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Saturday, September 25, 2010

CHEMISTRY IN DAILY LIFE

WHAT WE HAVE LEARNT
$ Medicines, insecticides, textiles and food materials that we use
in daily life are chemical substances.
$ Cement is used for building purposes becauses it has the ability
to 'set' when mixed with water.
$ Natural rubber is the exudation from rubber plants.
$ Polymers are very large molecules formed by the combination of small molecules.

CHEMISTRY IN DAILY LIFE
We live in a world of matter. From the food that sustain our lives to various
objects that have built up our physical culture, everything is made up of matter.
The human body itself is a mixture of matter of differing types. The humans
who used materials obtained from nature for centuries, later made new
materials out of these to suit their needs. Now the humans have thousand of
materials for their use - both natural and human made. The ability that
humans acquired to make new materials from natural materials is the basis
of human progress. When the structure of the material world and the nature
of physical and chemical changes in them were studied, humans were able to
make new materials and to control their different properties. The development
of chemistry made this progress possible. The contribution of chemistry to
fields like, agriculture, industries, health care, food industry, habitat,
transport and research has been invaluable. Through chemical processes that
scientists develop chemistry comes up every day with answers to ever
increasing human needs.
Polymers
Cotton is the material used for the
manufacture of clothes for our daily use. Clothes
are made by weaving together thick strands that
are obtained by twisting together delicate fibres.
Different kinds of fibres are utilized for different
purposes.
$ Cotton
$ Coconut fibre
$ Jute
$ Silk
The hair of animals, paper, wood and
rubber also contain such fibres. The varied
properties of such fibres are due to the
polymers present in them. From very early
times, humans have been using many polymers
that are obtained from plants and animals. In
modern times, we have been able to make
substances that are similar, and with better
qualities with the help of chemistry.
Some natural and human made polymers
that are used in daily life are given below.
Human-made Natural
$ plastic rubber
$ polythene cellulose
$ nylon starch
$ rayon silk
$ teflon wool
Table 5.1
Chapter 05
60 Chemistry
The protein known as insulin is a small
polymer formed by joining about fifty amino acid
units. In big polymers, hundreds of different units
may be joined in different ways. The form,
hardness, strength, heat-enduring capacity and
elasticity of a polymer can be changed by
incorporating alterations in the constituents of the
polymer and in the way in which these units are
connected. For example, by heating natural
rubber with sulphur, we get a stronger form of
rubber. This happens when the polymers
contained in natural rubber become new
polymers with the addition of sulphur.
In the manufacture of polymers, monomers
are allowed to undergo chemical reactions and
get united to each other.
Chemical equations showing the formation
of some polymer molecules are given below.
n CH2 = CH2 → [ CH2 - CH2 ] n
ethylene polyethylene
n CH2 = CH [ CH2 - CH ] n
| |
Cl Cl
Vinyl chloride Polyvinyl chloride (PVC)
Here, monomers combine and form
polymers. The polymer is named by prefixing
the word 'poly' to the name of the monomer unit.
Eg : polyethylene, PVC.
There is only one kind of monomer
molecules. Polyethylene, PVC, rubber etc.
are formed by same type of monomers.
They are formed by different types of
molecules.
Living polymer factories
We have started making polymers since
only the last two years. But for
centuries we are familiar with two
living beings who make and use
polymers, the spider and the silk worm.
The web of a spider and the silk fibre of
a silk worm have always aroused the
curiosity of humans. Both are
polymers. In 1665, a scientist, Robert
Hook, declared that if certain suitable
gum-like substances are drawn out as
thin fibres, substances similar to spiderweb
and silk fibre can be made. This
method is still used to in the industrial
production of polymers.
Rubber
Rubber is a naturally available elastic
polymer. There are double bonds in its
polymer molecules. To change the properties
of rubber, changes are to be made in the
structure of its polymer.
If sulphur is added to rubber and heated,
its shape can be maintained and its hardness
increased. The process of heating rubber with
sulphur for the betterment of its properties, is
called vulcanisation. In this process, the
various chains in rubber are joined using
sulphur.
