New Creative Science and Environment Book 7

1. What is magnet? What do you mean by magnetic induction?
Ü The substance which attracts small pieces of iron and always rests pointing

to the north and south direction when suspended freely is known as magnet.

Magnetic induction is a phenomenon by which a piece of magnetic material
becomes a magnet when brought near or in contact with the magnet.

2. Write any three differences between natural and artificial magnets.

SN. Natural magnets SN. Artificial magnets

1. the magnets that are found 1. Man-made magnets are called
in nature are called natural artificial magnets.
magnets.

2. They have irregular shape. 2. They have regular shape.

3. They have less attractive 3. They have more attractive
power. power.

F The substance which attracts small pieces of iron and always rests
pointing to the north and south direction is known as magnet.

F Following are the properties of magnet:

i) Magnet attracts magnetic substances.

ii) A freely suspended magnet comes at rest pointing to the north-south
directions.

iii) Like poles of a magnet repel and unlike poles attract.

iv) The magnetic force is greater at the ends than at in the middle.

v) Magnetic poles cannot be separated.
F The phenomenon by which a piece of magnetic material becomes a

magnet when brought near or in contact with a magnet is called magnetic
induction.
F Single touch, double touch and electric method are the methods of
making magnet.
F The magnet made by the use of electricity is known as electromagnet.

Mange tism 97

A. Fill in the blanks.

1. A freely suspended magnet rests showing ___________ and __________

direction.

2. Like poles always ___________ and unlike poles ____________.

3. Magnet produced by the use of electricity is called ______________.

4. ___________ magnets are made by human beings.

B. Match the following:

1. Magnetic force non-magnetic substance

2. Unlike poles greater at poles

3. Iron nail attract each other

4. Plastic magnetic substance

C. True or False?

1. Like poles of magnet always attract.

2. Magnetic poles cannot be separated.

3. Iron nail becomes a magnet when it is in contact with a magnet.

4. Iron is a non-magnetic substance.

D. Define the following terms.

1. Magnetic induction 2. Load stone

3. Natural magnet 4. Artificial magnet

E. Differentiate between:

1. Magnetic and non-magnetic substances.

2. Natural and artificial magnets.

3. Single touch method and double touch method

F. Answer the following questions.

1. What is magnet? Write its properties.

2. What do you mean by magnetic induction? Describe an experiment on

how iron nail gets magnetized when kept in contact with a magnet.

3. Describe double touch method of making magnet.

4. What is an electromagnet? How is it made?

5. Describe the single touch method of making magnet.

Wonderful - making surprise
to make something move toward or near
Attract - a soft wet mixture

Paste - ‰‰

98 New Creative Science and Environment; Book 7

10 Electricity

After the completion of this unit, students will be able to:
Æ define static and current electricity.
Æ separate conductors and insulators.
Æ draw an electric circuit.
Æ explain the application of electricity.

Electricity
Electricity is a form of energy produced due to the change in the number of

electrons in a body or the flow of electrons through a conductor.
There are two types of electricity on the basis of which they are produced.

They are:
i) Static electricity, and ii) Current electricity

i) Static electricity

The electricity produced due to the change in the number of electrons in a
nonconducting body is called static electricity. It is produced in the insulators
and cannot be transferred from one point to another. For instance, when we rub
a plastic pen on our head and bring near the pieces of paper, they get attracted
towards the pen. It is because static electricity is produced in the pen due to the
change in number of electrons during the process of rubbing.

To make a charged body Pen
Bits of paper
Rub your pen on your head and bring it
near the dust particles of your classroom. You Electricity 99
will find that the dust particles are attracted
towards the pen. It is because when the pen
is rubbed the number of electrons in the pen
gets changed and charge is developed. So, it
attracts the opposite charge of dust particles
towards it.

ii) Current electricity

The electricity produced due to the flow of electrons through a conductor is
called current electricity. It is a useful form of energy and can easily be changed into
other forms.

Electric charge

The electrical property of a particle is called electric charge.

An atom is electrically neutral due to Glass Silk thread
the equal number of protons and electrons. rod
But when the atoms gain or lose the electrons
in any way, then the charge is produced. If Ebonite rod
the electrons are gained by a body, it gains a
negative charge and if the electrons are lost
by the body then it bears a positive charge.

The similar charges repel and the
dissimilar charges attract to each other.

Memory Tip

Static electricity is the cause of lightening.

Question

# How is charge produced in a body?

Conductors and Insulators

The substances through which electricity can pass are called conductors and the
substances through which electricity cannot pass are called insulators. Metals like iron,
steel, nickel, cobalt, aluminum, copper, etc. are conductors and the substances
like paper, plastic, wood etc. are insulators.

Memory Tips

■ A human body is also a good conductor of an electric charge.

■ Electricity is the flow of charge in per unit time.
How to find out conductors and insulators?

Collect different materials like a coin, a cork, a rubber, a glass, a key, a pin,
a plastic scale, a sewing needle, paper, pencil lead, etc. Connect a cell, conducting
the wire, bulb and these materials as shown in the given figures.

100 New Creative Science and Environment; Book 7

Does the bulb glow in each case? What do you find? The bulb does not glow
with all the gives materials.

Some materials like coins, keys, sewing needles, pencils, lead, etc. allow
electricity to pass through them. These materials are called conductors.

Materials like corks, rubber, glass, plastic, scales, paper, etc. do not allow
electricity to pass through them. These materials are called insulators.

Electric circuit

Connect a bulb, a cell, a wire and a switch
as shown in the given diagram.

Such an arrangement is an example of a
circuit. An electric circuit is a complete path for
electricity to flow.

In an electric circuit, the direction of the
current is taken from the positive terminal to
the negative terminal of the cell as shown in the
above diagram.

The device which works with the use of electricity is known as a load. Bulbs,
electrical irons, etc. are called loads.

An electric switch checks the flow of electricity. When the switch is on,
electricity flows through the conducting wire and when the switch is turned off,
electricity cannot flow through the conducting wire.

Circuit diagram and circuit symbols

An electric circuit is the combination of a cell, a bulb, a conducting wire and
a switch. While drawing a circuit, it is very difficult to trace the actual diagram of
different elements of the circuit. So, we use the symbols instead of those elements.

Electricity 101

Some symbols used in an electric circuit diagram are as follows:

Closed circuit Closed circuit

If the switch is on, current flows through
the circuit. This is indicated by the glowing of the
bulb. Such kind of circuit is known as a closed
circuit.

Open circuit

If the switch is off, no current flows through
the circuit. The bulb does not glow here. This
kind of circuit is called an open circuit.

Short circuit Open circuit

If the negative and positive terminals of a battery are connected directly
then this condition is called short curcuiting. In this condition no current flows
through a bulb and the bulb cannot glow. Such kind of circuit is known as a short
circuit.

A short circuit may occur in our household circuits due to bad insulation
and cross connection. This may lead to fire damaging and destroying life as well
as property.

Use of electricity

With the development of different scientific technologies, the demand and
use of electricity is increasing. Some of the uses of electricity are as listed below.

102 New Creative Science and Environment; Book 7

i) To produce light
Electricity is used to produce light. Electric lamps convert electricity into

light energy. In filament lamps, tungsten wire is used to convert electricity into
light while in tube light mercury powder is used.

ii) To produce heat
Different heating devices are used to produce electrical energy to heat

energy. Such as electrical heaters, electric kettle, electric iron, etc.

iii) To run industries
Different industries such as cement industry, paper industry, carpet factory,

etc. use electricity for their operation.

iv) To run vehicles
There are different vehicles like safa tempos, electrical cars, bikes, etc. which

require electricity to work.

v) To use electronic devices
Electronic devices like radio, television, computer, etc. need electricity for

their work.

Combination cells bulb

There are two kinds of combination of cells.
They are :

(a) Series combination of cells: In this

combination the positive terminal of one

cell is connected to the negative terminal

of another cell. When we increase the

number of cells in series combination, the cells

voltage and brightness of the bulb (series combination of cells)

increases. cells

(b) Parallel combination of cells: In this

combination, all the positive terminals of the

cells are connected to one point and all the

negative terminals of the cells are connected

to another point. In this combination,

voltage and brightness do not increase as we

increase the number of cells. bulb

(Parallel combination of cells)

Electricity 103

How does lightning occur in the sky?

