School Science Health & Physical Education 6

Activity

Collect ten different materials from your surroundings. Classify these materials into
magnetic or nonmagnetic substances.

Magnetic substances Non-magnetic substances

Types of magnet

Natural magnet

The naturally occurring black rock of magnetite that has magnetic properties is
called a natural magnet. The natural magnet is also called a lodestone. The
lodestone has an irregular shape and is weaker than the artificial magnet.
Therefore, it is not used in devices. A natural magnet is a permanent magnet
because it retains its magnetic property for a long time.

Fig.: lodestone

Artificial magnet

Aluminium, nickel and cobalt are mixed to form an alloy called alnico. Alnico
can be used to make permanent magnets because it retains magnetism for a long
time. These magnets are of different sizes and comparatively more powerful than
natural magnets. The magnets which are made by human beings are called

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artificial magnets. They may be a bar magnet, U-shaped magnet, horseshoe
magnet or circular magnet, etc.

bar magnet U-shaped magnet horseshoe magnet

Reason to remember

A horseshoe magnet is more powerful than a U-shape magnet of the same
size. Why?

A horseshoe magnet is more powerful than a U-shape magnet of the same size
because poles of a horseshoe magnet are closer than those of U-shaped magnet.

Magnetism

The properties shown by a magnet are called magnetism. For example, a magnet
has two poles, i.e. North Pole and South Pole. A magnet has a magnetic field
around it. A magnet attracts magnetic substances. A freely suspended magnet
rests in the north-south direction.

Magnetic poles

The region of a magnet where a

maximum amount of magnetic force

is concentrated is called a pole. A

magnet has two poles, i.e. North Pole

and South Pole. They are present near

the two the ends of the magnet.

Magnetic poles cannot be separated.

When a magnet is suspended freely Fig.: bar magnet which clearly shows the actual pole
with the help of a thread, it rests in the of the magnet

north-south direction of the earth. The

end of the magnet which faces geographical north of the earth is called the north

pole of the magnet. Similarly, the end of the magnet which faces the geographical

south of the earth is called the south pole of the magnet. Magnetic force flows

from the north pole of the magnet and enters the south pole.

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Reason to remember

A freely suspended magnet always rests in N-S direction. Why?
A freely suspended magnet always rests in N-S direction because it is affected
by the magnetic property of the earth that is aligned in the North-South
direction.

The total distance between two ends of the magnet is called the magnetic length.
But the magnetic poles are not at the extreme ends of the magnet. They are located
a little bit inside the extreme ends. The distance between two magnetic poles is
called the effective magnetic length.

Activity

Objective: To find the poles of the magnet.
Materials required: A bar magnet, a magnetic compass, white paper, thumb
pins, cardboard, etc.
Procedure: Put a white paper on the cardboard and keep a bar magnet at its
centre. Outline the bar magnet.
Put a magnetic compass at different positions around the ends of the bar magnet
and mark the ends a, b, and c as shown by the needle of the compass. Magnetic
compass and bar magnet are replaced from the paper and the points on the
paper are joined with free hand-drawn lines.
Observation: When the lines are sketched, they meet a little inside the outline
showing the ends of the bar magnet.
Conclusion: This activity shows that the poles of the magnet are near the ends
of the magnet not at the ends.

Fact file

Earth’s magnetic field is 1000 times weaker than that of a regular bar magnet.

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Reason to remember

Sometimes magnets attract each other and sometimes they repel each other.
Why?
Sometimes magnets attract each other and sometimes they push each other apart
because similar poles of the magnets repel each other and their different poles attract
each other.

unlike poles of magnet attracting like poles of a magnet repelling

Activity

Get two bar magnets. Point the north pole of one magnet to the south pole of
the other. What happens? Observe. Now, point the north pole of one magnet to
the north pole of another. Do you feel the repulsion? Discuss the findings with
your friends.

Reason to remember

Poles of a magnet cannot be separated. Why?
The poles of a magnet cannot be separated because even the smallest of its
particles are molecular magnets. Each molecule of a magnet has its north and
south pole.

Activity

Objective: To show that magnetic force is concentrated at the poles of a magnet.

Materials required: Iron dust, paper, bar magnet, etc.

Procedure: Take a bar magnet and put it on the table. Put a white paper over the
bar magnet. Spread iron dust over the paper. Shake the table slowly.

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Observation : More amount of iron dust will be collected at the ends of the bar
magnet.

Conclusion: It proves that magnetic force of a bar magnet is concentrated at the
poles.

Magnetic field

Have you noticed that a magnet can

pull iron dust from upto a certain

distance only? For example, if we

keep an iron nail closer to the

magnet, it gets attracted strongly.

Similarly, if we keep the iron nail a

bit far from the magnet, the force of

attraction decreases. If the iron nail

is far enough, it does not get Fig.: a bar magnetic and magnetic field around it
attracted. From the given activity, it

is clear that a magnet can show its

effects only upto a certain distance called its magnetic field. The space around a

magnet where the magnetic effects can be felt is called a magnetic field.

S.N Permanent magnet S.N Temporary magnet

1 The magnet that retains its 1 The magnet that retains its

magnetic property for a long magnetic power for a short

period of time is called a period of time is called a

permanent magnet. temporary magnet.

