science 10

d. It is bad conductor of heat and electricity.

These characteristics are regarded as the advantages of plastics
over other appliances.

Types of plastics
There are two types of plastics. They are as follows:

1. Thermoplastics
2. Thermosetting plastics

Thermoplastics

The plastics which become, soft on heating and can be moulded
again and again is called thermoplasties. It becomes because soft on
heating the long chains lie close to each other but are not strongly
connected. They harden again on cooling. So, they can be moulded
several times into different shapes Polythene is the most common
thermoplastic. The other thermoplastics are polystyrene, polyester,
polyvinyl chloride, etc. The thermoplastic is used for making buckets,
bags, pipes, ropes, etc.

Polythene

It is a polymer of ethylene which can be made by heating ethylene

under high pressure in the presence of a catalyst. It is hard but

flexible and strong. It is used for making buckets, pipes, laboratory

apparatus, kitchen wares, toys, and several other household items.

n(CH2 = CH2) ↑temp,↑press [CH2 - CH2]n
catalyst

ethene Polyethene

Polyvinyl chloride (PVC)

The polymerization of vinyl chloride produces polyvinyl chloride. It
is used for making pipes, raincoats, boots, curtains, hand bags, seats,
furniture, soles of shoes, buckets and insulating cover for electrical
wiring.

n(CH2 = CHCl) polymeriztion → -[CH2 - CHCl]-n

Vinyl chloride Polyvinyl chloride (PVC)

Polystyrene
Polystyrene is a polymer of styrene molecule. It is a hard transparent

247 Times' Crucial Science Book - 10

and glass-like plastic. It is used for making toys, themosflask, ceiling
tiles and pipes etc. It is a also used as insulator.

Thermosetting plastics

The plastic that cannot be softened again once a particular shape is
given to it is called thermosetting plastics. Thermosetting plastics are
usually hard and strong. They do not bend easily and are resistant to
heat. So, these plastics cannot be moulded a second time.

Bakelite and melamine are the examples of thermosetting
plastics. Bakelite is manufactured by condensation polymerization of
formaldehyde and phenol. It is used for making radio and TV cabinets,
plugs and other electrical fittings, switches, handles of cookers and
tea kettles etc. Melamine can be coloured easily. It is used to make
cups, plates, bowls, saucers, etc.

Differences between thermoplastics and thermosetting plastics

Thermoplastics Thermosetting plastics

1. It can be reshaped according 1. It cannot be reshaped according

to desire. to desire.

2. It readily softens on heating. 2. It does not soften on heating.

3. These plastics are usually 3. They are usually hard, strong

soft and weak. Examples : and brittle. Examples:

polythene, PVC etc. Bakelite, melamine etc.

Advantages and disadvantages of plastics

As discussed above, plastics are widely used because of their several
properties such as lightness, durability, able to be shaped again and
again, etc.

Besides having advantages, plastics have disadvantages too. They are:
1. They are non-biodegradable. This means that they do not
decay and cause pollution.

2. Many plastics often produce poisonous gases and smoke on
burning and thus cause air pollution.

3. Some plastics catch fire very easily and cause fire of house,
factory, etc.

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Fibres

A fibre is a long hair like polymeric strand which is strong and
flexible. Fibres are of two types: natural and synthetic fibres.

Natural fibres

Cotton, silk, wool, linen, etc are natural fibres. Cotton is obtained
from cotton plant, silk from cocoon of silkworm, wool generally from
sheep and rabbit, and linens from stalk of flax plant. Similarly, simal,
hemp, coconut plant, etc also give fibres.

Cotton fibres are used to make clothes. Silk is also used for making
clothes. Wool is used for making blankets, clothes, etc. Similarly,
linen is also used for making clothes. Jute, hemp and coconut are
coarse plant fibres which are used to make ropes, sacs, bags, etc.

Advantages of natural fibres
1. The cotton clothes absorb sweat. They allow air to circulate
and help to keep our body cool. So, these clothes are
comfortable to wear in summer.