Clouds contain condensed and frozen water droplets. Frozen and larger
water droplets are present in the upper portion of the cloud. Similarly, smaller
lighter droplets are present in the lower portion of the clouds. Strong upward
and downward movements commonly occur in the cloud. Small water droplets
from the lower portion of the cloud are lifted to the higher portion during the
upward movement. Likewise the downward movement transports hail and ice
from the frozen upper portion to the lower portion of the cloud. When these hail
and ice collide with water droplets, water droplets freeze and release heat. This
heat keeps the surface of the hail and ice slightly warmer than its surrounding
environment. Thus, it forms a soft hail.

Negative cloud Positive cloud

When this soft hail collides with water droplets and ice particles, negatively
charged electrons are released from water droplets. Then, water droplets are
collected in lower portion of the cloud. As the process continues, a pool of
positive charge is formed in the upper portion and pool of negatively charge in
the lower portion of the cloud. When the electric field between the two opposite
charged regions is too high, lightning occurs. Lightning is a massive electrostatic
discharge. It occurs between clouds, within clouds and on the earth surface. It
causes a bright flash of light and a thunder. The tremendous energy which is
produced in this process heats the air in the path of the flow of electricity. Hence,
lightning is seen. Air cools rapidly as the energy dissipates. This expansion and
contraction of air produces a thunder.

How does lightning occur on the earth?

Clouds which form lightning have negative
charges on their lower surface. When clouds move
near to the ground surface, positive charges from the
ground get attracted by the negatively charged clouds.
Tall structures like mountains, communication towers,
buildings etc. help to produce positive charges above

104 New Creative Science and Environment; Book 7

the ground. It results is forming of electric fields and flow of electric current.
When electricity flows between these two opposite charged particles, lightning
occurs on the earth surface. So, the tall objects have great chance to get struck by
lightning than the shorter one.
Question to think

It is dangerous to rest under tall trees and communication posts during a
thunderstorm. Why?
Why is earthing done in buildings?

As we know, our homes and buildings
are at risk to lightning. So, to avoid the
damage due to lightning, metallic structures
(rods) usually made from copper is kept at
the top of the building. That rod is joined
with thick copper wire and buried inside
the earth surface. When the lightning strikes
the building, electric energy gets transferred
through the copper rod and wire to the
earth. In this way electric earthing saves the
building from damage. So earthing is done in buildings.

1. What is an electric circuit? Draw a diagram of a closed circuit.
Ü An electric circuit is a closed path through which current flows. A battery,

bulb, conducting wires and switch are essential for the construction of a
complete circuit.

2. It is dangerous to rest under a tall tree during a thunderstorm. Why?
Ü Tall trees, mountains, big buildings, electric and communication towers are

at risk during a thunder strom because lightning may pass through these
structures.

Electricity 105

3. Why does current not pass through an open circuit?
Ü Current connot jump from one end to another end of the open circuit. So, it

cannot pass in an open circuit.
4. Why is plastic an insulator?
Ü Current cannot pass through plastic. So it is an insulator.
5. What is current electricity?
Ü The electricity produced due to flow of electrons is called current electricity.

F The devices that produce electricity are called the sources of electricity.
F The substances through which electricity can pass easily are called

conductors, e.g. iron, copper, branches of trees, etc.
F The substances through which electricity cannot pass are called

insulators, e.g. plastic, rubber, glass, etc.
F An electric circuit is a closed path through which current flows.
F A battery, bulb, switch and conducting wires are essentials for the

construction of a circuit.
F The circuit in which the positive terminal of a battery is directly connected

to its negative terminal is known as a short circuit.
F If there is no break in a circuit, current can easily flow through it. This

kind of circuit is called a closed circuit.
F If there is a break in a circuit, current cannot flow through it. This kind

of circuit is called an open circuit.
F Lightning is a massive electrostatic discharge that causes a bright flash

of light and thunder.
F Tall structures are at greater risk of lightning.

A. Fill in the blanks.
1. The electricity produced due to friction is called ____________.
2. Opposite charges ____________ to each other.

106 New Creative Science and Environment; Book 7

3. In ____________ circuit the bulb does not glow.

4. ___________ converts kinetic energy into electrical energy.

5. ___________ is a closed path through which current flows.
B. Match the following:

1. ammeter
2. bulb
3. switch
4. cell

5. resistance
C. True or False?

1. Like charges always attract.
2. Series combination of cells increases voltage.
3. Pure water is a good conductor of electricity.
4. Lightning occurs between the earth and cloud only.
5. Rubber is a good conductor of electricity.
D. Define the following terms.
1. Combination of cells
2. Sources of electricity
3. Electric circuit
4. Short circuit
5. Earthing on the building
E. Differentiate between:
1. Series and parallel combination of cells.
2. Dry cell and simple cell.
3. Closed circuit and open circuit
4. Conductors and insulators
F. Answer the following questions.
1. What do you mean by a short circuit? What happens when there is a

short circuit?
2. Draw a diagram of:

a) Closed circuit

Electricity 107

b) Open circuit
c) Dry cell
3. Write any four uses of electricity.
4. What do you mean by an open circuit?
5. What are conductors? Give any five examples.
6. What are insulators? Write five examples of insulations.
7. Why is earthing done on a building?
8. How does lightning occur on the earth?
9. How does lightning occur in the sky?

Lightning - bright flash of light
Thunder - heavy sound

Photo - light ‰‰

108 New Creative Science and Environment; Book 7

11 Matter

After the completion of this unit, students will be able to:

Æ explain about elements and compounds.
Æ define physical and chemical changes.
Æ distinguish element and compounds, physical changes and

chemical changes.

Introduction

If we look at our surroundings, we see a large number of things of different
sizes, shapes, appearances and texture. Everything in this universe is made up of
material, which in scientific terms is called matter. The air we breathe, the food
we eat, the clothes we wear, the houses where we live in, the paper on which we
write, the ink with which we write, wood, steel, plants, animals, clouds, stars, etc,
are made up of matter. In fact everything in this universe is made up of matter.
All these things can be felt with the help of any one our five senses, i.e. sight,
touch, smell, hearing and taste.

Matter may be defined as anything that occupies space, possesses mass and the
presence of which can be felt by any one or more of our five senses.

For example, as mentioned above, air is a matter because though we cannot
see it yet its presence can be felt by the blowing wind. Further, the fact that air
has mass and occupies space, can be checked by filling a balloon with air and
weighing it.

It is important to note that heat, light, sound, electricity, magnetism, etc. are
not considered matter because they do not have mass and do not occupy space.

States of Matter

Any thing that has weight and can occupy space is called matter. There are
three states of matter:

i) solid ii) liquid iii) gas

The matters having a fixed shape and a fixed volume are called solids. They

have the greatest intermolecular force and the least intermolecular space, e.g. metal,

wood, stone, etc.

Matter 109

The matters having a fixed volume but no fixed shape are called liquids.
Their intermolecular force is less than that of solids and the intermolecular space
is greater than the solids, e.g. water, milk, petrol etc.

The matters having neither a fixed shape nor a fixed volume are called gases.
They have the least intermolecular force and the greatest intermolecular space,
e.g. water vapour, hydrogen, nitrogen, oxygen, etc. The matter can be easily
changed from one form to another. For example, when water (liquid) is heated,
it changes into vapour (gas) and when water is cooled, it changes into ice (solid).

Division of matters

Matter

Pure substance Impure substance

Element Mixture

Compound

Heterogeneous Homogenous
mixture mixture

Physical change and chemical change

The change in the physical properties of a matter like colour, odor, taste,
state, etc. is called the physical change, e.g. making of salt solution, changing
of water into vapour, etc. It is a temporary change which can be easily reversed
back.

The change in the physical as well as chemical properties of matter is called
chemical change, e.g. burning of wood, electrolysis of water, rusting of iron, etc.

Differences between physical change and chemical changes

Physical change Chemical change

1. The change takes place only in the 1. The change takes place both in

physical properties of the matter. physical and chemical properties

of the matter.