Vulcanisation enhances the following
properties of rubber.
$ tensile strength
$ hardness
$ elasticity
$ ability to withstand heat changes
Chemistry in daily life
Standard 10 61
These properties can be varied by
changing the quantity of sulphur, temperature
and time taken for vulcanisation. When we
heat rubber adding 40-45% sulphur, we get
ebonite, a substance with low elasticity.
With the growth of chemistry, we have
been able to make artificial rubber with better
qualities than natural rubber in the laboratory.
Analyse the differences between natural rubber
and synthetic rubber given in table 5.2.
Natural rubber Synthetic rubber
Low hardness high hardness
easily flammable not easily
flammable
Dissolves in Does not react
organic solvents with organic
solvents
Loses stability at Keeps stability at
high temperature high temperature
Less elastic More elastic
Table 5.2
Some commonly used synthetic rubbers,
their properties and uses are given in table 5.3.
Plastics
Different kinds of plastics are familiar to you.
These are also polymers. Plastics are now used
as substitute for wood, stone and metals in many
instances. Prepare and present a project about
the various possibilities of use of plastic objects
and the problems of excessive usage.
Burn a piece of polyester cloth, cool it and
feel it. Does it melt if it is burned again? Repeat
the activity using a polythene cover and record
the results of your observation in your science
diary. You can experiment using the following.
$ nylon rope
$ buttons
$ PVC pipe
$ bottle caps
You have understood that polyester, on
burning, underwent a chemical change and
polythene, a physical change. Plastics that
undergo a chemical change when heated are
Synthetic rubber Property Uses
Styrene butadiene High frictional force tyres
rubber (SBR) Not easily broken foot wears
Resists ozone
Gets easily oxidised
Neoprene rubber Not easily flammable Cable insulation
Does not easily react with oils Conveyer belt in coal
and solvents mines
Stable at high temperature Making hose
Thiokol High elasticity Tanks for storing solvents
Hardness Making seal
Doesn't dissolve in organic solvents
Table 5.3
Chapter 05
62 Chemistry
known as thermosetting plastics and those that undergo a physical change on heating, are known as
thermoplastics. These are listed in the table below.
Name Monomer unit Properties Uses
Thermoplastics
Poly ethylene ethylene Insulator as insulator, as wrappers
( CH2 - CH2 ) n CH2 = CH2 Flexibile for making pipes
Polyvinyl chloride Vinyl chloride insulator manufacturing of pipe, tanks
[ CH2 - CH ] n CH2 = CHCl for chemical process, rain
| coat, helmets etc.
Cl
Nylon Adipic acid and has lusture Fishing nets, clothes,
Hexamethylene strong parachutes, chords etc.
diamine firm
elastic
Thermosetting plastics
Bakelite Phenol + Insulator, making switches,
formaldehyde black in colour soap dishes,
electrical appliances etc.
Polyester Esters of Low density Making body of vehicles
unsaturated Transparent home appliances,
alcohols Strong and firm clothes etc.
Table 5.4
Since thermoplastics become soft on
heating, they can be used again (recycling) to
make new things. Thermosetting plastics cannot
be used again, Why? Try to find out the various
uses of the two types of plastics and the
differences in their properties.
Fibres
Centuries ago, humans learned to make
strong and beautiful things from the thin natural
fibres like coconut husk, cotton, hemp, silk
and animal hair. Before the emergence of
modern technology, such materials were used
by us. All of them are polymers. Polymers of
plant origin are made of cellulose and those of
animal origin with proteins. Though these
polymers could be used for different purposes,
their basic qualities could not be changed.
With the development of modern chemistry we
were able to study more about the qualities of
such substances and make them artificially with
better qualities. Artificial fibres are an
important contribution of polymer chemistry.
Many artificial fibres with wide variety in
qualities like colour, strength, weight, reflective
property, ability to maintain shape and
smoothness are now industrially made. The
astonishing variety in the clothes that we now
use is due to the growth of chemistry.
Chemistry in daily life
Standard 10 63
Figure 5.1
Artificial Fibres
Rayon is regenerated cellulose.