2 A permanent magnet is made 2 Temporary magnet is made

from an alloy of aluminium, from soft iron.

nickel, copper etc. Example: electromagnet

Example: lodestone

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Activity

Objective: To show the magnetic field of a bar magnet

Materials required: iron dust, a bar magnet, paper

Procedure: Take a bar magnet and put it on the table. Put a chart paper on the
table. Put a bar magnet in the middle of this chart paper. Sprinkle iron dust
over the chart paper. Shake the chart paper gently and slowly.

Observation: The bar magnet attracts iron dust upto a certain distance only
and the iron dust gets arranged in a particular pattern.

Conclusion: There is a limited region around the magnet where the magnetic
effects of a magnet on magnetic substances can be observed. This region is
called magnetic field.

Magnetisation

An iron nail in contact with a magnet also behaves like a magnet. This happens
due to magnetisation. Magnetisation can be developed in iron, nickel, cobalt, etc.
The process in which a magnetic substance changes into a permanent or temporary
magnet is called magnetisation. Artificial magnets are made by way of
magnetisation. Some of the popular methods of magnetisation are:

a) Stroking method b) Electric method

Fact file

Magnetic poles of the earth keep moving. North pole of the earth has a magnetic
south pole and vice versa.

Stroking method

When a magnet is rubbed against an iron bar, the iron bar changes into a magnet.
This is because the molecules of an iron bar rearrange themselves in a single
direction. There are two ways of rubbing a magnet against an iron bar. They are
single touch method and double touch method.

Single touch method

Take a permanent magnet and rub its particular pole against an iron bar multiple
times in a single direction. After some time, the iron bar begins to show the
magnetic property. This is called a single touch method for magnetisation.

The process of magnetisation in which a particular pole of a permanent magnet

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is rubbed against an iron bar in a single direction is called a single touch method.
If the north pole of the magnet is rubbed against the iron bar, the North Pole will
be formed at the first end and South Pole at another end as shown in the figure.

Reason to remember

Stroking method can change an iron bar into a magnet. How?
Stroking method can change an iron bar into a magnet because it forces
molecules of the iron bar to align in a single direction.

Activity

To make a magnet by using the single touch method
Put an iron bar horizontally on the table. Place the north pole of the bar magnet
over one end of the iron bar and start rubbing it. On reaching another end of the
iron bar, lift the bar magnet back at the starting point. Repeat the process
multiple times. Did the iron bar change into a magnet? Test it by placing an iron
nail close to it.

S bar magnet

N
NS

Double touch method
In this process, two permanent magnets are rubbed against an iron bar. The north
pole of one magnet and the south pole of another are brought to the middle part
of the iron bar. Then we need to rub the magnets on the bar away from its middle
part in two directions. On repeating this process multiple times, the iron bar
develops magnetic properties.

The process of magnetisation in which the opposite poles from two different
permanent magnets are rubbed against an iron bar in opposite directions is
called a double touch method. In this method, the south pole of the permanent
magnet produces north pole in the iron bar and north pole of the bar magnet
produces south pole in the iron bar as shown in the diagram.

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NS

SN

NS

Fact file

Cranes use huge electromagnets to pick up metal scraps.

Electric method
If a current is flowing in a wire, a magnetic field is produced around it. That
magnetic field can be stored in a soft iron core. The magnet made this way is an
electromagnet. The electromagnet is a temporary magnet. It loses its magnetic
property soon. The temporary magnet formed by passing a current in an insulated
coil around a soft iron core is called an electromagnet.

Method to make an electromagnet

Take a soft iron nail and insulated copper wire. Wind the insulated copper wire
around the nail. The complete structure is called a solenoid. Now, the solenoid is
connected with a powerful battery. When the switch is on, electricity flows
through the wire. The magnetic force gets collected in the iron. It is now called an
electromagnet. The iron nail becomes a magnet as long as the current flows in the
wire.

Fig.: making of the electromagnet

Properties of an electromagnet

a) An electromagnet is a temporary magnet.

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b) The strength of an electromagnet can be changed according to our
requirements.

c) It can be magnetised and demagnetised in a short period of time.
d) Factors affecting the strength of an electromagnet:
i. Nature of the core metal: A soft iron core collects a large amount of

magnetic force in it.
ii. The number of turns of wire: Insulated wire is wound around the soft

iron core in a single direction. If the number of turns of wire is higher, the
electromagnet becomes more powerful.
iii. Current: The greater the current flowing in the wire, the more is the
magnetic field strength.

Activity

Wind an insulated copper wire around a soft iron core and supply electricity
from a battery. Does it attract an iron nail nearby? What happens to the iron
nail when we cut off the electricity supply?

Fact file

The world’s most powerful magnets are located at New Mexico and Florida
State University.

Reason to remember

An artificial magnet is more widely used than a natural magnet. Why?
An artificial magnet is more widely used than a natural magnet because the
artificial magnet is more powerful than a natural magnet of the same size.
Besides that artificial magnets can be produced in desired shapes, sizes and
strengths.

Application of electromagnet

An electromagnet is widely used in different devices. For example:
a) An electromagnet is widely used in generators, electric motors and

transformers.

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b) It is used in headphones, loudspeaker, buzzers and electric bells.

c) Induction cookers, MRI machines and hard disks of the computer also use an
electromagnet for them to work.

generator headphone MRI machine

Summary

1. Substances which attract iron, cobalt, nickel, etc. and always rest in a north-
south direction when suspended freely are called magnets.

2. Substances that are attracted by a magnet are called magnetic substances.

3. Substances that are not attracted by the magnet are called non-magnetic
substances.

4. Naturally occurring black rocks of magnetite that have magnetic properties
are called natural magnets. Natural magnets are also called lodestones.