2. It can be easily reversed back. 2. It cannot be reversed back.

3. It is a temporary change. 3. It is a permanent change.

4. Change in energy is not seen. 4. Change in energy is seen.

Example: changing of water into ice Example: electrolysis of water

110 New Creative Science and Environment; Book 7

(i) Element

It is a kind of pure matter which can neither be made from any simpler
substances nor can be broken into any simpler substances.

There are 118 elements known to us, out of which 92 are natural and others
are synthesized in the laboratory. The elements are also found in the solid, liquid
and gaseous state at the room temperature and normal pressure. They are also
categorised as metals, non-metals and metalloids.

Atom

The smallest particle of an electron

element which takes part in chemical

combination without division is

called the atom. The atoms of the same nucleus

elements are identical in all respects Protons neutrons
and that of different elements are shell

different, e.g. the atoms of sodium are

similar to its all aspects but the atoms Structure of an atom
of sodium are different from that of

potassium.

Memory Tips

E. Rutherford discovered nucleus of an atom and he got the Nobel Prize in
Chemistry in 1908.

Compound

It is also a pure substance formed by the chemical combination of two or
more elements in a fixed proportion by their weight, e.g. sodium chloride, water,
magnesium sulphate, calcium carbonate etc.

There are 118 elements. But the compounds formed by them are thousands
in number. Although a compound consists of two or more elements as its
constituents, it is a pure substance, because it is formed by the chemical combination
of these elements and further it doesn’t have any properties of its constituents. To
form a compound, the elements should combine in a fixed proportion only. For
example to form H2O, hydrogen and oxygen should combine in the ratio of 1:8 by
their weight. Similarly, for making sodium chloride, sodium and chlorine should
combine in the ratio of 23:35 by their weights.

All the compounds are made up of their own molecules.

Matter 111

Molecules

Molecules are the smallest particles of a compound or an element which
exist independently.

A molecule of a substance shows all the properties of the compound. They
are held together by the chemical bonds. The molecules of an element are made
up of the atoms of the same element, e.g. a molecule of hydrogen is H2, a molecule
of chlorine is Cl2, and the molecule of oxygen is O2, etc.

Similarly, a molecule of a compound consists of atoms of more than two
elements, e.g. a molecule of water is H2O, a molecule of carbondioxide is CO2,
and a molecule of sodium chloride is NaCl, etc.

Differences between elements and compounds

Elements Compounds

i. Elements are the pure substances i. Compounds are the pure substances

having only one type of atoms. having two or more elements.

ii. It cannot be split into two or more ii. It can be split into two or more

simpler substances. simpler substances.

iii. Recently 118 elements have been iii. Thousands of compound have been

discovered. discovered.

iv. Hydrogen, oxygen, gold, silver, iv. Water, carbon dioxide, sodium

iron, etc. are the elements. chloride, ammonia, ozone are the

compounds.

Differences between atom and molecules

Atom Molecule

1. It is the smallest particle of an 1. It is the smallest particle of a

element that takes part in chemical compound that can exist freely in

reaction. nature.

2. It cannot be broken down. 2. It may be broken down into

respective atoms.

3. It is reactive. 3. It is usually stable.

Symbol
It is an abbreviation of the name of an element. It may be the first letter of

the name or first and any other letter of its English or Latin or Greek name.

Table of elements whose symbol is written by one letter.

S.N. Elements Symbol S.N. Elements Symbol
1. Fluorine F 6. Hydrogen H
2. Boron B 7. Phosphorus P

112 New Creative Science and Environment; Book 7

3. Carbon C 8. Sulphur S
I
4. Uranium U 9. Iodine N

5. Oxygen O 10. Nitrogen

Table of elements whose symbol is written by two letters

S.N. Elements Symbol S.N. Elements Symbol
1. Aluminum Al 8. Chromium Cr

2. Argon Ar 9. Cobalt Co
3. Beryllium Be 10. Chlorine Cl
4. Bismuth Bi 11. Magnesium Mg
5. Bromine Br 12. Cadmium Cd
6. Barium Ba 13. Radium Ra
7. Calcium Ca 14. Silicon Si

Table of elements whose symbol is written from Latin name

Elements (English name) Root name (Latin / German name) Symbol

Gold Aurum (Latin name) Au
Sodium Natrium (Latin name) Na
Potassium Kalium (Latin name) K
Iron Ferrum (Latin name) Fe
Copper Cuprum (Latin name) Cu
Silver Argentum (Latin name) Ag
Tungesten Wolfan (German name) W
Mercury Hydrargyrum (Latin name) Hg

The names of the first 20 elements with their number of protons, electrons
and neutrons, their atomic mass and their electronic configuration are tabulated
below:

S.N. Elements Symbol At. num At. mass

1. Hydrogen H 11

2. Helium He 2 4

3. Lithium Li 3 7

4. Beryllium Be 4 9

5. Boron B 5 11

6. Carbon C 6 12

7. Nitrogen N 7 14

8. Oxygen O 8 16

9. Fluorine Fe 9 19

10. Neon Ne 10 20

Matter 113

11. Sodium Na 11 23
12. Magnesium Mg 12 24
13. Aluminium Al 13 27
14. Silicon Si 14 28
15. Phosphorus P 15 31
16. Sulphur S 16 32
17. Cholorine Cl 17 35
18. Argon Ar 18 40
19. Potassium K 19 39
20. Calcium Ca 20 40

Molecular formula

The symbolic representation of the molecule of a substance is called its
molecular formula. It shows the total number of atoms present in that molecule,
e.g. a molecule of hydrogen is represented as H2, which means it consists of 2
atoms of hydrogen. Similarly, the molecule of sodium chloride is NaCl, which
means it consists of one atom of sodium and one atom of chlorine.

As stated earlier, H2 represents one molecule of hydrogen, which is stable
and can exist independently whereas, 2H represents the atoms of hydrogen,
which are very reactive and cannot exist independently.

Question

# What do you mean by 2N and N2?

Molecular formula of some compounds

S.N. Substances Molecular S.N. Substance Molecular
formulae formulae
1. Calcium carbonate 14. Nitrogen pentoxide
2. Nitric oxide CaCO3 15. Phosphorus pentoxide N2O5
3. Carbonic acid NO 16. Hydrochloric acid P2O5
4. Carbon dioxide 17. Hydrobromic acid HCl
5. Methane H2CO3 18. Nitric acid
6. Washing soda CO2 19. Sulphuric acid HBr
7. Baking soda CH4 20. Ammonia
8. Caustic potash 21. Phosphoric acid HNO3
9. Common salt Na2CO3 22. Gypsum salt H2SO4
10. Sulphur dioxide NaHCO3 23. Epsom salt NH3
H3PO4
KOH CaSO4
MgSO4
NaCl

SO2

114 New Creative Science and Environment; Book 7

11. Nitrogen dioxide NO2 24. Nitrogen trioxide N2O3

12. Nitrous oxide N2O 25. Quick lime CaO

13. Water, water H2O 26. Slaked lime, lime Ca(OH)2
vapour water

1. Why is silver an element?
Ü Silver is a pure substance as we cannot split it into two or more simpler

substances, and it has only one kind of atoms. They are the characteristics
of an element. So, silver in an element.

2. Write the molecular formulae of the following compounds.

Sodium chloride (common salt), hydrochloric acid, water, carbon dioxide
and silver chloride

Ü Molecular formulae of these compounds are mentioned below.

i) Sodium chloride = NaCl ii) Hydrochloric acid = HCl

iii) Water = H2O iv) Carbon dioxide = CO2
v) Silver chloride = AgCl

F Any thing that occupies space, has weight and that can be felt by the
senses is matter.

F An element is a pure substance that cannot be split into two or more
simpler forms and has a definite composition.

F An atom is the smallest particle of an element which may or may not
exist freely in nature but takes part in the chemical reaction.

F A compound is a pure substance made up of two or more elements
chemically combined in a fixed ratio by mass.

F A molecule is the smallest part of an element or a compound that can
exist freely in nature.

F The change in which no new substance is formed and exists temporarily
is known as the physical change, e.g. freezing of water.

F The change which exists permanently and in which other new substances
are formed is known as the chemical change, e.g. burning of wood.

