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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

Define environmental chemistry.

Shivani Sachdeva

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.
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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

Write down the reactions involved during the formation of photochemical smog.

Shivani Sachdeva

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... read more

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.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

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

Shivani Sachdeva

EFFECTS OF PHOTOCHEMICAL SMOG: 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... read more

EFFECTS OF PHOTOCHEMICAL SMOG:

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.

CONTROL MEASURES:

Photochemical smog results from the burring of fossil fuels and automobile fuels that emit NO2 and hydrocarbons, which in turn form ozone, PAN, and other chemicals. The use of catalytic converters in automobiles is recommended to prevent the release of NO2 and hydrocarbons into the atmosphere.

Plantation of plants such as Pinus, Juniparur, Quercus, Pyrus, and Vitis is also advised as these plants have the capability to metabolize NO2.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

What are the reactions involved for ozone layer depletion in the stratosphere?

Shivani Sachdeva

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.... read more

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)

The regeneration of causes a continuous breakdown of ozone present in the stratosphere, damaging the ozone layer.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

What do you mean by ozone hole? What are its consequences?

Shivani Sachdeva

In Polar regions, stratospheric clouds provide the surface for chlorine nitrate and hypochlorous acid, which react further to give molecular chlorine. Molecular chlorine and HOCl are photolysed to give chlorine-free radicals. The chlorine-free radicals lead to the decomposition of ozone as: Hence,... read more

In Polar regions, stratospheric clouds provide the surface for chlorine nitrate and hypochlorous acid, which react further to give molecular chlorine. Molecular chlorine and HOCl are photolysed to give chlorine-free radicals.

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’.

Effects of depletion of ozone layer

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.

Increase in UV radiations, decreases the moisture content of the soil and damages both plants and fibres.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

What are the major causes of water pollution? Explain.

Shivani Sachdeva

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... read more

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. Chemical pollutants: These are water soluble chemicals like heavy metals such as cadmium, mercury, nickel, etc. The presence of these chemicals (above the tolerance limit) can damage the kidneys, central nervous system, and liver.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

What would have happened if the greenhouse gases were totally missing in the earth’s atmosphere? Discuss.

Shivani Sachdeva

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,... read more

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.

In the absence of greenhouse gases, the average temperature of the Earth will decrease drastically, making it uninhabitable. As a result, life on Earth would be impossible.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

A large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping... read more
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. read less

Shivani Sachdeva

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... read more

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.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

How can domestic waste be used as manure?

Shivani Sachdeva

Depending upon the nature of the waste, domestic waste can be segregated into two categories i.e., biodegradable and non–biodegradable. Biodegradable waste such as leaves, rotten food, etc. should be deposited in land fills, where they get decomposed aerobically and anaerobically into manure. Non-biodegradable... read more

Depending upon the nature of the waste, domestic waste can be segregated into two categories i.e., biodegradable and non–biodegradable. Biodegradable waste such as leaves, rotten food, etc. should be deposited in land fills, where they get decomposed aerobically and anaerobically into manure. Non-biodegradable waste (which cannot be degraded) such as plastic, glass, metal scraps etc. should be sent for recycling.

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Answered on 10 Oct CBSE/Class 11/Science/Chemistry/Environmental Chemistry/NCERT Solutions/Exercise 14

For your agricultural field or garden you have developed a compost producing pit. Discuss the process... read more

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.

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Shivani Sachdeva

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... read more

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.

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