5. Magnets made by human beings are called artificial magnets.

6. Properties of magnets give rise to magnetism.

7. The regions of a magnet where maximum amounts of magnetic force are
concentrated are called poles.

8. The total distance between two ends of the magnet is called the magnetic
length.

9. The distance between two magnetic poles is called the effective magnetic
length.

10. The space around a magnet where the magnetic effects can be felt is called a
magnetic field.

11. The process in which a magnetic substance changes into a permanent or
temporary magnet is called magnetisation.

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12. The process of magnetisation in which a particular pole of a permanent
magnet is rubbed against an iron bar in a single direction is called a single
touch method of magnetisation.

13. The process of magnetisation in which the opposite poles from two different
permanent magnets are rubbed against an iron bar in opposite directions is
called a double touch method of magnetisation.

14. The temporary magnets made by passing an electric current in an insulated
coil wrapped around a soft iron core is called an electromagnet.

Exercise

1. Fill in the blanks with appropriate words.
a. The object that can attract iron, nickel, cobalt, etc. is called ……..

b. The properties shown by the magnet are called …………...

c. The substances that are not attracted by the magnet are called ………
substances.

d. Lodestone is a ……………. magnet.

e. The ……….. are the regions where the magnetic force is maximum.

2. Write True for the correct and False for the incorrect statements.
a. An iron rod buried under soil for a year can attract iron pins.

b. Like poles of magnets repel and their unlike poles attract
each other.

c. The magnetic force is concentrated in the middle part of a magnet.

d. Magnetism is gained when a magnet is hammered and heated.

e. An iron nail in contact with the magnet acts like a magnet and attracts
another iron nail.

3. Select the best answer from the given alternatives.
a. Which of the following is a magnetic substance?

i. Rubber ii. Plastic iii. Wood iv. Iron

b. Which of the following is not a magnetic substance?

i. Iron ii. Nickel iii. Cobalt iv. Zinc

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c. Which of the following is a natural magnet?

i. Bar magnet ii. U-shaped magnet

iii. Lodestone iv. Horse shoe magnet

d. Which is not the method of magnetization?

i. Heating ii. Single touch

iii. Double touch iv. Electrical

e. Which of the following uses electromagnet?

i. Electric bell ii. Dynamo

iii. Both 'i' and 'ii' iv. None of them

4. Match the following:

Magnetic compass i. repel each other

Like poles ii. temporary magnet

Unlike poles iii. natural magnet

Lodestone iv. attract each other

Electromagnet v. navigation

5. Write your answer to the following questions in a word each.
a. Which magnetic device helps in navigation?
b. Which mineral is a lodestone made of?
c. In which direction a freely suspended magnet rests?
d. What is the term for the actual distance between two magnetic poles?
e. Which alloy is used to make a permanent magnet?

6. Write any two differences between:
a. Magnetic substanes and non-magnetic substances

b. Natural magnet and artificial magnet

7. Give reasons:
a. Nickel is called a magnetic substance but gold is not.

b. Lodestone is called a natural permanent magnet.

c. A bar magnet is called an artificial permanent magnet.

d. A bar magnet collects more iron dust at poles.

e. A soft iron core is used to make an electromagnet.

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8. Draw the following diagrams:

a. bar magnet b. U-shaped magnet

c. horse-shoe magnet d. magnetic compass

9. Answer the following questions.
a. What is a magnet? List its properties.

b. Define magnetic force and magnetic field.

c. What is magnetism?

d. What are the magnetic poles? Define North Pole and South Pole.

e. Define magnetization. List the different methods of magnetization.

f. Describe the single touch method of making a magnet with the help of
a diagram.

g. Describe the double touch method of making a magnet with a diagram.

h. How can we make an electromagnet? List the properties of the
electromagnet.

i. Write down any three ways to increase the strength of an electromagnet.

10. Project work

a. Take an iron nail, about 4-inch long. Wrap an insulated copper wire
around the iron nail in a single direction. Connect one end of the wire to
the positive terminal and another to the negative terminal of a battery.
Now, bring some iron dust near the nail and observe. Does the iron nail
attract the iron dust? What is the reason behind this? Discuss this in the
class.

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8.2 Electricity

Topics in Their Order according to CDC Curriculum

1. Simple cells
2. Symbols used in electricity and drawing electric circuit
3. Simple methods to produce heat using electricity
4. General introduction to fuse and MCB

Learning outcomes

At the end of this unit, students will be able to:
1. Show they understand simple cells and how to make them.
2. Draw an electric circuit of conducting wire, switch, cell and resistance.
3. Produce heat with the help of dry cell, nichrome or constantan wire.
4. Discuss the functions of fuse wire and MCB.

Learning outcomes

Current electricity: The electricity produced by the flow of electrons in a
conductor is called current electricity.
Sources of electricity: The devices that produce electricity are called the sources
of electricity.
Cell: Cell is a device that converts chemical energy into electricity.
Simple cell: The primary cell that works by the ionization of dilute sulphuric
acid is called a simple cell.
Dry cell: The primary cell which contains paste of chemicals like ammonium
chloride, manganese dioxide, etc. is called a dry cell.
Electric circuit: The continuous conducting path in which electric current can
flow from source to the load is called electric circuit.
Source: The device that provides electricity in the circuit is called source.
Conducting wire: The metallic wire that allows electricity to pass from source
to the load is called conducting wire.

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Load: The device that converts electrical energy into other forms of energy is
called the load.