2. The woolen clothes are comfortable to wear in winter. They
do not allow body heat to escape and keep us warm.

Disadvantages of natural fibres
1. They are expensive but not durable.

2. Cotton clothes need ironing after every wash.

3. Woolen clothes are easily destroyed by insects.

4. The fabrics made from natural fibres may shrink on washing.

5. They do not get dried fast after washing.

Synthetic fibres

The fibres which are produced artificially by chemical reactions are
called synthetic fibres. Some of the common synthetic fibres are
nylon, terylene, rayon, orlon, cashmilon, acrylic fibres, fortel, coddle,
cresian, etc. The advantageous properties of synthetic fibres are as
follows:

1. They are fine, light and durable.
2. They dry up easily after washing.
3. They are strong and flexible.

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4. They are not attacked by insects and fungi.

Rayon

It is a synthetic fibre but resembles silk in appearance and hence
it is also called artificial silk. Rayon is manufactured from cellulose.

Uses Rayon is used in the manufacture of fabrics like sarees.
1.
2. It is also used to manufacture bandage and lint (for dressing
wound).

Nylon

It is the first prepared synthetic fiber. Nylon is a polymer formed
by the polymerization of adipic acid and hexamethylene diamine.
Hence, nylon fibres are also known as polyamides.

Nylon is a light and strong elastic fibre. It absorbs very little water,
so it dries up rapidly after washing. It does not shrink and is not
attacked by insects.

Uses It is used for making tyre cords, ropes, parachutes, bristles of
1. paint brushes, etc.

2. It is used for making sarees, shirts, shocks, etc.
3.
It is also used for making carpets, fishing nets etc.

Terylene (polyester)

It is a strong, flexible, durable and wrinkle resistant fibre. It is also
resistant to the action of chemicals. It dries up quickly because it
absorbs less water while washing. It is not damaged by insects.

Uses It is used for making textiles, suits etc.
1. It is also used for making sails for boats.
2.

Disadvantages of artificial fibres
1. The clothes made of artificial fibre catch fire easily.
2. They absorb less sweat.
3. They produce bad smell on burning and pollute the air.

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4. They are non-biodegradable and pollute the environment.

Soaps and detergents

Soap is a cleaning agent. It is produced by the hydrolysis of oils
and fats. The oils and fats are the triesters of glycerol with long
chain fatty acids. The main fatty acids present in fats and oils are
palmitic acid (C15H31COOH), stearic acid (C17H35COOH), oleic acid
(C17H33COOH), etc.

Soap is the sodium salt of long chain fatty acid which has cleansing
property in water. The soap is produced when an oil or fat is heated
with strong alkali solution.

CH2 OOCR + Na OH CH2 OH
| |

CH OOCR + Na OH → CH OH + 3RCOONa

|| Soap

CH2 OOCR + Na OH CH2 OH

Fat or Oil Sodium hydroxide Glycerol

Where, R represents the alkyl radical such as C17H35, C15H31etc.

The process of making soap by hydrolysis of fats or oils with strong
alkali solution is called saponification.

During saponification, sodium chloride is added in the solution to
precipitate. After precipitation, soap floats on the surface of water
due to its less density. It is then collected and kept into moulds to get
the soap cakes. Sodium carbonate or starch is added to make the soap
hard. Additional materials such as perfumes, colours, antiseptics and
bleaching materials are also added in the soap according to the need.

Detergents

The sodium salts of long chain benzene sulphonic acid or long chain
alkyl benzene sulphonates are called detergents. The detergents are
cheap with more cleansing property. Some common examples of
detergents are sodium lauryl sulphate, alkyl benzene sulphonate,
sodium pyrophosphate, etc. The detergents are better than soaps
due to the following reasons:

1. Synthetic detergents have a stronger cleansing action than

251 Times' Crucial Science Book - 10

that of soap.
2. They are cheaper because they are prepared from the

hydrocarbons produced as byproducts of petroleum.
3. They work well even with hard water but soaps are insoluble in it.

