxide. |
PAN, acrolein, ozone, formaldehyde, nitric oxide. |
||
Nature |
It is reducing in nature |
It is oxidizing in nature. |
||
|
|
|||
Write down the reactions involved during the formation of photochemical smog.
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:
While ozone is toxic in nature, both NO2and O3are oxidizing agents. They react with the unburnt hydrocarbons in air to produce formaldehyde, PAN, and acrolein.
What are the harmful effects of photochemical smog and how can they be controlled?
EFFECTS OF PHOTOCHEMICAL SMOG:
Photochemical smog is oxidizing smog owing to the presence of NO2and 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.
Photochemical smog results from the burring of fossil fuels and automobile fuelsthat emit NO2and hydrocarbons, which in turn form ozone, PAN, and other chemicals. The use of catalytic converters in automobiles is recommended to prevent the release of NO2and hydrocarbons into the atmosphere.
What are the reactions involved for ozone layer depletion in the stratosphere?
In the stratosphere, ozone is a product of the action of UV radiations on dioxygen as:
(i)
(ii)
Reaction (ii) indicates the dynamic equilibrium existing between the production and decomposition of ozone molecules. Any factor that disturbs the equilibrium may cause depletion of ozone layer by its decomposition. One such factor is the release of chlorofluorocarbon compounds (CFCs). These are non-reactive, non-flammable molecules that are used in refrigerators, air conditioners, plastics, and electronic industries.
Once released CFCs mix with atmospheric gases and reach the stratosphere, where they are decomposed by UV radiations.
(iii)
The chlorine free radical produced in reaction (iii) reacts with ozone as:
(iv)
The radicals further react with atomic oxygen to produce more chlorine radicals as: (v)
What do you mean by ozone hole? What are its consequences?
The chlorine-free radicals lead to the decomposition of ozone as:
Hence, a chain reaction is initiated. The chlorine-free radical is continuously regenerated, thereby depleting the ozone layer. This phenomenon is known as the as 'ozone hole'.
The ozone layer protects the Earth from the harmful UV radiations of the sun. With the depletion of the layer, more radiation will enter the Earth's atmosphere. UV radiations are harmful because they lead to the ageing of skin, cataract, skin cancer, and sunburns. They cause death of many phytoplanktons, which leads to a decrease of fish productivity. Excess exposure may even cause mutation in plants.
What are the major causes of water pollution? Explain.
Water pollution arises as a result of several human activities, which leads to the presence of several undesirable substances in water.
Major water pollutants with their sources have been tabulated as follows:
Pollutant |
Source |
Micro-organisms |
Domestic sewage |
Organic wastes |
Domestic sewage, decaying animals and plants, animal excreta and waste, discharge from food processing industries |
Plant nutrients |
Chemical fertilizers |
Toxic heavy metals |
Chemical factories and industries |
Sediments |
Strip mining and soil erosion |
Pesticides |
Chemicals used for killing fungi, weed, insects |
Radioactive substances |
Mining of uranium-containing minerals |
Heat |
Water used for cooling in industries |
Roles played by major pollutants are:
1. Pathogens: These water pollutants include bacteria and other organisms. They enter water from animal excreta and domestic sewage. Bacteria present in human excreta (for example, Escherichia coli and Streptococcus faecalis) cause gastrointestinal diseases.
2. Organic wastes: These are biodegradable wastes that pollute water as a result of run off. The presence of excess organic wastes in water decreases the amount of oxygen held by water. This decrease in the amount of dissolved oxygen inhibits aquatic life.
3.
Have you ever observed any water pollution in your area? What measures would you suggest to control it?
Water pollution arises as a result of various human activities. This includes discharges from wastewater treatment plants, run-off from agricultural fields, storm-water drainage, etc. Pollutants from these sources enter the water bodies, thereby contaminating the water and rendering it impure.
Industries and chemical factories discharge toxic, heavy metals such as Fe, Mn, Al, etc., along with organic wastes into water. Domestic sewage and animal excreta are also responsible for pathogenic contamination of water. These pollutants make water unfit for drinking.
What do you mean by Biochemical Oxygen Demand (BOD)?
Do you observe any soil pollution in your neighbourhood? What efforts will you make for controlling the soil pollution?
Major sources of soil pollution are industrial wastes and agricultural pollutants such as pesticides, fertilizers, etc.
It is very important to maintain the quality and fertility of soil to ensure and sustain the growth of plants and food crops.
Insecticides like DDT are not soluble in water. For this reason, they remain in soil for a long time, contaminating the root crops. Pesticides like Aldrin and Dieldrin are non-biodegradable and highly toxic in nature. They can enter the higher trophic levels through food chains, causing metabolic and physiological disorders. The same is true for industrial wastes that comprises of several toxic metals like Pb, As, Hg, Cd, etc.
Hence, the best way to check soil pollution is to avoid direct addition of pollutants to the soil. Also, wastes should undergo proper treatment. They should be recycled and only then, allowed to be dumped.
What are pesticides and herbicides? Explain giving examples.
Pesticides are a mixture of two or more substances. They are used for killing pests. Pests include insects, plant pathogens, weeds, mollusks, etc., that destroy the plant crop and spread diseases. Aldrin and dieldrin are the names of some common pesticides
What do you mean by green chemistry? How will it help decrease environmental pollution?
Green chemistry is a production process that aims at using the existing knowledge and principles of chemistry for developing and implementing chemical products and processes to reduce the use and generation of substances hazardous to the environment
What would have happened if the greenhouse gases were totally missing in the earth's atmosphere? Discuss.
Earth's most abundant greenhouse gases are CO2, CH4, O3, CFCs, and water vapour. These gases are present near the Earth's surface. They absorb solar energy that is radiated back from the surface of the Earth. The absorption of radiation results in the heating up of the atmosphere. Hence, greenhouse gases are essential for maintaining the temperature of the Earth for the sustenance of life.
A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping but you find an abundance of phytoplankton. Suggest a reason for the fish kill.
The amount of dissolved oxygen present in water is limited. The abundance of phytoplanktons causes depletion of this dissolved oxygen. This is because, phytoplanktons are degraded by bacteria present in water. For their decomposition, they require a large amount of oxygen. Hence, they consume the oxygen dissolved in water. As a result, the BOD level of water drops below 6 ppm, inhibiting the growth of fish and causing excessive fish-kill.
How can domestic waste be used as manure?
For your agricultural field or garden you have developed a compost producing pit. Discuss the process in the light of bad odour, flies and recycling of wastes for a good produce.
It is essential to take proper care of the compost producing pit in order to protect ourselves from bad odour and flies. It should be kept covered to minimize bad odour and prevent flies from entering it.
The recyclable waste should not be dumped in the compost producing pit. It should be sent to the industries through vendors for recycling.