Matter 115

1. Fill in the blanks.
a. ____________ is the lightest element.
b. Two or more elements are mixed in a definite ratio to form a ________.
c. Carbon dioxide is formed from the combination of ___________ and
____________.
d. Heat or light is either evolved or absorbed in a _________ change.
e. Heating of iron for pressing clothes is __________ change.

2. True or false?
a. Air is not a matter.
b. Atoms exist independently.
c. Molecular formula of sulphuric acid is H2SO4.
d. Compound is the combination of two or more elements in any
proportion.
e. Rusting of iron is a chemical change.
f. Melting of metal is a chemical change.

3. Match the following:

Column A Column B

Magnesium NH3
Zinc oxide Chemical change

Ammonia Element

Burning of wood Physical change

Mixing of salt and water ZnO
4. Define the following terms:
b. Compound
a. Matter d. Atom
c. Element f. Symbol
e. Molecules h. Chemical change
g. Physical change

116 New Creative Science and Environment; Book 7

5. Differentiate between:
a. Atoms and molecule
b. Compound and element
c. Chemical and physical change
d. H2 and 2H

6. Answer the following questions.
a. What is an element? Write the names of 5 elements that exist in nature.
b. What is compound? Name any five compounds.
c. Write the symbols of any 10 elements. Why is a symbol needed?
d. What do you mean by molecules? Name any 10 molecular formulae.
e. What do you mean by a physical change? Write its 3 characteristics.
f. What is a chemical change? Write down its 3 characteristics.

7. Distinguish whether the following changes are physical or chemical:
a. Burning of a paper
b. Combination of hydrogen and oxygen
c. Evolution of heat from the petrol on burning
d. Melting of iron
e. Heating of an iron ball
f. Magnetization of iron
g. Digestion of food
h. Switching an electric bulb

Compositions - something which is made of different parts
Temporarily - lasting for a short time
Reversible - that can be truned back
Permanently - lasting for a long time or for all time

‰‰

Matter 117

12 Mixture

After the completion of this unit, students will be able to:
Æ describe the types of mixtures.
Æ explain the separation of mixtures.
Æ describe evaporation, sublimation, centrifuging and

crystallization.
Æ identify the solution and its types.

Introduction

How do we judge whether the substances we buy from the market are pure
or not. All of you must have noticed the word ‘pure’ written on the packs of the
substances we buy. For a common person, pure means having no adulteration.
But, for a scientist, all of these things give actually mixture of different substances
and hence are not pure. For example, milk is actually a mixture of water, fat,
proteins etc. When a scientist says that something is pure, it means that all the
constituent particles of that substance are the same in their chemical nature. A
pure substance consists of a single type of particles.

As we see around, we see that most of the matters around us exist as
mixtures of two or more pure components.

Mixture is an impure substance formed by the physical combination of two
or more substances in any proportion by their weights.

The substances which form a mixture are called the components of the
mixture.

Types of mixture

According to the nature of particles of components, the mixtures are of two
types i.e. (i) Homogeneous mixture (ii) Heterogeneous mixture

The mixture in which the component particles are equally distributed and
cannot be seen through the naked eyes is called a homogeneous mixture, e.g.
sugar solution, salt solution, etc.

118 New Creative Science and Environment; Book 7

The mixture in which the component particles are not equally distributed
and they can be seen through the naked eyes, is called a heterogeneous mixture,
e.g.: mixture of mud and water, mixture of sand and water, etc.

Separation of mixture

Depending upon the nature and type of mixture, there are various methods
of separation of mixtures. The process of separation of mixture into its individual
component is called the separation of mixture.

The common separation techniques according to the type of mixture are

given below:

Types of mixture Method of separation of mixture
(1) Homogenous mixture

(a) Solid + Liquid Evaporation

Crystallization

Centrifuging

(b) Liquid + Liquid Distillation
Fractional Distillation
Chromatography

(2) Heterogeneous mixture Winnowing
(a) Solid + Solid Sieving

(b) Solid + Liquid Sedimentation & Decantation
Filtration

(c) Liquid + Liquid Using separating funnel

Evaporation
When we keep a common salt and water on a beaker and stir it for some time,

it gets dissolved. The mixture will be now clear and transparent. No substance
is seen in the mixture except water. Then how can we separate them? We can

Mixtur e 119

separate them by evaporation.
The process of changing the liquid into vapour on applying heat is known

as evaporation. The homogeneous mixtures which have different vapourisation
temperature can be separated by this process.

Objective
To separate a mixture of salt and water

Materials required
Beaker, salt solution, bunsen burner, wire gauge and tripod stand

Procedure

Salt solution

Salt

Evaporation

Æ Arrange the apparatus like wire gauge, tripod stand and burner as
shown in the figure.

Æ Take a beaker with salt solution.
Æ Heat the beaker till the water evaporates.

Observation and conclusion
A heap of the white substance remains at the bottom of the beaker.
The heap of the white substance is the salt that has been dissolved in

water to make a solution. Thus, it is concluded that vapourising temperature
of solute (salt) and solvent (water) is different. So water has evaporated out
and the salt is left in the beaker.

Sublimation

Usually when we heat any solid substance, first it changes into liquid then
to the gas but there are some certain solid substances that directly change into gas

120 New Creative Science and Environment; Book 7

when heat is supplied to them. They are iodine, ammonium chloride, camphor,
etc. If their vapour is cooled, it changes back into the solid state. This process is
known as sublimation.

Thus, sublimation can be defined as the process of converting solid directly
into vapour (gaseous form) on heating.

Objective

To separate a mixture of salt and camphor

Materials required

Cotton plug, porcelain basin, tripod stand, bunsen burner, mixture of
sand and camphor and a funnel

Procedure
Æ Take the mixture of
sand and camphor in
the porcelain basin and
cover the mixture with an
inverted funnel.
Æ Use wet and cold cotton
to plug the opening of the
funnel.
Æ Keep the apparatus as
shown in the figure and
heat it.

Observation and conclusion

From the mixture, camphor starts to vapourise and after some time, all
the camphor vapourises rapidly. When the heating is stopped and the camphor
is cooled, the vapour of camphor is condensed on the cooler part where we
have kept the cotton plug. The sand of the mixture is left in the basin.

Thus, the mixture of sand and camphor can be separated by using
sublimation.

Centrifuging

It is a process of separation of mixture with the help of centrifugal force.
Centrifugal force is the one which tends to move the body moving in a circular
path away from its centre.

Mixtur e 121

When a mixture of lighter and heavier particles is rotated with a high speed
then more centrifugal force acts on the heavier particles than the lighter particles.
Therefore heavier and lighter particles are separated in different levels.

The device in which centrifuging is done is called centrifuge or a centrifuging
machine. The mixture is poured into the test-tube of the centrifuge and allowed
to rotate at a very high speed either manually or by using electricity. After some
time, we will find the heavier particles settled at the bottom of the test-tube.

This process is used to separate cream from milk in dairies, blood cells from
plasma in the hospital laboratory, etc.

Memory Tip
The process of taking out of ghee from curd using madani is also an example

of centrifuging.

Question

# What type of mixture can be separated by centrifuging?

To separate chalk powder from water
Take a mixture of water and chalk powder in a
bottle with a tight lid. Then tie it with a strong thread.
Now rotate it in a high speed by holding the thread
at the one end. After some time, stop rotating and see
inside the bottle. You will find that the chalk powder
lies at the bottom of the bottle and the water lies above
it. Now you can slowly pour the water into another
vessel. In this way the mixture of chalk powder and
water can be separated.

122 New Creative Science and Environment; Book 7

Crystals

Crystals are the solids having a regular geometric shape and sharp edges.
The substances which can form crystals are called crystalline solids and the
substances which do not form crystals are called amorphous solids.

Different substances have the crystals of different sizes and shapes. For
example, the crystals of sodium chloride are cubic and that of copper sulphate
octahedral as shown in the figures.

A crystal of A crystal of alum A crystal of A crystal of sugar
copper sulphate sodium chloride

Crystallization

It is the process of separation of mixture by the formation of crystals from
the saturated solution of that substance.

