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(Chapter – 14) (Environmental Chemistry)
(Class – XI)
Question 14
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Answer 14
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It deals with the study of origin, transport, reaction, effects, and fates of various
chemical species in the environment
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2:
Explain tropospheric pollution in 100 words
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2:
Tropospheric pollution arises due to the presence of undesirable substances in the lowest
layer of the atmosphere
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Oxides of sulphur (SO2 and SO3) and nitrogen (NO2, NO) are produced as a result of
burning of fossil fuels (coal, automobile fuel)
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Acid rain causes harm to agriculture, plants, and trees
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Hydrocarbons are carbon and hydrogen containing compounds that burn to produce oxides
of carbon
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Carbon monoxide (CO) is poisonous in nature as it reacts with the haemoglobin of blood,
which can even result in death
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This results in the
heating up of the Earth’s atmosphere, thereby leading to the melting of icebergs and
glaciers
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Smoke and fog
combine to produce smog during a cool, humid day, thereby reducing visibility to a large

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extent
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It causes eye irritation, headaches, and chest pain
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Question 14
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Why?
Answer 14
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Carbon monoxide is poisonous, whereas carbon-dioxide is non-toxic in
nature
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The concentration range of 3–4% of carboxyhaemoglobin decreases the oxygencarrying capacity of blood
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A more increased concentration may even lead to death
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It proves harmful only at very high concentrations
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4:
List gases which are responsible for greenhouse effect
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4:
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)

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Question 14
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How?
Answer 14
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These oxides undergo oxidation and then react
with water vapour to form acids
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In India,
limestone is a major stone used in the construction of various monuments and statues,
including the Taj Mahal
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Question 14
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6:
Smog is a kind of air pollution
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There are two kinds of
smog:
a) Classical smog
b) Photochemical smog
The two smogs can be differentiated as follows:

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Classical smog

Photochemical smog

Occurrence

It occurs in a cool, humid
climate
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Components

Smoke, fog and
ulphurdioxide
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Nature

It is reducing in nature

It is oxidizing in nature
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7:
Write down the reactions involved during the formation of photochemical smog
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7:
Photochemical smog is formed as a result of the reaction of sunlight with hydrocarbons
and nitrogen oxides
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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
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They react with the
unburnt hydrocarbons in air to produce formaldehyde, PAN, and acrolein
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8:
What are the harmful effects of photochemical smog and how can they be controlled?
Answer 14
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The other major components of
photochemical smog are PAN, acrolein, and formaldehyde
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At higher
concentrations, photochemical smog causes chest pain, headaches, throat dryness, and
various respiratory ailments
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The use of
catalytic converters in automobiles is recommended to prevent the release of NO 2 and
hydrocarbons into the atmosphere
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Question 14
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9:
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
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One such factor is the release of
chlorofluorocarbon compounds (CFCs)
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Once released CFCs mix with atmospheric gases and reach the stratosphere, where they
are decomposed by UV radiations
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Question 14
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10:
In Polar regions, stratospheric clouds provide the surface for chlorine nitrate and
hypochlorous acid, which react further to give molecular chlorine
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The chlorine-free radicals lead to the decomposition of ozone as:

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Hence, a chain reaction is initiated
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This phenomenon is known as the as ‘ozone hole’
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With the
depletion of the layer, more radiation will enter the Earth’s atmosphere
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They
cause death of many phytoplanktons, which leads to a decrease of fish productivity
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Increase in UV radiations, decreases the moisture content of the soil and damages both
plants and fibres
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11:
What are the major causes of water pollution? Explain
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11:
Water pollution arises as a result of several human activities, which leads to the presence
of several undesirable substances in water
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Pathogens: These water pollutants include bacteria and other organisms
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Bacteria present in human excreta
(for example, Escherichia coli and Streptococcus faecalis) cause gastrointestinal diseases
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Organic wastes: These are biodegradable wastes that pollute water as a result of

run off
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This decrease in the amount of dissolved oxygen inhibits aquatic life
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Chemical pollutants: These are water soluble chemicals like heavy metals such

as cadmium, mercury, nickel, etc
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Question 14
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12:
Water pollution arises as a result of various human activities
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Pollutants from these sources enter the water bodies, thereby contaminating the water
and rendering it impure
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,
along with organic wastes into water
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These pollutants make water unfit for
drinking
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The concentration of these pollutants should
be checked regularly
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Question 14
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13:
Biochemical oxygen demand is the amount of oxygen required by bacteria to decompose
organic matter in a certain volume of sample of water
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Question 14
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14:
Major sources of soil pollution are industrial wastes and agricultural pollutants such as
pesticides, fertilizers, etc
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Insecticides like DDT are not soluble in water
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Pesticides like Aldrin and Dieldrin are nonbiodegradable and highly toxic in nature
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The same is true for industrial
wastes that comprises of several toxic metals like Pb, As, Hg, Cd, etc
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Also, wastes should undergo proper treatment
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Question 14
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Answer 14
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They are used for killing pests
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, that destroy the plant crop and
spread diseases
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For example, sodium chlorate
(NAClO3), sodium arsenite (Na3AsO3), etc
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16:
What do you mean by green chemistry? How will it help decrease environmental pollution?
Answer 14
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The release
of different harmful chemicals (particulates, gases, organic and inorganic wastes) causes
environmental pollution
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This prevents
or limits chemical pollutants from being introduced into the environment
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Question 14
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Answer 14
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These
gases are present near the Earth’s surface
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The absorption of radiation results in the heating up of the
atmosphere
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In the absence of greenhouse gases, the average temperature of the Earth will decrease
drastically, making it uninhabitable
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Question 14
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There is no evidence of
toxic dumping but you find an abundance of phytoplankton
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Answer 14
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The abundance of
phytoplanktons causes depletion of this dissolved oxygen
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For their decomposition, they require a large
amount of oxygen
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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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19:
How can domestic waste be used as manure?
Answer 14
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e
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Biodegradable waste such as
leaves, rotten food, etc
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Non-biodegradable waste (which cannot be
degraded) such as plastic, glass, metal scraps etc
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Question 14
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Discuss
the process in the light of bad odour, flies and recycling of wastes for a good produce
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20:
It is essential to take proper care of the compost producing pit in order to protect ourselves
from bad odour and flies
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The
recyclable waste should not be dumped in the compost producing pit
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