Open circuit: The electric circuit in which current does not flow is called an
open circuit.

Closed circuit: The electric circuit in which current flows from source to the
load continuously is called a closed circuit.

Heating effect: When electric current is passed through a high resistance wire,
it becomes very hot and produces heat. This is called heating effect of electric
current.

Electric heater: Electric heater is an electric device which converts electric
energy into heat energy.

Fuse: Fuse is a safety device that breaks an electric circuit during overflow and
short circuiting.

MCB: MCB is a circuit breaker which is used in place of a fuse to protect
overflow of current automatically.

Electricity

We see a variety of electrical devices in our daily life. Examples are an electric
bulb, computer, fan, heater, rice cooker, washing machine and electric iron. What
do we use to run these devices? Obviously, we use electricity. Electricity is the
most common and useful form of energy. It is produced due to the continuous
flow of electrons through a conductor. The electricity produced by the flow of
electrons in a conductor is called the current electricity. The SI unit of current
electricity is ampere (A).

Fact file

Electricity travels at the speed of light.

Uses of electricity

Electricity is a renewable source of energy. It is easy to use or convert into other
forms of energy. It is a major source of energy in the present world. Electricity is
used for lighting, heating, making magnets, etc.

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electric lamp rice cooker fan computer

Sources of electricity

Dry cells supply electricity to run a radio, clock, torchlight, etc. A bicycle dynamo
supplies electricity to run the bulb. Similarly, turbines produce electricity in
hydropower stations. Devices such as the dry cell, generator, dynamo and turbine
produce electricity. They are called sources of electricity. The devices that produce
electricity are called the sources of electricity.

dynamo generator photocell

Cell

A cell is usually a container with chemicals in it. When Fig.: cell
chemicals react in the cell, they produce electricity. Therefore,
the cell is a device that converts the chemical energy into an
electrical energy. A group of cells is called a battery. Some cells
can be recharged time and again. They are called rechargeable
cells, accumulators or secondary cells. The cells that cannot be
recharged are called primary cells. The primary cells can be
classified into simple cells and dry cells.

Simple cell

The primary cell that works by the ionisation of diluted sulphuric acid is called a
simple cell. It usually produces a very low amount (1.1 volts) of current. It is a
non-portable source of electricity. The simple cell is used in the science laboratory.

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Fig.: simple cell

The simple cell has a container filled with diluted sulphuric acid. We dip a copper
plate and a zinc plate in the acid. The copper plate works as a positive terminal
and zinc plate works as a negative terminal. A conducting wire connects these
two metal plates to the bulb. When chemical reactions start, the current flows in
the circuit and the bulb glows.

Fact file

Simple cells contain sulphuric acid. Hence, it is dangerous to transport these
cells. So simple cells are very rarely used.

Activity

To make a simple cell
Bring a beaker with diluted sulphuric acid. Dip a copper plate and a zinc plate
in it. Connect these plates with a LED bulb using a conducting wire. Now,
observe the bulb.

Dry cell

The primary cell which contains a paste of chemicals such as ammonium chloride,
manganese dioxide, etc. is called a dry cell. It is a portable source of electricity. It
usually produces 1.5 volts of current. It can be made in various shapes and sizes.
It is widely used in electronic devices such as a laptop, mobile, watch and
torchlight.

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Fig.: dry cell

Reason to remember

The dry cell is better than a simple cell. Why?
The dry cell is better than a simple cell because it is portable and produces more
emf than the simple cell.

Activity

To make a cell using fruits and vegetables
Bring a big potato, lemon, orange or apple. Dip a copper plate and a zinc plate
in it. Connect these plates with a LED bulb using a conducting wire. Now,
observe the bulb.

Electric circuit

Electricity needs a continuous conducting path to flow from the source to the
load. In this path, there are some basic components such as a conducting wire,
source, load and switch. Thus, the continuous conducting path in which electric
current can flow from the source to the load is called an electric circuit.

Fig.: wire, cell, bulb and switch

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Source

The device that provides electricity in the circuit is called a source. For example,
a cell, generator, dynamo, etc.

Activity

Use a copper wire, a dry cell, a LED bulb to make a closed circuit.

Conducting wire

Wires made from copper, aluminium, etc. are very good conductors of electricity.
These wires can be used to pass electricity in the circuit. Thus, the metallic wires
that allow electricity to pass from the source to the load are called conducting
wires.

Key (switch)

Key is a conducting piece of metal which is used to close or open the circuit. It is
also called a switch.

Load

The device that converts electrical energy into other forms of energy is called the
load. For example, bulb, computer, fan, refrigerator, mobile, etc.

SN Load SN Source

1. The device that converts 1. The device that provides electricity

electrical energy into other in the circuit is called source.

forms of energy is called the

load.

2. Load resists the flow of 2. Source promotes the flow of

electron. electron.

Example: electric heater Example: dry cell

Types of electric circuit

There are two types of electric circuit: open and closed.

Open circuit
In an open circuit, the electric current does not flow from the source to the load.

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In this condition, the load does not work. The electric circuit in which current
does not flow is called an open circuit.

Copper wire Switch
off
Dry cell
Bulb glowing

Fig.: open circuit

Reason to remember

Load does not work in an open circuit. Why?
Load does not work in an open circuit because, in it, electricity does not flow
from the source to the load.

Closed circuit
In the closed circuit, the electric current flows from the source to the load. In this
condition, the load works smoothly. The electric circuit in which the current
flows from the source to the load continuously is called a closed circuit.