It is a common method of separation of mixture in which the super-
saturated solution of a substance is allowed to cool and the crystals separate out
from their solution. The crystals thus obtained are in the purest form. They leave
the impurities behind in the solution.

This method is suitable only for the crystalline solid but we cannot apply
it for the amorphous solids. For example, separation of CuSO4, sodium chloride,
alum crystals from their solutions and the separation of alum from the solution
of rock salt.

Memory Note

Æ The solution which cannot dissolve more amount of solute at a given
temperature is called saturated solution.

Æ The saturated solution prepared at the higher temperature which gives
off the excess solute dissolved in it when cooled is called super saturated
solution.

Mixtur e 123

To find bigger and smaller crystals

Make a saturated solution of CuSO4 by dissolving the CuSO4 in water.
While making the saturated solution, the CuSO4 should be added continuously
by stirring. Now, filter the solution and heat the filtrate in a porcelain basin
until the small crystals are seen on the walls of the basin then cut off the heat
and allow it to cool. You will see the small crystals separating out from its
standard solution.

It should be noted that if the solution is allowed to cool fast, small sized
crystals are obtained and if the solution is cooled slowly then the bigger
crystals can be obtained.

To observe the crystals of copper sulphate

Make a hot saturated solution of copper sulphate in a beaker. Hang a
piece of thread with a knot inside the beaker containing saturated solution.

As the solution cools, crystal is formed at the tip of the thread. The
crystals become bigger and bigger but its shape remains the same. In this
way, bigger crystals of the different substances can be made.

This method can be used to separate pure crystals from a mixture of two
or more crystals.

Solution

Homogeneous mixtures make solutions. The particles in the solution cannot
be distinguished with naked eyes. In the mixture of sarbat, we add lemon juice
and sugar in water. The lemon juice and sugar get completely dissolved to form
a solution.

Thus, solution can be defined as a clear, homogenous mixture of two or
more substances possessing the properties of its components. Salt solution, sugar
solution, lemon solution, acid solution, basic solution, alcoholic solution are the
examples of a solution. Water is an universal solvent, so it is widely used to
prepare solutions.

Solute and solvents: The components of solution

A minimum of two substances are required to form a solution. One of the
substances gets dissolved and another substance acts as a dissolving medium.

124 New Creative Science and Environment; Book 7

Those substances that are soluble in excess of other substances uniformly are
called solutes. Those substances that dissolve the soluble substances are called
solvents. In salt solution, salt is the solute and water is the solvent. It can be
expressed as

Solution → Solute + Solvent
This solution is a homogeneous mixture of solute and solvent.

In some solutions, there may be more than one solutes like in Navajeevan
which we drink during dehydration. In Navajeevan, solutes like salt, sugar and
orange flavour are present. The solutes are present in less amount and the solvent
in large excess to dissolve the solutes. Solutes are usually solids and solvents are
liquids. In a solution of alcohol and water, alcohol is present in less amount than
water. So alcohol is a solute and water is a solvent.

Types of solutions

As we have already discussed in class VI, here we study in short in order
to recall them. We can find six types of solutions based on the states of their
components. They are:

1. Solution of solid and solid: brass (copper and zinc)
2. Solution of solid and gas: smoke
3. Solution of solid and liquid: sugar solution
4. Solution of liquid and liquid: alcohol in water
5. Solution of gas and liquid: soda water (carsbon dioxide + water)
6. Solution of gas and gas: air (oxygen + nitrogen + water vapours, etc.)

Dilute and concentrated solutions

Depending upon the quantity of solute dissolved in the given solvent the
solution may be dilute and concentrated.

The solution in which relatively a small amount of solute is present in a
definite volume of the solvent is known as a dilute solution.

The solution in which relatively a large amount of solute is present in a
definite volume of the solvent is known as a concentrated solution.

Mixtru e 125

(5 gm CuSO4 in 50 ml water) (20 gm CuSO4 in 50 ml water)
A B

Take 50 ml – 50ml of water in 2 beakers and add 5gm of copper sulphate
in one beaker and 20gm of copper sulphate in another beaker. Stir the mixture
with a glass rod to dissolve the copper sulphate in water. Which solution A or B
is concentrated and which one is dilute? Explain its reason.

The solution of copper sulphate in beaker B is more concentrated. Because
in the beaker B, more amount of solute is dissolved. While beaker A is dilute
solution because comparatively less (or 5 gm) copper sulphate is dissolved in the
same volume of water.

Thus, dilute and concentrated are the relative terms. So, they cannot be
always the same and true.

Unsaturated, saturated and super saturated solutions

Take a beaker containing water. Keep a little amount of common salt in that
water and stir the solution. Then the salt gets dissolved. Again keep little amount
of salt in the solution. The salt again gets dissolved in this solution. The solution
which can dissolve more amount of solute in it is called an unsaturated solution.

Again go on adding more and more common salt to that unsaturated
solution and stir the solution to dissolve and observe. After some time, a stage is
reached when no more salt can be dissolved further. Salt begins to settle down at
the bottom. It is clear that there is certain limit to the quantity of salt that can be
dissolved. At this stage, the solution cannot dissolve any more solute. Thus, the
solution at which no more amount of solute can be dissolved at that temperature,
is known as a saturated solution.

126 New Creative Science and Environment; Book 7

Again, add some water in the saturated solution you have prepared, then
add more salt and stir it. It dissolves the salt. This activity conclud that more
amount of solute can be dissolved if the amount of solvent is increased.

Heat the saturated solution you have obtained by using a tripod stand and
wire gauge in a bunsen burner. Then add a little amount of salt. The solution
dissolves it. Again add a little more salt and observe it. The solution again
dissolves it. Thus, the solution that can dissolve more amount of solute when the
temperature of the solution is increased is known as supersaturated solution.

When we cool down the hot supersaturated solution then the solute settles
down at the bottom of the beaker. Thus, it is clear that temperature is the main
factor that determines the saturation of a solution.

Unsaturated solution Saturated solution Supersaturated solution

1. What type of mixture is separated by centrifuging?
Ü The mixture of heavier and lighter particles can be separated by centrifuging

such as cream from milk, chalk powder from its mixture with water, etc.
2. How can you obtain bigger crystals in the crystallization process?
Ü We can obtain bigger crystals in the crystallization process by allowing the

supersaturated solution to cool slowly.
3. Which method do you use to separate pure salt from rock salt? Why?
Ü We use crystallization to separate pure salt in the form of crystals. In this

process the impurities are left behind in the solution.

Mixtur e 127

4. Why is water known as universal solvent?

Ü Water is usually in liquid state. Water can dissolve large amount of
substances that are present in this universe. So water is known as universal
solvent.

5. Differentiate between solute and solvent.

Ü Some of the differences between solute and solvent are as follows.

Solute Solvent

i. It is the soluble substance i. It is the substance which dissolves

that gets dissolved in other other substances in it.

substances.

ii. Solutes are usually solids. ii. Solvents are usually liquids.

iii. It is present in less quantity in a iii. It is present in large quantity in a

solution. solution.

6. What happens to the concentration of the solution when the solvent is
added to it?

Ü On adding the solvent in a solution, the solute present in the solution is
relatively less in comparison to the amount of solvent. Thus, the concentration
of the solution decreases on increasing the solvent.

F Mixture is an impure substance formed by the physical combination of
two or more substances in any proportion by their weights.

F There are two types of mixtures (i) Homogeneous and (ii) Heterogeneous.
F A solution is a homogeneous mixture of solute and soluent.
F We can separate heavy and light particles by rotating them fast. This

process is called a centrifugation or centrifuging method.
F Sublimation is the process of converting solids directly into its vapour on

heating.
F The machine in which centrifugation is done is called centrifuge.
F Crystals are the solids having regular geometric shapes and sharp edges.
F The process of separation of a mixture by forming crystals of a substance

is called crystallization.
F Big crystals are formed when the supersaturated solution is slowly cooled.
F A pure substance has only one type of crystals.

