Coupon Accepted Successfully!



Define environmental chemistry.

The study of the origin, transport, reactions, effects and fates of chemical species that occur in nature and those produced as a result of certain human activities is called environmental chemistry.


Explain tropospheric pollution in 100 words.

Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air. 
Particulate pollutants: These are dust, mist, fumes, smoke, smog etc.

Gaseous air pollutants: These are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.


Carbon monoxide gas is more dangerous than carbon dioxide gas. Why?

Carbon monoxide gas is more dangerous than carbon dioxide gas because Carbon monoxide reacts with haemoglobin to form carboxy- haemoglobin which affects the capacity of haemoglobins to oxygen transport.


List gases which are responsible for green house effect.

The gases that are responsible for green house effect are carbon dioxide, methane, water vapours, nitrous oxide, CFCs and ozone.


Statues and monuments in India are affected by acid rain. How?

Statues and monuments made up of marble and limestone (CaCO3) are slowly corroded as the rain water containing the acids fall on them. Actually, both sulphuric acid and nitric acid dissolve calcium carbonate to form calcium sulphate and calcium nitrate respectively.

CaCO3 + H2SO4 CaSO4 + CO2 + H2O

CaCO3 + 2HNO3 Ca(NO3)2 + CO2 + H2

Since this salts are water soluble, they are slowly washed away resulting in slow corrosion of these monuments and statues.


What is smog? How is classical smog different from photochemical smogs?

Smog is a combination of 'smoke' and 'fog'. This is because it is formed for the first time due to the condensation of some kind of fog on the carbon particles present in the smoke produced due to combustion of domestic fuels and industrial fuels like coal and petroleum.

Difference between classical smog and photo chemical smog:

Classical Smog

Photochemical Smog

1. This type of smog was first observed in London in 1952.

1. This type of smog was observed in Los Angeles in 1950.

2. It involves smoke and fog. 2. It does not involves any smoke or fog. The word smog is misnomer here.
3. This type of smog is formed due to the presence of SO2 and humidity in the air which combines to from H2SO4 fog which deposits on the particles. 3. It is formed due to the photochemical reactions taking place when air combines with NO2 and hydrocarbons.
4. It is formed in the month of winter particularly in the morning hour when the temperature is low. 4. It is formed in the month of summer during afternoon when there is bright sunlight so that photochemical reactions can take place.
5. It causes bronchitis, irritations; problems in the lungs. 5. It causes irritation in the eyes.
6. It is reducing in character. 6. It is oxidizing in character.


Write down the reactions involved during the formation of photochemical smog

Photochemical smog is produced from the action of sunlight on the nitrogen oxides and hydrocarbons present in the exhaust gases of the automobiles and factories. The NO is oxidized by the atmospheric oxygen of NO2

         High temperature
N2 + O2 2NO

2NO + O2 2NO2

NO2 then undergoes photochemical decomposition in the presence of sun light.

NO2 (g) NO (g) + O(g)

The free oxygen atom so formed reacts with atmospheric oxygen to form ozone.

O2 (g) + O(g) O3(g)

Ozone then reacts rapidly with NO (g) to form NO2(g)

NO(g) + O2(g) NO2(g) + O2(g)

Fog + Smoke / dust + PAN Photochemical smog.


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

The harmful effects of photochemical smog are: 
i) It decreases the visibility and thus affects the air and road traffic.

ii) It damages plants .

iii) Rubber on exposure to photochemical smog loses it elasticity and becomes inflexible and brittle.

iv) Photochemical smog causes eye irritation. 

Control of Photochemical smog:
The best way to reduce the formation of photo chemical smog is to prevent the release of nitrogen oxides and unburnt bydrocarbons into the atmosphere. Thus the simplest way to control photo- chemical smog is to

i) Minimise the use of personal vehicles

ii) Install efficient catalytic converters in automobiles. Photochemical smogs can also be suppressed by using certain compounds that generate free radicals. These free radicals readily combine with the free radical precursors of the photochemical smog.


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

The reactions which deplete ozone layer in the stratosphere are
CF2Cl2(g) + hv
Cl-(g) + CF2Cl-(g)
Cl(g) + O3 (g) ClO-(g) + O2(g)
ClO.(g) + O(g)
.Cl(g) + O2(g)
The active .Cl(g) radicals are once again available for reacting with more ozone.


What do you mean by ozone hole? What are its consequences?
The ozone layer of lowered ozone concentration over Antartica is called ozone hole. This loss occurred due to depletion of ozone in the ozone layer.

The consequences of ozone layer depletion are
i) It affects plants, chlorophyll, proteins and causes harmful mutation in them.

ii) It will upset the heat balance of the earth.

iii) It would cause ecological balances, which would adversely affect man and animals.

iv) Ultraviolet radiation coming from the sun can pass through stratosphere and reach on the earth, causing cancer. Skin cancer chances are more.


What are the major causes of water pollution? Explain.

Water pollution can be caused in a number of ways:

These are the chemical substances which are added to the soil to provide the essential minerals containing N.P.S etc. the common fertilizers are calcium ammonium nitrate, urea, triple superphosphate, potassium sulphate, potassium nitrate etc. however, a certain part of these fertilizers reacts with water chemically (known as leaching) and pollutes the underground water. When this water is used for drinking purposes containing potassium nitrate in particular, it harms the respiratory system.

These include insecticides, fungicides, herbicides, rodenticides, etc. these are mostly chemically chlorinated hydrocarbons, organophosphates, metallic salts etc. pesticides dissolve in water to small extent and pollute it. Since all the pesticides are toxic in nature, they are injurious to both plants and animals. The frequent use of pesticides without proper control can lead to deformities in foetus, nervous system, stomach cancer, darkened skin and can also cause damage to eyes.