Copper wire

Dry cell Switch
on

Bulb

Fig.: closed circuit

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Fact file

The first successful electric car was built in 1891 by America.

Symbols used for components in an electric circuit

An electric circuit is made up of several components. For example, a conducting
wire, source, load, switch, etc. These components are represented by certain
symbols. Among them, some common components and their symbols are given
below:

Electrical Symbol Function
Components
To connect components in an electric
Connecting wire circuit
To conduct electricity
Jointed wire Overlap of wires without joint
Wire crossing Source of electricity
One cell Source of electricity
Two cells Source of electricity
Many cells To produce light from electricity
Bulb To convert electrical energy into other
forms of energy
Resistor To make a circuit open

Open switch

Closed switch To make a circuit close

Ammeter A To measure electric current in a circuit
Voltmeter
Fuse V To measure voltage in a circuit

To protect a circuit from excessive
heating

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Fact file

1. The ammeter measures the amount of current flowing in an electric circuit.
2. A voltmeter measures the potential difference between any two points in an

electric circuit.
3. A galvanometer detects the presence of current.

Effects of current electricity

Current electricity can cause common effects such as heating, lighting, magnetism
and chemical reaction.

Heating effect

Some metals show a high resistance to electricity. For example, nichrome, constantan,
etc. When electricity is passed through a wire made of these metals, a large amount of
heat is produced. This effect of current electricity is called the heating effect. Thus, when
an electric current is passed through a high resistance wire, it becomes very hot
and produces heat. This is called the heating effect of electric current. The elements
that produce heat when electricity flows through them are called heating elements.

Characteristics of heating element

(i) It has a very high resistance. (ii) It has a very high melting point.

Reason to remember

Nichrome is used in an electric heater. Why?
Nichrome is used in an electric heater because it has a high resistance, high
melting point and does not burn when it comes in contact with the air.

Fact file

A common nichrome alloy is made from 80% nickel and 20% chromium.

Electronic devices

a. Electric heater
An electric heater is an electrical device. It contains nichrome wires which

convert the electrical energy into heat energy. We can see this heater being

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used for boiling water, cooking food and ironing clothes. Thus, an electric
heater is an electrical device which converts the electrical energy into heat
energy. Nichrome is a heating element. It has a very high resistance and
melting point. Therefore, it produces a large amount of heat energy without
melting.

iron rice-cooker electrict heater

b. Fuse

Sometimes more than a required amount of current flows in a circuit. This
causes overheating and burning of the electrical devices. It may also cause a
loss of life and property. Therefore, a safety device is used to break the circuit
in case the current overflows. This safety device is called a fuse. A fuse is
made from an alloy of lead and tin. Thus, a fuse is a safety device that breaks
an electric circuit during the current overflow and short circuiting.

A fuse has a very high resistance but a very low melting point. Once the fuse
breaks it should be replaced.

Fig.: varieties of fuse

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Reason to remember

Why is a fuse made of materials with a high resistance and low melting point?
Due to a very high resistance and low melting point of the materials used in a
fuse, the fuse melts and breaks the circuit in case of current overflow. This
prevents electrical devices from being damaged.

c. MCB (Miniature circuit breaker)
MCB is a safety device that breaks an electric circuit when there is an overflow

of current. It is sensitive to change in the amount of current. It breaks the
circuit automatically if there is an overflow of current. So, it is considered
better than a fuse.
MCB is a circuit breaker which is used in place of a fuse to automatically
prevent any overflow of current in the circuit.

Fig.: MCB

Reason to remember

An MCB is better than a fuse. Why?
A fuse melts during the overloading or short circuiting of current. It must be
replaced to use the circuit again. But MCB trips when there is a fault in the
circuit and current exceeds the safe limit. It can be reset after the fault has been
corrected. MCB is safer, easier and offers greater protection. So, we prefer MCB
to a fuse.

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Summary

1. Electricity produced by the flow of electrons in a conductor is called current
electricity. The SI unit of current electricity is ampere.

2. Devices that produce electricity are called the sources of electricity. For
example, a cell, photocell, generator dynamo, turbine, etc.

3. Cell is a device that converts chemical energy into electricity.
4. The primary cell that works by the ionisation of diluted sulphuric acid is

called a simple cell.
5. The primary cell which contains a paste of chemicals like ammonium chloride,

manganese dioxide, etc. is called a dry cell.
6. The continuous conducting path in which an electric current can flow from

the source to the load is called an electric circuit.
7. The device that provides electricity in the circuit is called the source.
8. An electric circuit in which the current does not flow is called an open circuit.
9. An electric circuit in which the current flows from the source to the load continuously

is called a closed circuit.
10. When an electric current is passed through a high resistance wire, it becomes

very hot and produces heat. This is called heating effect of electric current.
11. A fuse is a safety device that breaks an electric circuit during the current overflow and

short circuiting.
12. MCB is a circuit breaker which is used in place of a fuse to protect the overflow

of current automatically.

Exercise

1. Fill in the blanks with appropriate words.
a. Cell is a device that converts ………….. into electricity.

b. The electricity produced by the flow of electrons in a conductor is called

c. The basic components of an ………. are the source, conducting wire,
switch and load.

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d. The metallic wire that can pass electricity from source to load is called

e. The switch is used in an electric circuit to stop or allow the flow of ……..