Substances that contain cellulose (e.g. wood
pulp) are first dissolved in carbon disulphide
and then made into pulp by adding alkali. This
is viscose. This viscose is then passed
through very small holes into a dilute acid
solution. In this acid solution, the cellulose
fibres are regenerated. This is known as
artificial silk.
Glass
Glass is one of the widely used substances.
What are the commonly used objects made of
glass?
$ lenses
$ utensils
$
$
Glass is used to make various household
utensils and laboratoryware. The windshield
of a motor vehicle is also made of glass. Are
the properties of all these glasses similar?
Table 5.5 shows different types of glasses, their
constituents and uses.
Examine the table, find out the difference
in properties of each type of glass and record
it in your science diary. Which is the common
ingredient in the above glasses? The
ingredients needed to make soda glass, heat
resistant glass and flint glass are given in the
table. These ingredients are heated at a certain
temperature. We can make glasswares by
pouring the molten substance into moulds or
by blowing.
Safety glass is made by pressing and
binding two glass sheets with a thin plastic
sheet held in between them. These are
laminated glasses.
Fibre glass is made by passing molten
glass through very minute holes in metallic
cylinders. Fibre glass is as strong as steel.
Making artificial silk
Dissolve about 10 g of copper
sulphate in water in a beaker. To this,
add dilute sodium hydroxide. Copper
hydroxide precipitates. Remove this
precipitate using a filter paper.
Dissolve it in concentrated
ammonium hydroxide. To this
solution, add some cotton. Cotton
dissolves in it. Take this solution in
a syringe and inject it into dilute
sulphuric acid in a beaker. You get
synthetic fibres.
Chapter 05
64 Chemistry
Different colours can be given to glass
using different metallic oxides or ions.
Metal compound/ion Colour
Ferric ion Yellow
Ferrous or chromium Green
Cobalt ion Blue
Manganese dioxide Purple
Nickel salt Red
Cupric oxide Red
Cadmium sulphide Lemon yellow
Uranium oxide Greenish yellow
Cryolite/Calcium Opaque milk
phosphate white colour
Table 5.6
Cement
Cement is a man made substance that has
changed the very face of earth. It was with
the large scale manufacturing of cement that
we were able to construct big townships,
cities, factories and many types of buildings.
Cement which becomes soft when mixed with
water can be moulded into desired shapes,
subsequently sets and becomes very hard.
This is what makes cement suitable for
construction works.
What is cement?
Cement is a complex mixture of aluminates
and silicates. Given below are the raw
materials used for this (Table 5.7).
Table 5.5
Chemistry in daily life
Standard 10 65
Manufacture of cement
The raw materials are ground into a fine
powder and mixed in the fixed proportion.
This is heated in a furnace at a high temperature
(15000C). Clinkers, which is a complex
mixture of calcium silicate and calcium
aluminate is formed. Gypsum is added to
clinker and the mixture is powdered to make
cement.
The portland cement that we use
commonly contain the following ingredients.
(Table 5.8).
Cement of olden days
A building material with properties similar to cement was widely used in the past.
This substance is made from lime and is known as slaked lime. When sea shell or
lime stone which contain CaCO3 is strongly heated, CO2 is liberated.
CaCO3 → CaO + CO2
Water is added to the CaO thus obtained and the following reaction takes place.
CaO + H2O
Ca(OH)2
Ca(OH)2 - slaked lime - can be shaped as one likes and used for construction works.
Subsequently, on reacting with the CO2 in the atmosphere, it becomes CaCO3 which
is very firm.
Ca (OH)2 + CO2
CaCO3 + H2O
The process which starts with CaCO3 and ends with the same substance.