Detergent is also known as soapless soap because it has cleansing
property like that of soap but it does not contain actual soap.
Detergent powder contains synthetic detergents (15-30%), sodium
carbonate, sodium silicate, sodium sulphate and little amount of
bleaching agents. Perfume is also added to make washing powder
more attractive and popular. The main disadvantage of detergents is
that they are non-biodegradable and hence pollute the environment.

Differences between soaps and detergents

Soaps Detergents

1. Soaps are sodium salts of 1. Detergents are the sodium salts

long chain fatty acids. of long chain benzene sulphonic

acid.

2. They are prepared from 2. Theyarepreparedfromhydrocarbons

oil or fat of animals or obtained as the by-products of

plants. petroleum.

3. T h e y h a v e 3. They have relatively strong
relatively weak cleansing action.
cleansing action.

4. They are mostly 5. They are mostly non-biodegradable.
biodegradable.

Pesticides

The pesticides are the poisonous substances which are used to kill
pests. The pests destroy the crops and decrease the yield. Pesticides
are of different types: insecticides, herbicides, fungicides, rodenticides,
etc that are used to kill insects, weeds, fungi and rodents respectively.

Insecticides

The poisonous substances which are used to kill harmful insects are
called insecticides. The insects harm the crops, domestic animals
and human being. So, they are killed by using insecticides. The
insecticides can be categorized into two types:

1. Organic insecticides 2. Inorganic insecticides

Times' Crucial Science Book - 10 252

1. Organic insecticides

Organic insecticides are the synthetic compounds which are
composed of carbon, hydrogen, oxygen and other elements. There
are three types of organic insecticides. They are:

a. Chlorinated organic insecticides: These compounds
contain chlorine as an additional element. These compounds
are stable and have long term effects. For example, aldrin,
dieldrin, dichlorodiphenyl trichloroethane (DDT) and benzene
hexachloride (BHC).

b. Organophosphate insecticides: The organic insecticides
that contains phosphorus as an additional element are called
organosphosphate insecticides. These insecticides are less stable,
degradable and highly toxic to other animals. For example,
malathion, parathion, phosdrine, etc.

c. Carbamate insecticides: The insecticides which have amino
group (–NH2) in their molecular formula, are called carbamatc
insecticides. For example, baygon and termic.

2. Inorganic insecticides

They are made from minerals and do not contain organic groups.
For example, calcium arsenate, lead arsenate, fluorides and lime
sulphur. These inscecticides are used to protect cotton, fruit,
vegetables, etc from insects.

Characteristics of good insecticides

1. They should be biodegradable.

2. They should not be harmful to human beings, birds and
higher animals.

3. They should not pollute air, water or soil.

4. They should not leave long term effects.

Advantages of insecticides

1. They kill or control harmful insects or pests.

2. They help to increase food production.

3. They help to control several diseases by killing germs.

Disadvantages of insecticides

1. Insecticides kill not only harmful insects but also some useful

253 Times' Crucial Science Book - 10

insects.

2. They are mostly synthetic and non-biodegradable.

3. DDT is a stable and non-biodegradable insecticide with long
term effects. Hence, it harms human beings, animals, birds
and plants. DDT causes air, water and soil pollution. If it enters
human body through contaminated food, it badly affects liver,
kidney and other organs. It also affects the bird's eggs.

4. They can leave harmful deposits in fruits and crops while
using in them.

Precautions while using insecticides
1. We should be very careful while applying insecticides because
they can take our lives as well.
2. They should be kept away from the reach of children.
3. They should not be stored along with or near the foodstuffs.
4. We should wash our hands well with soap and water after
using insecticides.
5. Excessive use of insecticides should be avoided.

Fertilizers

Fertilizers are the substances which are added to the soil to increase
the crop production by supplying essential nutrients. There are two
types of fertilizers:

a. Organic fertilizers (manures) b. Chemical fertilizers

a. Organic fertilizers

The fertilizers which are obtained from the decomposition of the
animal wastes and the dead plants are called organic fertilizers.
Compost is an example of organic fertilizer. It is prepared by
keeping dead plants and animal wastes buried in a pit with
thin layers of soil. The organic matter is decomposed by micro-
organisms to give compost.