2. Write True for the correct and False for the incorrect statements.
a. The SI unit of current is ampere.

b. The rechargeable cell is called primary cell.

c. The load does not work in a closed circuit.

d. The device that provides electricity in the circuit is called the source.

e. The electric circuit in which current does not flow is called an open
circuit.

3. Select the best answer from the given alternatives.

a. Which device detects a small amount of electricity?

i. ammeter ii. galvanometer iii. voltmeter iv. fuse

b. Which is a heating element?

i. aluminium ii. nichrome

iii. copper iv. both 'i' and 'ii'

c. Which is the source of heat energy?

i. electric heater ii. simple cell

iii. dry cell iv. all of the above

d. Which alloy is used to make a fuse?

i. lead and tin ii. copper and zinc

iii. nickel and chromium iv. all of the above

e. Which is a rechargeable cell?

i. simple cell ii. accumulator

iii. primary cell iv. none of them

4. Match the following: i. load
Cell ii. safety device
Reusable safety device iii. heating element
Fuse iv. MCB
Bulb v. converts chemical energy into electricity
Nichrome

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5. Write your answer to the following questions in a word each.
a. Which chemical ionizes in the simple cell to produce electricity?
b. Which chemical ionizes in the dry cell to produce electricity?
c. Which metal acts as a negative terminal in the simple cell?
d. What is the chemical composition of nichrome?

6. Write any two differences between:
a. Simple cell and dry cell
b. Open circuit and closed circuit
c. Fuse and MCB

7. Give reasons:
a. A simple cell is inconvenient to use in the electrical devices.
b. A dry cell is widely used in the electrical appliances.
c. Nichrome produces a large amount of heat energy.
d. A fuse is used in an electric circuit.
e. An MCB is better than a fuse.

8. Identify the following figures and write their uses.

9. Answer the following questions.
a. What is electricity? Write SI unit of current.
b. What are the sources of electricity? Give three examples.
c. Describe the structure of a simple cell with a labelled diagram.
d. What is an electric circuit? Draw an electric circuit connecting load,
source, key and bulb.
e. What is the heating effect of current electricity? Write its application.
f. Define heating elements with their characteristics.
g. What is a fuse? Write short note on MCB.

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10. Project Work

Collect four potatoes. Insert a zinc plate and a copper plate in each of the
potatoes. Use a copper wire to connect the zinc plate of one of the potatoes to
the copper plate of another. Connect copper plates of the first potato and zinc
plate of the last potato to the LED light. Does the bulb glow? What did you
just make? Discuss this in a group.

11. Glossary:
Ionization : breaking of a chemical compound into ions

Electrodes : rods that pass electricity

Alloy : homogeneous mixture of metals or metals and non-
metals

Domestic wiring : electric circuit made in house, school, industries, etc.

Short circuit : electric circuit where positive and negative terminals
are connected directly

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Unit Estimated Teaching Periods:

9 Matter Theory Practical
12 3

Topics in Their Order according to CDC Curriculum

1. Introduction to mixture and its types
2. Homogeneous and heterogeneous mixtures
3. Solution, colloid and suspension
4. Importance of solution
5. Methods of separation of mixture

Learning outcomes

At the end of this unit, students will be able to:
1. Define mixture and discuss its types.
2. Prepare solutions from substances used in our daily life.
3. Show they understand the methods to separate mixtures.
4. Show they understand evaporation.
5. Show they understand distillation.
6. Separate colours using paper chromatography.
7. Show they understand the use of centrifuge to separate mixture components.

Key terms of the unit

Matter: Matter is anything that has mass and occupies space.
Mixture: The mass obtained by mixing two or more substances in any proportion
without chemical change is called a mixture.
Homogeneous mixture: The mixture in which the mixing components are
distributed uniformly and they cannot be identified by naked eyes is called
homogeneous mixture.
Heterogeneous mixture: A mixture in which the components of mixture are
not distributed uniformly and they can be identified by naked eyes is called a
heterogeneous mixture.

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Solution: A solution is the homogeneous mixture of two or more substances.
or, an intimate mixture of solute and solvent is called a solution.

Solvent: The substance in which a solute dissolves is called a solvent.

Solute: The substance which gets dissolved in a solvent is called a solute.

Colloids: The heterogeneous mixtures which look like homogeneous with the
size of solute particles in between 10-7 to 10-5 cm in diameter are called colloids.

Suspension: The heterogeneous mixture in which the solute particles do not
dissolve but remain suspended throughout the medium is called suspension.

Evaporation: The changing of a liquid into vapours or gas is called evaporation.

Distillation: Distillation is the method that is used to separate liquids from solids
or from other liquids through vaporization (evaporation) and condensation.

Simple distillation: The distillation process which is used to separate a pure
substance from its mixture that dissolves another substance in it is called simple
distillation.

Paper chromatography: Paper chromatography is a process of separating the
coloured components of a mixture with the help of a paper which can adsorb
different substances at different rates.

Centrifugation: Centrifugation is the method of separating the mixture of
heavy particles and light particles by rotating the mixture at very high speed.
Centrifuge: Centrifugation is done by using a machine called centrifuge.

We see different substances in our surroundings. For example, water, air, food,
medicine, book, pen, pencil, etc. These are matters. Every matter may be different
in shape, size, colour, odour, taste and other features. But all matters share the
following two properties. They are:

i. Matters have a mass. ii. Matters occupy a space.