128 New Creative Science and Environment; Book 7

F Solutes are the substances that get dissolved in other substances.
F Solvents are the substances that dissolve other substances.
F Dilute solutions have relatively less amount of solutes in them.
F Concentrated solutions have relatively higher amount of solutes in them.
F More amount of solutes can be dissolved in unsaturated solutions.
F No more amount of solute can be dissolved in a saturated solution at that

temperature.
F More amount of solute can be dissolved in the given solvent when the

temperature of the solution is increased. This is a supersaturated solution.

1. Fill in the blanks with appropriate words.
a. __________ mixture of two or more substances is a solution.
b. __________ and __________ are mixed to form a brass.
c. Smoke in the air is the solution of ___________ and ___________.
d. ____________ and ________ forms a solution.
e. More amount of solute can be added in __________ solution.

2. True or false?

a. In nature, it is difficult to get a pure substance.

b. Lemon juice with water forms a heterogeneous mixture.

c. Carbon dioxide and water mix to form soda water.

d. Solvent gets dissolved in the solute.

e. Crystallization is the process of converting crystals into liquids.

3. Define the following terms:

(a) Evaporation (b) Sublimation

(c) Crystallization (d) Centrifugation

(e) Solute (f) Solvent

(g) Solution (h) Dilute and concentrated solutions

Mixtur e 129

4. Match the following:

Group A Group B

Salt and water crystallization

Pure salt from rock salt evaporation

Pure CuSO4 from its solution centifuging
Cream from milk crystallization

Less sweet sarbat crystallization

Alcohol and water saturation due to increase in temperature

Sand and saw dust dilute solution

Crystal of copper sulphate liquid and liquid solution

Super saturated heterogeneous mixture

5. Which method do you use to separate:

(a) Iodine and salt (b) Sugar and water

(c) Cream from milk (d) Copper sulphate and water

6. Draw a labelled diagram of :

(a) Crystallization

(b) Sublimation

7. Write the differences between:

(a) Evaporation and Sublimation

(b) Homogeneous and heterogeneous mixture

(c) Crystals and crystallization

(d) Dilute and concentrated solution

8. Write the use of:

(a) Centrifuging

(b) Chromatography

(c) Crystallization

9. Answer the following questions.

a. Define solution. Give its five examples.

b. Why can the components of solution not be seen with naked eyes?

c. How can we increase the concentration of the solution?

130 New Creative Science and Environment; Book 7

d. What do you mean by a saturated solution, unsaturated solution and
supersaturated solution?

e. What do you mean by crystals? Write the process of obtaining crystal.
Give three examples of solids which contain crystals.

f. How can we differentiate dilute and concentrated solution of lemon
juice by tasting?

g. How can we get big crystals from crystallization of copper sulphate?

h. What is a crystal? How can crystals be prepared?

i. What type of mixture is separated by centrifuging process?

j. One should know the properties of the components of mixture to
separate the mixture. Explain with example.

Centrifuge – a machine for separating small denser particles in a liquid
by rotation

Concentration – strength of solid, liquid, gas or solutions

Crystallization – process of making crystals

Navajeevan - mixture of salt, water and sugar

Dehydration - removing of water from something

Factor - one of several things

Liquor - strong alcoholic drink

Lather - a white mass of small bubbles

Mixtur e 131

13 Metals and non-Metas

After the completion of this unit, students will be able to:
Æ distinguish metals and non-metals
Æ explain the characteristics of metal, non-metals, metalloids

and alloys.
Æ explain some useful alloys and non-metals.

Introduction

More than 118 different elements have been discovered so far. Many of
them are found in nature whereas some of them have been made by artificial
methods and are called synthetic elements. Based on their physical and chemical
properties, they have been mainly classified into two categories, called metals
and non-metals. Among these 118 elements more than 92% are metals and rests
are non-metals and very few are metalloids. Most of the metals are occurring in
the form of scums whereas very few like gold, silver and platinum are present in
free form. After the complete study of these metals and non-metals, they used
for the benefit of human beings.

Metals

Metals are the elements which are electropositive in nature, malleable,
ductile and good conductors of heat and electricity.

Lithium (Li), Sodium (Na), Potassium (K), Magnesium (Mg), Calcium (Ca),
Gold (Au), Silver (Ag), Mercury (Hg), Nickel (Ni), Iron (Fe), Copper (Cu) etc. are
some of the examples of metals.
Characteristics of metals

i) Metals are electropositive in nature, i.e., they lose electrons.
ii) Metals are generally malleable, i.e., they can be beaten into thin sheets.
iii) Metals are generally ductile, i.e., they can be drawn into wires.
iv) Metals in pure state possess luster, i.e. they have shining surface.
v) Metals are generally hard. The hardness varies in different metals.
vi) Metals are good conductors of heat and electricity.

132 New Creative Science and Environment; Book 7

vii) Mostly, metals possess high melting points.
viii) Metals are sonorous, i.e., they produce sound on striking their surface.
ix) Mostly, they have high tensile strength.
x) Generally, metals have high density.
xi) Metals are solid at the room temperature except mercury, cesium and

gallium.

Non-metals

The elements which are electronegative in nature, non-conductor of heat
and electricity, non-malleable and non-ductile in nature and do not possess luster
are called non-metals.

Some examples of non-metals are Hydrogen (H), Oxygen (O), Nitrogen (N),
Chlorine(Cl), Phosphorus (P), Carbon (C), Bromine (Br), Sulphur (S), etc.

Characteristics of non-metals

i) Non-metals are electronegative in nature, i.e.; they gain electrons.

ii) They are non- malleable.

iii) They are non-ductile.

iv) They are generally bad conductors of heat and electricity except
graphite.

v) Non-metals do not possess any luster except iodine.

vi) They are soft and brittle, i.e., they break into pieces when hammered
except diamond.

vii) They are non-sonorous.

viii) Generally they have low melting and boiling points except boron,
graphite and diamond.

ix) Generally, they have low density.

x) They have low tensile strength.

xi) They may be solid, liquid and gas at the room temperature.

Comparison of physical and chemical properties of metals and non-metals

Property Metals Non-Metals

1. Lustre Metals have lustre and can also be Except iodine, non-metals do

polished. not have lustre and also cannot

be polished.

2. Hardness Metals (except sodium and Non-metals (except diamond)
potassium) are generally hard. are generally soft.

Metals and non-Metas 133

3. Malleability Metals are malleable (can be Non-metals are neither

and ductility hammered into thin sheets) and malleable nor ductile. They are

ductile (can be drawn into wires). actually brittle.

4. Conductivity Metals are good conductors of Non-metals (except graphite
heat and electricity. and gas carbon) are bad
conductors of heat and
electricity.

5. Melting Metals (except mercury, cesium Non-metals (except carbon and

points and and gallium) generally have high boron) have low melting and

boiling points melting and boiling points. boiling points.

6. Sonorosity Metals are sonorous (i.e., produce Non-metals are non-sonorous

sound when hit with a hard (i.e., do not produce any sound

object) when hit with a hard object.)

7. Density Metals generally have high Non-metals generally have low
density. density.

8. Tensile Metals generally have high tensile Non-metals generally have low
strength
strength and hence cannot be tensile strength and hence can

easily broken. be easily broken.

9. Physical state Metals are generally solid (except Non-metals (except bromine
mercury, cesium and gallium which is a liquid) are either
which are liquids at room solids or gases at room
temperature). temperature.

Metalloids

Besides metals and non-metals, there is a third category of elements which
show the properties of both metals and non-metals. These elements are called
metalloids. Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb) , tellurium
(Te), etc. are the examples of metalloids.

Memory Note

(i) Silver is the best conductor of heat and lead is the poorest conductor of heat.
The sequence of conductivity is given below

Ag > Cu > Au > Al > W > Hg

(ii) Tungsten (W) has highest melting point

Alloys
We know that iron is the most widely used metal. But it is not used in the

pure state. This is because iron is a very soft metal. It stretches easily. However,
if it is mixed with a small amount of carbon (0.05%), it becomes hard and strong.
This mixture is called steel. If instead of carbon, iron is mixed with nickel and

134 New Creative Science and Environment; Book 7

chromium, we get stainless steel. It is very hard and does not get rust. Thus, we
can conclude that the properties of any metal can be changed if it is mixed with
some other metals or non-metals. This mixture is called an alloy.

The homogeneous mixture of two or more metals or metals and non-metals is
called an alloy.

