Download SCIENCE - II TERM (2014 – 2015) STD 7 Chemistry in Your Life

SCIENCE - II TERM (2014 – 2015)
STD 7
Chemistry in Your Life
In this chapter, you will learn about:
 Compounds and their uses including organic compounds such as hydrocarbons
 Man-made materials and their uses
Useful compounds
Compounds are the substances that are formed by elements combining in a fixed proportion.
Let us learn about some compounds which are used in daily life.
Fertilizers
Fertilizers are substances applied to the soil to promote plant growth. The main elements present in a
fertilizer are nitrogen, phosphorus and potassium. Generally, the decaying organic matter present in the
soil, supply all these minerals to the plants. But if the natural nutrient supply is not present or is insufficient,
then fertilizers must be added to the soil. Fertilizers like urea and ammonium phosphate supply nitrogen to
the soil. Potassium sulphate supplies potassium to the soil.
Pesticides
Pesticides are chemicals that are used to destroy pests such as rats, insects and disease causing organisms
like bacteria, fungi, algae and viruses that destroy plants. Some common pesticides are DDT, BHC
heptachlor and methyl parathion.
Bordeaux mixture is used to control fungus on grapes, melons and other berries. It is also used in swimming
pools to control growth of algae.
Though pesticides are used to reduce the levels of pest damage, some of them are harmful. Some pesticides
like DDT (dichlorodiphenyltrichloroethane) do not break down easily in the environment and accumulate
in food chains and spread to other ecosystems. These pesticides also cause contamination of water, which if
consumed causes health problems like birth defects, nerve damage and cancer.
To reduce harmful effects of pesticides the following steps should be taken:
1. Washing: You must wash all fruits and vegetables under tap water before consuming them. This
helps to remove bacteria and traces of chemicals from the surface of fruits and vegetables.
2. Peeling and trimming: Peel off the skin of fruits and vegetables to remove bacteria and pesticides.
1
Discard outer leaves of leafy vegetables. Trim fat from meat and poultry and fish as pesticides
accumulate in fats.
3. Food sources: Consume a variety of foods from different sources of production. This will not only
reduce the exposure to a single pesticide but will also give a better mix of nutrients.
Naturally occurring compounds:
Silicon compounds
Silicon is an element possessing properties typical to metals and non-metals.
Uses of silicon:

Silicon plastic (silastic) is used for artificial skin grafts to protect healing skin.

Silica (sand) is the main ingredient used for making glass, cement, porcelain and glazes. It is also
found in human skeleton.

Silicon combines with oxygen to form silicones which are resistant to heat and moisture. Silicones
are widely used to coat kitchenware to make non-stick surfaces for oil free cooking.

Silicon is also used in the electronics industry to make semiconductors.
Limestone and marble
Limestone and marble are naturally occurring rocks. They are different forms of calcium carbonate.
There are several uses of these rocks. A few are given below:
1. White marble is used to make statues and monuments. Eg: The Taj Mahal is made of white marble.
2. Ground calcium carbonate is used as a coating pigment for paper because of its high brightness. It is
used in plastics because it imparts stiffness and strength. It is used in paints because it has high
brightness, and is weather resistant.
3. Limestone is used to make slaked lime which is used for white washing in buildings.
Paints
Paints are liquids which after application to the surface forms a solid film. They help to protect metallic
surfaces from corrosion, or to decorate the surface. Paints have three main components:
1. Pigments which add colour: Titanium oxide and zinc oxide are commonly used pigments. Zinc oxide
provides anti-corrosive coatings for various metals. Titanium oxide is replacing lead pigments which
were used earlier and are highly toxic.
2. Binders: The binders bind the pigments and make the paint more durable.
3. Solvents: These adjust the fluidity of the paints. Water is the solvent in water based paints while oil
based paints have solvents like alcohol or turpentine.
4. Gypsum and plaster of Paris (POP):Both gypsum and plaster of Paris are different forms of
calcium sulphate. When heated, gypsum changes to POP. This is used to make statues, chalks for
writing on black boards and casts for setting fractured bones in humans.
2
Organic compounds
The compounds present in living matter are called organic compounds. The main elements present in
organic compounds are carbon, hydrogen and oxygen. Nitrogen and sulphur may also be present.
Some important compounds are hydrocarbons, carbohydrates and proteins.
Carbohydrates
Carbohydrates are complex organic substances which form the bulk of your diet. They are the energy
suppliers in daily diet. The common carbohydrates are glucose, sucrose, lactose, fructose, cellulose and
starch.
Sucrose
Sugar
Lactose
Milk
Cellulose
Walls of plant cells
Starch
Potato, corn, rice, wheat
Proteins
Proteins are complex organic compounds containing nitrogen in addition to carbon, hydrogen and oxygen.
Proteins are another important constituent of your diet which is required for body building. Nuts, milk,
beans, chicken and pulses are rich in proteins. Almost all organs of the body contain a protein called
collagen which gives strength to the body.
Man-made materials
Materials that are not produced naturally but are created by humans using various methods are synthetic in
nature. Some examples of man-made materials are plastics, medicines, soaps and detergents, glass, etc.
Plastics: Small building blocks of the same or different kind when joined together they form a long
chain molecule of high molecular mass called a polymer. The process of forming these long chains of
molecules is called polymerization. Carbohydrates like starch and cellulose, proteins, jute, silk, cotton and
wool are all natural polymers.
Plastics are man-made polymers. They are not affected by acids or alkalis. Plastics degrade very
slowly and on burning produce harmful greenhouse gases.
Plastics are of two types:
1. Thermosetting plastics: These plastics can melt and take shape only once. After they have
solidified, they stay solid and cannot be melted and remoulded. For example,
 Melanine is used for making unbreakable cups, saucers and crockery.
 Formica is used for making smooth surface on table tops.
 Bakelite is used for making electrical plugs and switches.
2. Thermoplastics: These plastics can be melted and remoulded repeatedly. For example,
 Polyethylene or polythene is used to make carry bags for milk and water.
 Polyvinyl chloride (PVC) used to make raincoats, soles of shoes, water and gas pipes,
electrical wires, etc.
3


