Q1. Define environmental chemistry.
Ans. Environmental chemistry deals
with the study of the origin, transport,
reactions, effects and fates of
chemical species in the environment.
Q2. Explain tropospheric pollution.
Ans. Tropospheric pollution occurs due to the presence of undesirable
solid or gaseous particles in the air like oxides of sulphur, nitrogen,
carbon, hydrogen sulphide, hydrocarbons, ozone etc. Particulate
pollutants like dust, mist, fumes, smoke, smog etc. also cause
tropospheric pollution.
SO2: Oxides of sulphur are produced when fossil fuels containing
sulphur is burnt which is harmful to animals and plants.
N02: Dinitrogen and Dioxygen are the main constituents of air. At high
altitudes they combine to form oxides of nitrogen. Higher
concentrations of NO2 damages plants and retard the rate of
photosynthesis.
Hydrocarbons: These are composed of hydrogen and carbon only and
are formed by incomplete combustion of fuel used in automobiles.
They cause cancer.
Oxides of carbon:1. CO: Its one of the most serious air pollutants. It has the ability to
block the delivery of oxygen to the organs n tissues.
2. CO2: It is released by respiration, burning of fossil fuels for energy
and by decomposition of limestone. It causes global warming.
Q3. Carbon monoxide gas is more dangerous
than carbon dioxide. Why?
Ans. Carbon monoxide has the ability to
attach to the haemoglobin present in blood
300 times more than oxygen. Therefore it
stops the flow of oxygen to the organs and
tissues. Comparatively, carbon dioxide is
lesser reactive. Both oxides of carbon are
the main reasons for global warming.
Q4. List gases responsible for green house effect.
Ans. The gases are:1. Carbon dioxide
2. Methane
3. Ozone
4. CFCs
5. Water vapour
Q5. Statues and monuments of India are
affected by acid rain how?
Ans. The major acidic constituents of acid rain
are oxides of nitrogen and sulphur. Acid rain is
a major reason of spoiling of the monuments.
These oxides dissolve in water and make the
rain acidic. These rains react with the materials
used for the monuments and degrade them.
This causes the monuments to lose their colour
and texture and shape. It may even result in
the slow deformation of the monuments.
Q6. What is smog? How is classical smog different from
photochemical smog?
Ans. The word smog is derived from smoke and fog.
Smog= smoke + fog
CLASSICAL SMOG:
1.Classical smog occurs in cool and humid climate.
2.Major constituents of chemical smog are- smoke, fog and SO2
3.Chemically it is a reducing mixture and hence is called
REDUCING SMOG.
PHOTOCHEMICAL SMOG:
1.Photochemical smog occurs in warm, dry and sunny climate.
2.Major constituents are unsaturated hydrocarbons and nitrogen
oxides.
3.It has a high concentrations of oxidizing agents n hence is called
OXIDIZING SMOG.
Q7.Write down the reactions involved during
the formation of photochemical smog.
Ans.
1.NO2 absorbs energy from sunlight and
breaks up into nitric oxide and free oxygen
atom.
NO2 (g) ―hv―> NO (g) + O (g)
2.Oxygen atoms are very reactive and
combine with the O2 in air to produce ozone.
0(g) + O2(g) <―> O3
Q8. What are the harmful effects of photochemical smog? How can it
be controlled?
Ans. EFFECTS: Photochemical smog can have an effect on the
environment, on people’s health and even on various materials. The
main visible effect is the brown haze that can be seen above many
cities. The brown tinge is caused by very small liquid and solid particles
scattering the light. Chemicals such as nitrogen oxides, ozone and
peroxyacetyl nitrate (PAN) can have harmful effects on plants. These
substances can reduce or even stop growth in plants by reducing
photosynthesis. Ozone, even in small quantities, can achieve this, but
PAN is even more toxic to plants than ozone. Nitrogen oxides can
contribute to problems with heart and lungs, eye irritation and
respiratory problems.
PRECAUTIONS:
The main method of lowering the levels of nitrogen oxides is by a
process called ‘catalytic reduction’, which is used in industry and in
motor vehicle. Using less air in combustion can reduce emissions of
nitrogen oxides. Temperature also has an effect on emissions—the
lower the temperature of combustion, the lower the production of
nitrogen oxides
Q9. What are the reactions involved for the ozone layer depletion in
the stratosphere?
Ans. A set of unique conditions are responsible for an ozone hole.
1. In summer season, nitrogen dioxide and methane react wit chlorine
monoxide
ClO• (g) + NO2  ClONO2 (g)
2. And chlorine atoms forming chlorine sinks, preventing much ozone
depletion.
Cl• (g) + CH4  •CH3 (g) + HCl (g)
3. These polar stratospheric clouds provide surface on which chlorine
nitrate is formed gets hydrolyzed to form hypochlorous acid.
ClONO2 (g) + H20 (g)  HOCl (g) + HNO3 (g)
ClONO2 (g) + HCl (g)  Cl2 (g) + HNO3 (g)
4. The sun’s warmth breaks up the clouds and HOCl and Cl2 are
photolyzed by sunlight.