Why are alloys prepared?
Alloys are prepared to meet the given properties
i) To increase the hardness.
ii) To increase the tensile strength.
iii) To lower the melting point.
iv) To modify the chemical reactivity.
v) To reduce the electrical conductivity.
vi) To modify colour.
vii) To increase the resistance to corrosion.

Memory Note

An alloy which contains the mercury as one of the constituents is called
amalgams. For example zinc amalgam, sodium amalgam, etc.

Some common alloys and their composition

Alloy Composition Properties Uses
1. Steel
Iron (99.95%), Hard, tough and Construction of ships,
Carbon (0.05%)
strong bridges, vehicles, etc.

2. Stainless steel Iron (74%), Hard and does For making cutlery,
Chromium (18%), not rust utensils and surgical
Nickel (8%) instruments.
Malleable,
3. Brass Copper (80%), strong, resists For making utensils,
Zinc (20%) corrosion, can be screws, nuts and bolts
easily cast

4. Bronze Copper (90%), Very strong and For making statues,
5. Solder Tin (10%) highly resistant coins, medals, ship’s
to corrosion propeller, etc.
Lead (50%),
Tin (50%) Has a lower For joining electrical
melting point wires together.
than either lead
or tin

Metals and non-Metas 135

Some Useful Alloys and non-metals

Brass

Brass is an alloy formed from copper and
zinc. It is a non-corrosive and strong metal. Due
to the presence of copper, it has germicidal and
antimicrobial property. It is yellow in colour. It
is used in making statues, roof of temples etc. It
is also used as a decorative material like vase,
photo frames, gifts etc. Sacred instruments
for worshipping gods and goddesses like a
bell, dish, pots, etc. are made by using brass.
It is also used to make containers for keeping
clothes and other stuffs. Handles, locks and
keys in doors and windows are made by using
brass. It is also used in musical instruments like
tyamko, ghanta, etc.

Bronze

Bronze is also an alloy. It is the solid solution
of copper and tin. It is light yellow in colour. Due
to its low melting point, it can be easily moulded
into desirable shapes. Most of the kitchen utensils
are made from bronze. Dish, cups, bowls, etc. are
made from bronze. It is also used in rewarding
materials like gifts, decorative items, etc. It does
not corrode easily.

Sulphur

Sulphur is a non-metal. It does not dissolve
in water. It is mainly used as a gun-powder for
making bullets and ammunition. It is also used
in the paste for making match-sticks in match-
stick industries. The fire crackers which we use
in Deepawali and other special occasions contain
suphur. It is even used in different medicines.
Direct use and transport of sulphur in large
quantities without permission may be illegal. It
must be used with care.

136 New Creative Science and Environment; Book 7

Iodine

Iodine is an example of a non-
metal. It is used as a mineral. The
common salt that we use in our
daily life contains iodine. Lack of
iodine in our food causes a thyroid
disease called goiter. Iodine easily
vapourises at a low temperature.
So we must be aware about the loss
of iodine. A mixture of iodine and
alcohol is called tincture of iodine.
It is used to clean the wounds and
make the wound free of germs. Iodex, one of the commonly used medicines,
contains iodine in it. Iodex is used as a paste to get relief from pain in the body
parts.

1. How do metals occur in nature?
Ü Least reactive metals like gold and platinum are found in free states.

Moderately reactive metals are found in a combined state as oxides,
sulphides or carbonates. Highly reactive metals are never found in the free
state.

2. Give an example of metal which
i) is a liquid at the room temperature
ii) can be easily cut with a knife
iii) is the best conductor of heat.
iv) is the poorest conductor of heat

Ü i) Liquid metal is mercury (Hg)
ii) Alkali metals like Lithium (Li), Sodium (Na), Potassium (K), etc. can be
cut with a knife.
iii) Silver (Ag) is the best conductor of heat
iv) Lead (Pb) is the poorest conductor of heat.

3. Explain the meaning of malleable and ductile.
Ü Metals are malleable because they can be beaten into sheets. Silver and gold

are the most malleable metals. Metals are ductile because they can be drawn

Metals and non-Metas 137

into wires after heating. Gold and silver are best ductile metals. Gold is so
ductile that one gram of good can be drawn into a wire of about 2 kilometer.

4. Which metals do not corrode and why?

Ü Metals such as silver (Ag), gold (Au) and platinum (Pt) do not corrode
because they are less reactive.

5. State two ways to prevent the rusting of iron.
Ü Two methods used to prevent the rusting of iron are:

i) Galvanization
ii) Formation of alloy with nickel and chromium
6. Name three metals which are found in nature in a free state.
Ü Gold (Au), Silver (Ag) and Platinum (Pt) are the least reactive metals. Hence,
they occur in the nature in a free form.

A. True or false
1. Silver is the best conductor of heat and electricity.
2. Bromine is a liquid non-metal.
3. Brass is an example of a non-metal.
4. Antimony is an example of a metal.

B. Match the following.

Gold alloy

Arsenic non-metal

Bromine metalloid

Bronze metal

C. Define the following terms with examples.

1) Metals

2) Non-metals

3) Metalloids

D. Answer the following questions.

1. What is the meaning of malleable and ductile?

2. What are metalloids? Give any two examples.

3. Copper is used to make an electric wire. Why?

138 New Creative Science and Environment; Book 7

4. Write four differences between physical properties of metals and non-
metals.

5. What are alloys? Give any two examples.

6. Pure iron is not used to make utensils. Why?

7. What is meant by rusting?

8. What is meant by corrosion?
9. Metals are electropositive in nature. Why?
10. What are alloys? Why are they formed?
11. Metals are used to make cooking utensils. Why?
12. Define metalloids with two examples.
13. What do you mean by rusting of iron? How can we prevent it?

14. Silver, gold and platinum occur freely in nature. Why?

15. Write down three uses of each of :

a. Brass

b. Bronze

c. Sulphur

d. Iodine

Malleable - that can be converted into thin sheets
that can be converted into thin wires
Ductile - oxiginated compound

Rust - ‰‰

Metals and non-Metas 139

14 Some Useful Chemicals

After the completion of this unit, students will be able to:
Æ identify some useful chemicals.
Æ explain the characteristics and uses of phenol, dettol,

detergent, and chemical fertilizers.

We need different types of chemical substances in our daily life. These
different chemical substances have different uses. We use some chemical
substances in the form of foods and drinks as additives. These additives make
our food and drink tasty. Some chemicals are also used for cleansing purposes
like soap and detergents. Soap and detergents help to clean dirt and germs from
our body and clothes. Some chemical substances like Cetamol and Dettol are
used for medical purposes. Cetamol is used to control fever and Dettol is used to
make wounds and cuts free from germs. Some chemical substances are used as
chemical fertilizers for the growth and development of plants. Therefore, most
of the chemical substances have great use to mankind. The main sources of these
substances are plants and minerals. In this unit, we will study about some of the
important chemicals which we use in our daily life.

Phenol

Phenol is a useful chemical made from petroleum products.
It belongs to the alcohol group of organic compounds. Naturally,
it is colourless and have needle like crystals. After long time
storing these crystals become pink and finally reddish brown
in colour. Phenol is a soluble in organic solvents and slightly
soluble in water at the room temperature. Phenol was first
used for sterilizing wounds, surgical dressings, and surgical
instruments. Dilute solution of phenol is used to prevent
infections on wounds, to remove foul smell and kill flies. It is
also used as bactericides and insecticides. But its solid form
and concentrated solution is poisonous and scar the tissue. It
is widely used in industries for the manufacturing of resins,
plastics, insecticides, explosives, dyes, and detergents. It is also

140 New Creative Science and Environment; Book 7

a raw material for the production of medicinal drugs such as aspirin.

Dettol

Dettol is a disinfectant and antiseptic chemical
substance. In its concentrated form it is light yellow in
colour. It forms milky white emulsion with water. It is used
to clean cuts and wounds as it makes the wounds free from
germs. It also decreases the possibility of infection by micro
organisms like bacteria. Dettol is used in water for bathing
babies and washing clothes. It disinfects skin and clothes,
and hence makes us free from germs. Nowadays, we can
get Dettol soaps for bathing, liquid Dettol soap for washing
hands and face. Dettol avoids the wounds resulting from
pimples. The regular use of Dettol in bathing helps us to
get rid of most of the skin and communicable diseases.