Heat, light, sound, shadow, etc. are not considered matters because they do not
have mass and do not occupy space. So, matter is anything that has a mass and
occupies a space. Every matter is made up of the smallest units called atoms or
molecules. Matters can be pure or impure. Pure matters are substances made up
of only one kind of atoms or molecules. Elements and compounds are pure
matters. Impure matters are substances made up of two or more kinds of atoms
or molecules. They include mixtures.

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9.1 Mixture

In our surroundings, many substances are impure. For example, atmosphere,
sandy water, smoke, alloy, food, milk, etc. In these substances, two or more
compounds or elements are mixed together. They are mixtures. Thus, the mass
obtained by mixing two or more substances in any proportion without a chemical
change is called a mixture. There are two types of mixture. They are:

i. Homogenous mixture

ii. Heterogeneous mixture

Reason to remember

Why are mixtures impure substances?
Mixtures are impure substances because they are made up of two or more
compounds or elements mixed in any ratio.

i. Homogenous mixture

In a homogeneous mixture, its components are uniformly distributed. Not all of
the components can be seen by our naked eyes. For example, a salt solution,
sugar solution, solution of copper sulphate, etc. Thus, the mixture in which the
mixing components are distributed uniformly and cannot be seen by our naked
eyes is called a homogeneous mixture.

Sugar Sugar
solution

Sugar

Water Salt solution(salty water) Dissolving of sugar in water

Fig.: salt solution, sugar solution in two different beakers

ii. Heterogeneous mixture

In a heterogeneous mixture, its components are not distributed uniformly. They
can be seen by our naked eyes. For example, sandy water, rice with husk, rice
with pebbles, etc. Thus, a mixture in which the components of the mixture are not
distributed uniformly and can be seen by naked eyes is called a heterogeneous
mixture.

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Fig.: sand with water in a beaker

Differences between homogeneous and heterogeneous mixtures

S.N. Homogeneous mixture S.N. Heterogeneous mixture

1. In a homogeneous mixture, the 1. In a heterogeneous mixture, the

components of the mixture are components of the mixture are

distributed uniformly. not distributed uniformly.

2. We cannot identify all the 2. We can identify all the

components of a homogeneous components of a heterogeneous

mixture. For example, salt mixture. For example, muddy

solution, brass, etc. water, pieces of stones in rice,

etc.

Salt + Water Salt solution (Homogeneous mixture)
Sand + Water Sandy water (Heterogeneous mixture)
Sugar + Water Sugar solution (Homogeneous mixture)
Dust + air Dusty air (Heterogeneous mixture)

Solution

Take a glass with some amount of water. Add a spoon of common salt in it. Stir
it with a spoon. The salt dissolves in water. This is now a salt solution. A solution

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is the homogeneous mixture of two or more substances. For example, a solution
of sugar and water, solution of salt and water, etc. We cannot see all the
components of the homogeneous mixture with naked eyes. A solution consists of
a solute and a solvent. Thus, an intimate mixture of a solute and a solvent is
called a solution.

Solution = Solute + Solvent

Solute and solvent

In a salt solution, the salt is a solute and water is a solvent. Similarly, in the
solution of copper sulphate and water, copper sulphate is a solute and water is a
solvent. Therefore, the substance in which a solute dissolves is called a solvent.
For example, water, alcohol, ether, etc. Similarly, the substance which gets
dissolved in a solvent is called a solute. For example, common salt, sugar, copper
sulphate, etc.

Reason to remember

Why is water called a universal solvent?
Water is called a universal solvent because it can dissolve most of the chemical
substances in it.

Differences between a solute and a solvent

S.N. Solute S.N. Solvent

1. Solute is a substance that gets 1. Solvent is a substance that

dissolved into another dissolves the solute.

substance.

2. Relatively, the amount of solute 2. Relatively, the amount of

in a solution is less than that of solvent in a solution is more

the solvent. Example: sugar in than that of the solute.

sugar solution. Example: water is a solvent in

sugar solution.

Uses of solution in our daily life

(i) Plants absorb salt and minerals in the form of a solution.
(ii) The food that we take is digested and absorbed in the form of solution.

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(iii) Aquatic plants and animals inhale oxygen in the form of water solution.

(iv) Most of the medicines, paints, ink, etc. are prepared and used in the form of
solution.

(v) We use some drinks in the form of solution.

Colloid

We know that sugar, salt, copper sulphate, etc. make a true solution in water. In
a solution, the size of solute particles is very small (10-7 cm or less in diameter).
These particles are invisible to the naked eyes or even a microscope. On the other
hand, there are some mixtures such as milk, blood, gum, fog, cloud, muddy water
and milk of magnesia which seem to be homogeneous but actually they are
heterogeneous. The size of solute particles in a colloidal solution is between 10-7
cm and 10-5 cm in diameter. Thus, the heterogeneous mixtures, which look like
homogeneous mixtures, with the size of solute particles between 10-7 cm and 10-5
cm in diameter are called colloids.

Since the colloidal solutions are heterogeneous in nature, the term ‘sol’ is used in
place of solution in order to distinguish them from a true solution. The solute
particles of the colloidal solution are called colloidal particles.

Characteristics of colloids

(i) Colloids are a type of heterogeneous mixture but look like homogenous
mixtures.

(ii) The size of colloidal particles is between 10-7 to 10-5 cm in diameter.

(iii) Colloidal particles cannot be separated by filtration as they pass through an
ordinary filter paper.

(iv) A colloidal solution is quite stable because colloidal particles do not settle
down when left undisturbed.

(v) Colloidal particles are invisible to the naked eyes. However, in some cases,
they are visible under an ultra-microscope.