HOCl (g)  •OH (g) + Cl (g)
Cl2 (g)  2•Cl (g)
Q10. What do you mean by ozone hole? What are its
consequences?
Ans. In 1980s atmospheric scientists working in Antarctica
reported about depletion of ozone layer commonly known as
OZONE HOLE. With the depletion of the ozone layer, more
UV radiation filters into troposphere. UV radiations lead to
ageing of skin, cataract, sunburns, skin cancer, killing of many
phytoplankton, damage to fish productivity etc. It has also
been reported that plant proteins get easily affected by UV
radiations which leads to the harmful mutation of cells. It also
increases evaporation of surface water through the stomata
of the leaves and decreases the moisture content of the soil.
Increase in UV radiations damage paints and fibers, causing
then to fade faster.
Q11. What are the major reasons for water
pollutions?
Ans. Pollution of water originates from human
activities. Through different paths, pollution
reaches surface or ground water. Easily
identified source or place of pollution is called as
point source. Major water pollutants areMicro-organisms, organic wastes, plant nutrients,
toxic heavy metals, sediments, pesticides,
radioactive substances etc.
Q12. What do you mean by Biochemical Oxygen
Demand (BOD)?
Ans. The amount of oxygen required by bacteria to
break down the organic matter present in a certain
volume of a sample of water is called Biochemical
Oxygen Demand (BOD). The amount of BOD in the
water is a measure of the amount of organic
material in the water, in terms of how much oxygen
will be required to break it down biologically. Clean
water would have BOD value less than 5ppm
whereas highly polluted water could have a BOD
value of 17ppm or more.
Q13. What are pesticides and herbicides? Explain with
example.
Ans. Pesticides are basically synthetic toxic chemical
with ecological repercussions. The repeated use of the
same or similar pesticides give rise to pests that are
resistant to that group of pesticides thus making them
ineffective. Some common examples are- DDT, Aldrin,
and Dieldrin.
Herbicides are toxic to mammals but not as
much as organo-chlorides. These decompose in a few
months. Some cause birth effects. Some common
examples are- sodium chlorate (NaClO3) and sodium
arsinite (Na3AsO3).
Q14. What do you mean by green chemistry? How will it help
decrease environmental pollution?
Ans. Green chemistry is a way of thinking and is about
utilizing the existing knowledge and principles of chemistry
and other sciences to reduce the adverse impact on
environment. Green chemistry is a production process that
would bring about minimum pollution or deterioration to the
environment. The byproducts generated during a process, if
not usually gainfully, add to the environmental pollution. Such
processes are not only environmental unfriendly but also costineffective. The waste generation and its disposal both are
economically unsound. Utilization of existing knowledgebase
for reducing the chemical hazards along with the
developmental activities is the foundation of green chemistry.
Q15. What would happen if the greenhouse gases
were totally missing in the earth’s atmosphere?
Ans. Just like plants are grown in greenhouses in
cold areas, our earth is surrounded by a thin
blanket which keeps it warm. It is called the natural
greenhouse effect. It helps maintain the
temperature perfect for sustaining life. It partly
absorbs and reflects the radiation’s from the sun.
It helps to maintain the temperature of earth.
Without these gases, the UV radiations could easily
enter the earth and the temperature on earth
would have been very high and inappropriate to
sustain life.
Q16. A large number of fish are suddenly found
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.
Ans. If there is no evidence of toxic dumping, then
the only possible reason for the fish kill must be
chemical pollutants. Bacteria which feed on
biodegradable detergents rapidly feed on the oxygen
present in the water. This lack of oxygen kills the
organisms of the water body. This is called
eutrophication. The presence of such bacteria must
have resulted in the fish kill.
Q17. How can domestic wastes be used as
manure?
Ans. Domestic wastes are collected in small bins
which are then transferred to community bins
by private or municipal workers. The waste if
not collected in garbage bins, finds its way into
sewers. Some of it is eaten by cattle. Nonbiodegradable wastes like polythene bag, metal
scraps, etc. choke the sewers and result in
several harmful diseases. By using methods like
composting, bio-gas plants we can easily convert
the problem causing waste into useful manure or
source of energy.
Q18. Give examples of green chemistry in day-to-day life.
Ans. Green chemistry has many uses in day-to-day life.
Dry cleaning: the compound used earlier for dry cleaning
(CCl2=CCl2) used to contaminate the ground water. Now
liquefied carbon dioxide is used instead which lessens the
contamination of the ground water.
Bleaching of paper: chlorine gas was used earlier for
bleaching paper. These days, hydrogen peroxide (H2O2) with
suitable catalyst, which promotes the bleaching action of
hydrogen peroxide, is used.
synthesis of chemicals: ethanol (CH3CHO) is now
commercially prepared by one step oxidation of ethene in
the presence of ionic catalyst in aqueous medium with an
yield of 90%.
CH2=CH2 + O2 CH3CHO (90%)