Detergent

Detergent is a chemical substance that is used in the
removal of dirt or other foreign matters from contaminated
surfaces. It is also formed from petroleum products. It gets
dissolved in water more readily than the soap. It removes
dirt by acting on the surface of the cloth. So it is also called
surfactants. Detergent removes dust and dirt by dissolving
it in water rather than producing insoluble scum as that of
soap. Detergent is also enriched with smelly components
that make our clothes smell fresh. It also cleans clothes
better than soap. So, it is more popular than soap. The water containing detergent
harms the plants by disturbing its growth and development. The drain containing
detergent rich water also pollutes water bodies and destroys aquatic life. So it
must be used with care.

Chemical fertilizers

Soil contains different kinds of minerals.
These minerals are needed by the growing plants.
Cultivating same kind of crop again and again
decreases the amount of minerals present in the
soil. This decreases fertility of land. As a result of
this, production of food becomes less. Finally, it
leads the problem of malnutrition and starvation.
So, it is necessary to retain minerals in the soil.

Some Useful Ceh micals 141

Those water soluble chemical substances that help to increase the fertility of land
by retaining minerals in soil are called fertilizers. Fertilizers that are made from
organic matters like grass, dung, bones, and other decayed materials are called
manure or organic fertilizers. Those fertilizers that are synthesized chemically in
laboratories are called chemical fertilizers. Most of the chemical fertilizers are the
compounds of nitrogen, phosphorous and potassium. Nitrogen, phosphorous
and potassium are the vital nutrients for plants.

(a) Nitrogen is essential for the growth and development of the plants’
bodies. It is the major element present in all kinds of proteins. Deficiency
of nitrogen in plant results in yellowish of leaves, unhealthy flowering,
decrease in the size of fruit and seed, stunted growth and slow growth.
Fertilizers like NPK-fertilizer, urea, Diammonium phosphate (DAP),
Ammonium sulphate, Ammonium phosphate, Ammonium nitrate
etc. provide nitrogen to the soil.

(b) Phosphorous is also an important nutrient for growing plants. It helps in
photosynthesis and formation of flowers, fruits and seeds. It is essential
for proper growth of roots and plant bodies as a whole. Deficiency
of phosphorous in plants causes falling leaves, retarded growth and
unhealthy development of roots, fruit and seeds. Fertilizers like NPK-
fertilizer, Super phosphate, Ammonium phosphate, Diammonium
phosphate, Bone meal, etc. can retain the phosphorous content in the
soil.

(c) Potassium is another important plant nutrient. It is important for
photosynthesis, respiration and formation of cellulose. It also helps
to reduce water loss by leaves, increases resistance to diseases and
plays an important role in germination of seeds. Lack of potassium
results in high risk of diseases, yellowish of leaves, falling of leaves
and death of plants by frost or heat. Fertilizers like NPK-fertilizer,
Potassium chloride, Potassium nitrite, Potassium sulphate and ash
provide potassium to the soil.

Over use of chemical fertilizers affects not only plants and soil but also
water resources. The over use of chemical fertilizers can even cause permanent
loss of fertility of land.

Chemical substances must be used wisely. The overuse of synthesized
chemical substances have a negative impact on human health. It also causes
pollution in the environment.

142 New Creative Science and Environment; Book 7

List any ten chemical substances and write for what purpose they are used
in your home and surrounding area.

F We need different types of chemical substances in our daily life.
F Dilute solution of phenol is used to prevent infections in wounds, to

remove foul smell and kill flies.
F Dettol is used to clean cuts and wounds as it makes the wounds free from

germs and reduce the possibility of infection.
F Detergent is a chemical substance that is used in the removal of dirt or

other foreign matters from dirty surfaces.
F Those substances that help to increase the fertility of land by retaining

minerals in soil are called fertilizers.
F Fertilizers that are made from organic matters like grass, dung, bones,

and other decayed materials are called manure or organic fertilizers.
F Chemical fertilizers are synthesized in the laboratory.
F Nitrogen, Phosphorous and Potassium are the vital nutrients for plants.
F If chemical substances are used randomly, it harms human health and

pollutes the environment.

1. What is phenol and how is it made?
Ü Phenol is a cleaning chemical substance made from petroleum products.

2. What is Dettol and how is it made?
Ü Dettol is a disinfectant and antiseptic chemical substance. It is made from

petroleum products.

3. Define fertilizers and write down any three examples.
Ü Those water soluble chemical substances that help to increase the fertility of

land by retaining minerals in soil are called fertilizers. For examples; NPK-
fertilizer, Potassium chloride, Potassium nitrite, Potassium sulphate, etc.

Some Useflu Che micals 143

1. Fill in the blanks with appropriate words.
a. We need different ……………… in our daily life.
b. …………. is sprayed to remove a foul smell and kill flies.
c. Detergent is also called ………………………….. because they act on
the surface and clean dirt and dust.
d. ..................... fertilizers are also called synthetic fertilizers.
e. Nitrogen, Phosphorous and Potassium are found in …………………..
fertilizer.

2. Select the best alternative for the following:
a. Dettol is used for:
i. Killing flies
ii. Removing foul smell
iii. Cleaning wounds
b. ………….. is the best cleansing agent.
i. Soap
ii. Detergent
iii. Dettol
c. Which of the following provides phosphorous to the soil?
i. Bone meal
ii. Potassium chloride
iii. Urea
d. ………….. is necessary for the growth and development of the plant
body.
i. Nitrogen
ii. Potassium
iii. Phosphorous
e. …………………… destroys the fertility of soil?
i. Overuse of detergents
ii. Overuse of Dettol

144 New Creative Science and Environment; Book 7

iii. Overuse of chemical fertilizers
3. Answer the following questions.

a. What are chemical substances?
b. Why do we use chemical substances?
c. Name any four chemical substances with their uses.
d. What is phenol? Write any two uses of phenol.
e. What is Dettol? Give any two uses of Dettol.
f. What are detergents?
g. Why are detergents called surfactants?
h. What are fertilizers? Name any two types of fertilizers.
i. What is manure? Give two examples of manure.
j. What are chemical fertilizers? Give any two examples.
k. Name three vital plant nutrients.
l. Write down any two functions of Nitrogen, phosphorous and

potassium.
m. Name two chemical fertilizers of nitrogen, phosphorous and potassium.
4. Differentiate
a. Manure and chemical fertilizer
b. Detergent and soap
c. Dettol and phenol.

Crystals - the chemical substances which have definite shapes and sizes.

Insecticides - chemicals that kill insects

Micro organisms - very small organisms.

Communicable- the disease which transforms from one animal to another

Some Useflu Che micals 145

15 Living Beings

(A) Vertebrates

After the completion of this unit, students will be able to:

Æ define vertebrates.
Æ classify vertebrates according to their mode of life and body

features.
Æ differenciate between warm blooded and cold blooded animals.
Æ find out the characteristic features of vertebrates.

Introduction

We see different types of animals in our surrounding. The photographs of
animals can be seen in books, magazines, films, etc. They vary in shapes, sizes,
habitats and their body structures. Some animals may have vertebral columns or
backbones while some have not. On the basis of the vertebral columns, animals
are divided into invertebrates and vertebrates.

Those animals that do not have a backbone or a vertebral column are known
as invertebrates. Some of the examples of vertebrates are spiders, ants, butterflies,
prawns, sea cucumbers, starfish, hydras, earthworms, etc.

Vertebrates

Those animals that have a backbone or a vertebral column
are known as vertebrates. A vertebral column is not a single bone
but it is a group of many small bones extending from the neck to
the coccyx. Some of the examples of vertebrates are humans, cows,
buffaloes, hens, pigeons, monkeys, frogs, snakes, fish, etc.

Vertebrates are kept in the phylum chordata. So all the animals

belonging to vetebrates are also known as chordates. Structures

of vertebral columns vary from animals to animals but they are

composed of vetebral columns to give a shape and support to the

body. Fig. vertebral column

146 New Creative Science and Environment; Book 7