Advantages
a. They are biodegradable and hence do not cause pollution.
b. They are useful for all varieties of plants.
c. They are cheap as they are produced from wastes.
d. They do not impart side effects on human beings as done by
chemical fertilizers.

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Disadvantages
Organic fertilizers are poor in inorganic nutrients like nitrogen,
phosphorus and potassium.

b. Chemical fertilizers

The water soluble chemical compounds which are added to the
soil to increase crop production by supplying essential elements
are called chemical fertilizers. The chemical fertilizers supply
nitrogen, phosphorus, potassium, etc to the soil. The examples
of chemical fertilizers are ammonium sulphate, ammonium
phosphate, urea, potassium nitrate, etc.
Some chemical fertilizers

1. Nitrogen containing fertilizers

Name of fertilizer Formula
Ammonium sulphate (NH4)2SO4
Ammonium nitrate NH4NO3
Urea CO(NH2)2

Functions of nitrogen

a. It helps in rapid growth of plants.
b. It helps to increases the crop yield.
The deficiency of nitrogen in plants causes following symptoms:
a. Reduced size of fruits and seeds.
b. Reduced and yellow leaves in plants.
c. Reduction in crop yield.
2. Phosphorus containing fertilizers

Name of fertilizer Formula
Ammonium phosphate (NH4)3PO4
Super phosphate Ca(H2PO4)2. 2CaSO4
Triple super phosphate 3Ca(H2PO4)2
Bone meal --

Function of phosphorus

a. It is needed for the growth of leaves, buds and roots.
b. It is essential for protein synthesis and cell division.
c. It helps in developing seeds in crops.
d. It helps in ripening the fruits.

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3. Potassium containing fertilizers

The chloride, nitrate and sulphate of potassium are the potassium
containing fertiligers. Potassium containing fertilizer is called
potash fertilizer.

Name of fertilizer Formula
Potassium chloride KCl

Potassium nitrate KNO3
Potassium sulphate
Ash K2SO4
–

Function of potassium

a. It helps in protein synthesis and cell division.
b. It helps in preparing food for plants.
c. It increases disease resistant capacity of plants.
The fertilizer which contains all three primary nutrients, i.e, nitrogen,
phosphorus and potassium is known as NPK fertilizer.

Differences between organic fertilizers and chemical fertilizers

Organic Fertilizer Chemical Fertilizer
1. They are man-made chemicals
1. They are obtained by
the decomposition of which contain specific
dead plants and animal elements.
wastes.
2. They are soluble in water and
2. They are not readily hence are quickly absorbed by
soluble in water and plants.
are absorbed slowly by
plants. 3. They are nutrient specific. For
example; nitrogen containing
3. They are not nutrient fertilizers provide only
specific. They provide nitrogen.
several nutrients.
4. They pollute the environment.
4. They do not pollute the
environment. 5. They are rich in nitrogen,
phosphorus and potassium
5. They are rich in organic (NPK). They do not provide
nutrients but poor in organic nutrients.
nitrogen, phosphorous
and potassium (NPK).

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Chemical pollution

The pollution of the environment due to the release of unwanted
and harmful chemicals is called chemical pollution. The chemical
pollution is heavy in industrial and densely populated areas. The
chemical pollution is harmful to human as well as other lives.

Causes of chemical pollution

The use of pesticides, chemical fertilizers, plastics, detergents, etc is
the main cause of chemical pollution. In addition to these, industrial
wastes and byproducts, water from the science labs and hospitals are
also the major causes of chemical pollution.

The major causes of chemical pollution are as follows:

1. Chemical fertilizers: The chemical fertilizers contain useful
as well as harmful substances. The harmful elements present
in chemical fertilizers are accumulated in fruits, vegetables and
grains. These elements harm human health if such foods are
eaten.

The chemical fertilizer washed away by run off water from the
field is mixed into the rivers, ponds, lakes, etc. Algae and other
aquatic weeds grow rapidly in such water bodies and take up
more oxygen dissolved in water. Thus, the aquatic animals begin
to die due to the lack of oxygen.