Organic Pollutants
It includes manures, wastes from food processing, rags, paper discards, decaying plants etc. and other organic wastes. All of them cause pollution of water. They are decomposed by aerobic bacteria into carbon dioxide, nitrates, sulphates, phosphates etc. but they take up dissolved oxygen from water. As a result, the oxygen content in water decrease considerably. This causes the death of aquatic animals particularly the fish.

Industrial wastes
The compounds of lead, mercury, cadmium, nickel, cobalt, zinc erc. Which are the products of chemical reactions carried in the industrial units also pollute water to a large extent and are responsible for many diseases.


Have you ever observed any water pollution in your area? What measures would you suggest to control it?

Yes, I have observed polluted water flowing in open sewage drains in my area.

We can control if it by the following measures:
a. Sewage must be churned by machines so that the large pieces may break into smaller ones and may get mixed thoroughly. The churned sewage is passed into a tank with a gentle slope. Heavier particles settle and the water flowing down in relatively pure.

b. Water must be sterilized with the help of chlorination. It kills microbes of sewage fungus as well as some pathogens, spores or cytes. Chlorination is very essential particular in rainy seasons.

c. Treatment of water with alum, lime etc., also helps in its purification.


What do you mean by Biochemical Oxygen Demand (BOD)?

BOD is Biochemical Oxygen Demand. It is a measure of dissolved oxygen that would be needed by micro-organisms to oxidize some of the inorganic and organic compounds present in the polluted water.


Do you observe any soil pollution in your neighbourhood? What efforts will you make for controlling the soil pollution?

We have observed soil pollution in nearby agricultural fields. This is due to the use of lot of fertilizers. Fertilizers are chemical substances which helps the soil to become fertile. But excess of fertilizer pass to the ground water from the soil and as run off to lakes rivers and seas, and are harmful to aquatic animals.

The Control of soil pollution can be made by using manure and bio fertilizers instead of fertilizers:

Use of manure
Manure is a semi- decayed organic matter which is added to the solid to maintain fertility. These are mostly prepared from animal dung and other farm refuse. These are much better than the commonly used fertilizers.

Use of biofertilizers
These organisms are inoculated in water to bring about nutrient enrichment of the solid, e.g., nitrogen fixing bacteria and blue- green algae


What are pesticides and herbicides? Explain giving examples.

Ans. Pesticides
Pesticides are basically synthetic toxic chemicals .They are used to kill or block the reproductive processes of unwanted organisms. The repeated use of the some of similar pesticides gives rise to pests that are resistant to that group of pesticides thus making the pesticides ineffective. Examples are DDT, Aldrin, Dieldrin etc.

Herbicides are used to kill weeds. Sodium chlorate, NaClO3 and sodium arsenite Na3AsO3 were commonly used as weed killers in the first half of the last century, but inorganic arsenic compounds, inorganic arsenic compounds, in particular are toxic to mammals, organic herbicides are, therefore, now used. They are much more toxic to certain types of plants than to others. Organic herbicides such as triazines are presently widely used to kill weeds in corn fields.


What do you mean by green chemistry? How will it help decrease environmental pollution?

Green chemistry simply utilizes the information that is now available to the scientific community about the toxicity and other hazards posed by certain chemicals in order to fully evaluate the negative as well as positive impact of the chemistry being designed. Database of information on the hazardous properties of chemicals have only recently become available. In the previous years the absence of these data meant that chemists could not effectively evaluate the consequences of the chemical substances that were being designed and synthesized. Since this is no longer the case, it is the responsibility of the chemists and chemical community to use this information.

It will help decrease environmental pollution because of the following processes:

Switch over to alternative fuels for an automobile reduces the pollution. Examples – uses of CNG in Delhi has greatly reduced the pollution in the city.

Use of CO2 as blowing agent for the manufacture of polystyerene foam sheet packaging material has eliminated the usage of CFCs which cause ozone depletion.

Designing of safer marine antifouling compound ‘Sea-nine’ that degrades far more rapidly than organotins which persist in the marine development and cause pollution problems.

Development of a new method to produce ibuprofen with 99% yield, avoiding the usage of large quantity of solvents and wastes associated with the traditional methods.


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

The green house gas carbon dioxide takes part in the photosynthesis process carried out by green plants to prepare food for plants and animals. In the absence of CO2, it will be not possible for green plants to prepare food.

The green house gas, carbon dioxide produces green house effect, leading to the heating of earth and its atmosphere, which is essential for our survival. In the absence of green house gases, heating of earth and its atmosphere will not be possible.


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.

Eutrophication causes a large number of fishes found floating dead of a lake. The presence of phosphate anion encourages the formation of algae, which in turn reduces the concentration of dissolved oxygen in water. This process of depletion of concentration of oxygen in water is called eutrophication.


How can domestic waste be used as manure?

The domestic waste can be used as manure by digging a pit and domestic wastes are put in this pit. A layer of soil is used to cover them. The decomposition is facilitated by pouring water. Manure in the form of compost is obtained by this method.These manure are used in the fields. It is considered better than the chemicals used as fertilizers because it does not causes pollution.


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.

To develop compost first a pit is dug up and vegetable wastes and animal wastes like dung are put into the pit. A layer of soil is used to cover them. Therefore, there will be no bad odour and flies. The decomposition is facilitated by pouring water. Manure in the form of compost is obtained by this method. These decomposed matters are used as manure. Since it is from organisms, it is simple recycling of nutrients through soil. Crops, especially vegetables and fruits, grown by using manure are considered safe as compared to crops grown by using chemical fertilizers.

Test Your Skills Now!
Take a Quiz now
Reviewer Name