Polystyrene in the form of foam is commonly called thermocole and is used as packaging
material.
Nylon is used as a synthetic fibre
Cement
Cement is an important synthetic material used in the construction of buildings, dams, bridges and other
structures.
This cement can be used for various other purposes. Such as:
1. When mixed with sand and water it is used for plastering and to bind bricks and stones together.
2. When mixed with water, sand and gravel, forms a hard, solid mass called concrete. Concrete is used
to make sleepers in railway tracks and the framework for certain parts of the buildings. Steel rods
when embedded in wet concrete form reinforced concrete. This is much stronger than concrete and
forms the load bearing frame work in pillar construction for example, bridges
Bridge made out of reinforced cement
Glass
Glass is an amorphous (or non-crystalline) solid material which is a mixture of silica, soda and lime. It is not
a solid, gas or a liquid substance. Generally, it is classified as a rigid liquid, maintaining liquid properties
while acting like a solid. At very high temperatures, glass is melted into the liquid form and now can be
moulded into various forms. It can be easily recycled and can be used in several forms such as in making
window panes, electric bulbs, greenhouses, etc.
Greenhouse
Electric bulbs
Types of glass:
Glass is generally defined as a transparent, shiny substance that breaks very easily. You see several things
around you which are made of glass. For example, window panes, eyeglasses, etc. The type of glass used for
preparation of all these objects is different. There are many kinds of glass.
1.
Type of glass
Characteristic features
Uses
Commercial /
soda-lime glass
Most common commercial
glass, less expensive. Soft,
breaks and cracks easily. Not
resistant to high
temperatures.
Window panes, bottles
4
2.
Lead glass
(commonly
called Crystal)
Contains lead in addition.
Sparkles when cut.
3.
Pyrex glass /
Borosilicate
Resistant to heat and
chemicals. Can be shaped
and blown easily
4.
4.Optical glass
5.
Fibreglass
Consists of tiny glass fibres
which are loosely packed
together in a wool-like mass.
It can be used like wool or
cotton fibres to make glass
yarn, tape, cloth etc.
6.
Laminated
safety glass
Tough and strong and does
not develop cracks or shatter
like ordinary glass.
7.
Tempered
safety glass
Used in all-glass doors,
side and rear windows
of automobiles.
8.
Bullet proof
glass
It is a single piece of glass
that has been given special
heat treatment. It is several
times stronger than ordinary
glass. When it does break,
the whole piece of glass
collapses into small, dulledged fragments.
Thick, multilayer laminated
glass. This can stop bullets.
9.
Laboratory
glassware
It is made from heat resistant
glass to withstand rapid
change in temperature. It is
also more resistant to
chemical attack than
ordinary glass.
This type of glass darkens
when exposed to ultraviolet
rays and returns to their clear
state when the rays are
removed
Making beakers, flasks,
test tubes and special
chemical apparatus.
10. Photochromic
glass
Tableware. Radiation
shielding glass in
nuclear industry
because lead absorbs
harmful radiations.
For cooking and
serving utensils, lab
apparatus because it
can withstand high
temperatures.
Eyeglasses,
microscopes,
telescopes.
Electrical insulation,
chemical filtration.
Aeroplane wings and
bodies, automobile
bodies, curtain material
because it is fireresistant and washable.
Automobile
windshields
Security purposes
Used for windows,
sunglasses and
instrument controls.
5
Soaps and detergents
A soap is a salt of sodium or potassium with fatty acids like stearic, oleic and palmitic acid present in oils
and fats. Soaps are made from the breakdown of oils or fats by sodium or potassium hydroxide, they form
respective salts of fatty acids. This process is called saponification. Perfumes and colours are added to the
soaps before they are moulded and dried into cakes.
SOAPS
Hard soaps
Soft soaps
Contain sodium
Contain potassium
Uses: Shaving, washing clothes
Uses: As bath soaps
Detergents:
Detergents are made from petroleum products. Compared to soaps, they have better cleansing action and
form lather even in hard water unlike soaps. In hard water soaps form a white precipitate or scum which
sticks to the clothes giving it an unclean appearance and even results in wastage of soap.
However, unlike soaps, the biggest disadvantage of detergents is that they are non-biodegradable in nature
and they cause water pollution.
Medicines:
Medicines are chemicals used to treat a diseased condition without affecting the patient. Some medicines are
extracted from plants or animals but some others need to be made artificially from chemicals. There are
different type of medicines used for different purposes.
Type of medicine
Uses
Examples
1.
Antacids
For acidity
Milk of Magnesia
2.
Analgesics
Give relief from pain
Aspirin, Crocin
3.
Antipyretics
Bring down fever, reduce pain
Paracetamol
4.
Antiseptics
To prevent infection on cuts and wounds Dettol
5.
Antibiotics
Used to kill or prevent the growth of
Penicillin
disease causing microorganisms
6.
Anti-histamines
For allergies and hypersensitive
Benadryl
reactions and colds
***************************************************************************************
KSD
6