2. Insecticides: The insecticides such as DDT, malathion, aldrin,
dialdrin etc cause chemical pollution. DDT is accmulated in the
body of animals and causes long term effects. If other carnivorous
animals eat the animal died from the effect of DDT, they are also
affected.

3. Detergents: Detergents and other synthetic cleansers are non-
biodegradable. They are harmful to human health, if swallowed
or came in contact of them.

4. Colouring matter in foodstuff: The colouring matter used in
tea, coffee, chocolate, sweet dishes, etc are harmful to human
health. These chemicals can make us prone to dangerous diseases
like cancer. These chemicals also affect the vital organs such as
kidney, liver, etc.

5. Plastics: Plastics are non-biodegradable. So, they pollute the
environment. The burning of plastics produces poisonons gases

257 Times' Crucial Science Book - 10

and causes air pollution.

6. Harmful gases from vehicles and factories: The harmful
gases such as CO2, SO2, NO, NO2, CO, etc are emitted from
factories and vehicles. These gases cause air pollution and
adversely affect the human health.

7. Domestic wastes: The wastes produced from home is one of
the major causes of pollution in urban areas. When the toxic
substances present in the wastes spread in air and water, they
enter human body and cause serious harms.

Control measures of pollution

Various human activities are responsible for causing pollution
hence, it is not easy to make our environment pollution-free. Public
awareness, feeling of responsibility and organized efforts are
necessary to control pollution.

Some of the control measures of pollution are as follows:
a. The gases emitted from factories and vehicles should be
converted in to harmless form before they are released to the
environment.
b. The use of plastic bags should be discouraged. Plastic
materials should be recycled instead of throwing them as
waste.
c. The overuse of pesticides and chemical fertilizers should be
controlled.
d. Household waste should be managed properly.
e. People should be made conscious about the use of harmful
colours in foodstuffs.

It is necessary to keep balance in nature. Hence, every individual
should be conscious and responsible for the preventive measures of
pollution. Control of pollution, and conservation of nature help to
keep balance in nature.

Learn and Write

1. Hard glass is also called potash lime glass. Why?

Hard glass is prepared by heating mixture of silica, potassium
carbonate and calcium carbonate at high temperature. Thus,
hard glass contains potassium silicate and calcium silicate.
Therefore, hard glass is called potash lime glass.

Times' Crucial Science Book - 10 258

2. Sodium chloride powder is sprayed on the ceramics pots when
it is hot. Why?

When sodium chloride powder is sprayed in the ceramic pots
when it is hot, it makes them smooth nor-porous and water
proof.

3. Environmentalists advise not to use detergents. Why?

Detergents are non-biodegradable. Thus, they do not decay
for a long time and cause environmental pollution. Therefore,
environmentalists advise not to use detergents.

4. Use of insecticides is both beneficial and harmful. Why?

Insecticide kills the harmful insects which destroy crops. Thus,
it helps to increase crop production. It does not kill harmful
insects only but also useful insects. Therefore, it is harmful too.

Main points to remember

1. Cement is a mixture of calcium silicate and calcium aluminate
in the form of fine grey powder.

2. Glass is an amorphous, hard, transparent and homogeneous
mixture of silicates of different metals. It may contain third
substance as colouring matter.

3. A special type of clay which contains the compounds of carbon,
nitrogen, silica and oxygen is called ceramics.

4. A polymer is an extremely large molecule that is formed by the
chemical combination of a large number of small molecules together.

5. The process by which two or more simple molecules are joined
together to form a giant molecule is called polymerization.

6. There are two types of fibres natural fibres and artificial fibres.
7. Soap is the sodium salt of long chain fatty acid which has

cleansing property in water.
8. The process of making soap by the hydrolysis of fats or oils with

strong alkali solution is called saponification.
9. Detergents are the sodium salts of long chain benzene sulphonic

acid or long chain alkyl benzene sulphonates.
10. Fertilizers are the substances which are added to the soil to

increase the crop production by supplying essential nutrients.
11. The chemical fertilizers which contain nitrogen, phosphorus

and potassium are called NPK fertilizers.