Table 5.8
Compound Chemical
composition %
Lime CaO 60-67
Silica SiO2 17-25
Alumina Al2O3 3-8
Iron oxide Fe2O3 0.5-6.0
Magnesia MgO 0.1-4.0
Sulphur trioxide SO3 1-2
Soda + potash Na2O + K2O 0.5-1.3
Table 5.7
Compound Chemical composition Percentage
Elite 3 CaO.SiO2 40 - 65
Belite 2 CaO. SiO2 10 - 25
Aluminate 3 CaO Al2O3 Up to10
Ferrite 4 CaO.Al2O3.Fe2 O3 Up to 10
Gypsum Ca SO4. 2 H2O Upto 2 – 5
Chapter 05
66 Chemistry
Action with water
Have you ever thought how cement hardens
when water is added? Many reactions take place
at the same time when water is added to cement.
The aluminates and silicates in cement react with
water and undergo hydration. The hydration of
aluminates takes place very fast. This is the
"setting of cement."
3CaO.Al2O3 + 6H2O → 3CaO.Al2O3
6H2O + heat energy
Substances like gypsum can control the
setting time. You can now explain why gypsum
is added to cement during its manufacture. Is
the setting of cement exothermic or endothermic?
The mixture of cement, sand and water is
called cement mortar. You are familiar with its
use in building construction.
Gravel is added to cement mortar to increase
its strength. This mixture is known as concrete.
This can again be reinforced using steel or iron
rods.
Medicines
The living body is made of chemical
substances. Any foreign chemical substance
that enters a living body can hence react with
body tissues and fluids. By inducing suitable
chemical reactions in the body through
chemicals, diseases can also be controlled.
Chemicals used in this way are known as
medicines. Chemistry helps in identifying
chemical substances that can control disease.
Chemicals that can react with protein
molecules are usually used as medicines. All
the processes in the living body are controlled
through enzymes which are proteins. This is
why chemicals that react with proteins are used
as medicines. For example, when antibiotics
react with enzymes in the bacterial cell they
are destroyed or their growth stopped.
There are certain receptors on the cellsurfaces
which can receive chemical messages
that come from nerves and, also, react with
hormones. These are also proteins. It is
through the reactions with these that medicines
attain the intended effect. Analgesics (pain
killers) work in this way.
From nature to chemistry
Alexander Fleming discovered penicillin
in 1929. This medicine, which could
destroy bacteria, was extracted by him
from a mold. Medical science was able
to eradicate and control many lethal
diseases through this medicine. Though
it was Alexander Fleming who gave us
this medicine that could save the life of
millions of people, chemistry too has a
claim in this success.
Since the quantity of penicillin
separated from mold was very little, it
was sold by pharmaceutical companies
at very high prices. Very soon scientists
discovered techniques to synthesise
penicillin. The anti-bacterial properties
were analysed and scientists were able
to synthesise chemicals with similar
properties. This was made possible by
the progress of chemistry. Chemistry
has enabled us to make many new
medicines.
Chemistry in daily life
Standard 10 67
Along with the ability to conduct such
reactions, chemicals that are used as medicines
must be those that do not cause damage to
other cells and chemical systems.
Antibiotics
Certain chemicals produced by bacteria,
fungus etc. destroy other micro oganisms or
hinder their growth. These are called
antibiotics. Penicillin is an antibiotic that is
widely used. The names of some antibiotics
are given below:
$ penicillin
$ tetracycline
$ ampicillin
$ amoxicillin
$ chloramphenicol
Chloramphenicol is an antibiotic that is
effective against many disease-causing germs.
Since this substance is easily absorbed in the
alimentary tract, this is applied as oral medicine
in diseases like typhoid, cholera, meningitis,
pneumonia etc.
$ Though medicines greatly help protect
and maintain our health, does not their
indiscriminatory use bring about
dangerous side effects?
Discuss the above and conduct a seminar.
Agriculture and chemistry
Agriculture is another field where
revolutionary changes have come about
through the growth of chemistry. When world
population increased rapidly, the need for food
materials also increased. It was impossible to
cater to this increased need through traditional
ways of agriculture. Through modern methods
of farming, food production multiplied tenfold.
'Green revolution' could take place in a country
like India. It was through the application of
knowledge of chemistry that the methods of
farming could be improved. The most
important factor in the modernisation of
agriculture was the use of fertilizers which
helped the growth of plants. What are
fertilizers? How do they act?
Fertilizers
Plants get elements like carbon, hydrogen,
oxygen etc. which are essential for their
growth, from the atmosphere and water.
Besides these elements, sodium, potassium and
phosphorous and small quantities of calcium,
magnesium and sulphur are also needed.
Fertilizers are used mainly to provide these
elements. The elements contained in the soil
are lost through rain water and repeated
farming. Elements needed by the plants can
be immediately made available through
fertilizers. It has been observed that
agricultural yield more than doubles if fertilzers
are used in the proper way.
Nitrogen, phosphorous and potassium are
the most important constituents of fertilizers.
Fertilizers are classified into three types -
nitrogen fertilizers, phosphorous fertilizers and
potassium fertilizers. The problems that arise
due to lack of these elements and the fertilizers
that can be used in such situations are given in
table 5.9 below.
Chapter 05
68 Chemistry
$ chlorination
$
How is water purified by chlorination? Find
out and write it in your science diary.
Chemicals that are used to kill harmful
virus, fungus etc. are called germicides. Find
out more examples.
Like human beings, plants too have
enemies and diseases. Worms, insects,
rodents and weeds are some of these. To
protect the plants from these, we use many
chemicals. These chemicals pollute our soil,
water and air and many harmful effects have
become apparent. Do you know that many
insecticides pose grave threats to generations
of humans and destroy whole ecosystems?
$ Do the insecticides that we apply to the
soil decompose and perish?
$ Does their use cause air pollution?
$ Do they cause water pollution?
$ How do they affect our ecosystem?
$ To avoid this, can you propose
alternatives?
Table 5.9
Element Problems caused by deficiency Fertilizer containing
of the element the element
Potassium Yield and disease resistence reduced Potassium chloride
Potassium sulphate
Nitrogen Cannot make proteins Sodium nitrate, Calcium nitrate,
Ammonium nitrate
Ammonium sulphate
Phosphorous Yield reduced, Fruits does not ripen easily Bone powder
Ability to absorb nitrogen and other Calcium phosphate
elements reduced
Find out the percentage composition of
nitrogen in different nitrogen fertilizers. Can
you say which fertilizer is the better one?
Insecticides
You know that insecticides have had a
great impact in the field of agriculture. Tabulate
the various insecticides and their uses.
Insecticides Uses
1. DDT Control mosquitoes
Baygon and flies
2. Parathion Kills insects that
Sevin destroy crops
3.
4.
Weed killers
These are chemicals that destroy the
weeds.
Eg: Treflan
Calcium cynamide
Germicides
You have heard of purification of drinking
water. What are the methods for this?
Chemistry in daily life
Standard 10 69
SUMMARY
$ Thermoplastics are those that undergo physical changes when heated.
$ Thermosetting plastics are those that undergo chemical changes when
heated.
$ Natural rubber is a polymer obtained from nature.
$ Vulcanisation is the process of improving the properties of rubber by
adding sulphur and heating it.
$ Glass is a mixture of silicates.
$ The compounds of transitional elements can provide colour to glass.
$ Cement is a mixture of silicates and aluminates.
$ The ‘setting’ of cement is due to the hydration of aluminates and
silicates.
$ Pharmaceutical chemistry is of great importance. Chemistry has
contributed greatly in the manufacturing of fertilizers, insecticides,
fungicides, weed killers etc. in the field of agriculture.
$ Chemicals which have the ability to react with proteins are commonly
used as medicines.
$ Fertilizers, insecticides, weed killers and germicides which are the
contributions of chemistry have greatly helped in the improvement of
agriculture.
1. Conduct a study on the dyes used in cotton
and polyester clothes.
2. Find out the chemical ingredients of
insecticides that are commonly used.
3. Write the balanced equation for making
polypropylene.
4. Find out and list the uses of ebonite.
MORE ACTIVITIES FOR YOU
$$$$$$
5. Why is flint glass used for making lenses?
6. Find out the common ingredient in medicines
used for fever.
7. Polythene is not used for making handles of
cooking vessels. Can you explain the
reason?
8. Why is water sprayed repeatedly after
cement plastering has been done?

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