259 Times' Crucial Science Book - 10

Exercise

A. Choose the best alternative.

1. Principal raw material for the manufacture of cement

a. Clay b. Gypsum c. Limestone d. Alumina

2. The mixture of calcium aluminate and calcium silicate in the
form of small reddish balls is called

a. Cement clinker b. Mortar c. Concrete d. All of these

3. The metallic oxide which gives green colour to the glass is

a. Chromium oxide b. Nickel oxide

c. Cobalt oxide d. All of these

4. Pure white soil used in ceramics is called

a. Kiln b. Kaolin c. Silicate d. Iron oxide

5. Sodium salt of long chain benbzene sulphonic acid

a. Soap b. Polystyrene c. Pesticide d. Detergent

B. Answer these questions in brief.

1. Write down the raw materials of the following substances:

i. Cement ii. Glass iii. Borosilicate glass

iv. Ordinary glass v. Soap vi. Hard glass

vii. Water glass viii. Green coloured glass

2. Why are the following chemicals added while making these
materials?

i. Gypsum in cement.

ii. Calcium carbonate in ordinary glass.

iii. Lead monoxide in ordinary glass.

iv. Nickel oxide in ordinary glass.

v. Salt in heated ceramics.

vi Sodium chloride in the solution during saponification.

3. Which industrial substances are formed from the following
chemicals?

i. Silica and sodium carbonate are heated together.

ii. Fat and caustic soda are heated together.

4. Name the chemicals found in cement.

5. Write down a character and a use of water glass.

Times' Crucial Science Book - 10 260

6. Which materials are used to make hard glass? Write down
properties and uses of this glass.

7. How is pyrex glass made? Which metallic oxide is used to
prepare red glass?

8. Define the terms monomer, polymer and polymerization.

9. Is compost fertilizer organic fertilizer or chemical one? Give
reasons to justify your answer.

10. Name three types of organic insecticides with one example of each.

11. What are insecticides? Why is their use discouraged?

12. Give two examples of phosphorus containing chemical
fertilizer. What is the use of phosphorus to plants?

13. What happens to the plants if there is lack of nitrogen in the soil?

14. Why is potassium necessary for plants? Name a chemical
fertilizer that supplies potassium in the soil.

15. What is NPK fertilizer? Give an example of chemical fertilizer
each containing nitrogen phosphorus and potassium.

16. Write down the name of a carbamate insecticide.

17. What is chemical pollution? Write down any four methods to
control chemical pollution.

18. Write down the full form of:

a. PVC b. BHC c. DDT d. NPK

19. Write down one advantage and disadvantage each of DDT.

C. Write down one use of each:

1. RCC 2. PVC 3. Mortar 4. Pyrex glass

5. Bakelite 6. Rayon 7. Nylon 8. Cotton fibre

D. Give reasons:

1. The lower part of the window glass becomes thicker than the
upper part after many years.

2. The equipments used in science laboratory are made of
borosilicate glass.

3. Thermosetting plastic is used to cover the handle of pressure
cooker.

4. Environmentalist request to avoid using of plastics.

5. It is better to use organic fertilizers to grow vegetables.

f. Detergent is known as soapless soap.

261 Times' Crucial Science Book - 10

6. The use of insecticides is not an interest but an obligation.
E. Write down differences between.

1. Thermoplastic and thermosetting plastic.
2. Ordinary glass and hard glass.
3. Soap and detergent.
4. Organic fertilizer and inorganic fertilizers.
5. Natural polymer and artificial polymer.

Project Work

Study the materials used in your home. Find out how they are
produced and what their constituents are. Also write down the
uses (advantages) and disadvantages of these materials.

Glossary : a specialized oven or furnace used
for industrial processes such as firing
• Kiln clay for pottery or bricks

• Homogeneous : having uniform composition
• Silica
: silicon dioxide found naturally in various
• Ceramics crystalline and amorphous forms, e.g. quartz,
• Synthetic opal, sand, flint, etc
• Accumulated
: objects that are made from clay and are made
hard with heat

: man-made

: collected

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