Fact file

A colloidal solution of a liquid in a liquid is called an emulsion.

Suspension

Take some insoluble substances like chalk powder, wheat flour, lime, bleaching
powder, etc. Add these substances to water and stir the mixture. Now, we get a

226 Oasis School Science and Technology -6

heterogeneous mixture called a suspension. Thus, the heterogeneous mixture in
which the solute particles do not dissolve but remain suspended throughout the
medium is called a suspension.

In a suspension, the solute particles are bigger in size and heavier in weight. So,
they settle down easily when left undisturbed for some time. The diameter of the
solute particles in suspension is 10-5 cm or bigger. Due to their larger size, they
can be filtered easily by a filter paper.

Characteristics of a suspension

(i) A suspension is a heterogeneous mixture.

(ii) The size of solute particles in a suspension is 10-5 cm or more in diameter.

(iii) The solid particles in a suspension settle down easily when left undisturbed
for some time.

(iv) The solid particles of a suspension can be filtered by the filtration method.

(v) Suspensions are either opaque or translucent.

Methods of separation of components of mixtures

Substances which are mixed to form a mixture are called components of the
mixture. We need to separate these components to make them useful in our daily
life. Different components of a mixture have different physical properties such as
solubility, density and size. These differences in their physical properties help us
separate them from a mixture. Different methods are used to separate the
components of mixtures. In this unit, we will discuss evaporation, distillation,
chromatography and centrifugation.

Evaporation

Take some water in a porcelain basin and add common salt to make it a
concentrated solution. Heat the solution gently until all the water gets evaporated.
Finally, we are left with the common salt in the porcelain basin. This process is
called evaporation. So, the changing of a liquid into vapour or gas is called
evaporation.

Evaporation is a very common method to separate the solid and liquid components
of a homogeneous mixture. This process is based on the fact that liquids change
easily into vapour on heating whereas solids do not. The evaporation of a liquid
at room temperature is very slow. So, the process can be made quicker by heating
the solution.

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Fig.: evaporation

Distillation

Take a kettle and put some salt solution in it. Heat the solution gently. After some
time, vapour comes out of the sprout. With the help of a plate, convert this vapour
into liquid water. This process is called distillation. In distillation, we separate a
volatile liquid from a non-volatile solid or a mixture of two or more liquids
having different boiling points. Thus, distillation is the method that is used to
separate liquids from solids or from other liquids through vaporisation
(evaporation) and condensation. Mixtures like salt and water, iodine and alcohol,
potassium chloride and water, alcohol and water, etc. can be separated by way of
distillation.

Types of distillation

There are two types of distillation: simple and fractional.

Simple distillation
A distillation process used to separate a pure substance from another substance
in a mixture that it has dissolved in it is called a simple distillation.

Simple distillation is used to obtain a pure substance that dissolves another
substance. In this process, the solution is boiled and the vapour obtained is
condensed as a pure solvent. Simple distillation is used to obtain distilled water.
Similarly, the mixture of salt and water can be separated by this process. Simple
distillation is also used to separate a mixture of two miscible liquids having
widely different boiling points. For example, mixture of water (boiling point
1000C) and alcohol (boiling point 780C).

228 Oasis School Science and Technology -6

Activity

Objective: To separate pure water from a salt solution
Requirement: Round bottom flask, stand, Liebig’s condenser, collecting
vessel, clamp, burner, thermometer, wire gauze, tripod stand and salt
solution
Procedure: Take an RB flask of about 500 ml and pour about 200 ml of a salt
solution in the flask. Clamp the flask to the stand and place a wire gauze at
its base. Clamp the condenser with the delivery tube in another stand. Place
one end of the delivery tube inside the flask through a rubber cork and
another end to the collecting vessel. Put a thermometer in another hole in the
cork to maintain the temperature. Turn on the burner. Gradually, flow cold
water through one hole of the condenser after the solution is heated.
Observation: Vapour from the heated solution rises and passes to the
condenser through the delivery tube. Continuous inflow of cold water
through the condenser cools the vapour inside it. On cooling, the vapour
changes into water droplets that are collected in the vessel. After the
vaporisation completes, the salt is left in the bottom of the flask.
Result: Pure water and salt are separated from the mixture by using a simple
distillation process.

Fig. distillation

Conclusion: The simple distillation process can be used to separate
components of a mixture having different boiling points.

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Reason to remember

The mixture of the substances having almost the same boiling points cannot
be separated by way of distillation, Why?

Distillation is carried out by heating the mixture at a certain temperature. The
idea here is to collect the vapor from a particular liquid by heating it at a
particular temperature. If both components of the mixture have the same boiling
point, they will evaporate together and cannot be separated.

Use of distillation as a local technology

In some parts of Nepal, people make alcohol in Fig.: making alcohol at our home
their homes. They use the simple distillation
process. This is also called a local technology. To
make alcohol, they use fermented food and
water. The mixture of fermented food and water
is heated in a special heating device. After some
time, the vapours of alcohol and water come out
from the mixture. This vapour is converted to a
liquid called alcohol (raksi).

Chromatography

Chromatography is a modern technique for separation of a mixture. The word
chromatography has been derived from two Greek words 'kroma' and 'graphy'.
Here, kroma means colours and graphy means to write. So, different colours can
be separated from their mixtures by means of chromatography. Chromatography
was invented by the Russian botanist Tswett in 1906 AD to separate the coloured
pigments of plants. Nowadays, chromatography is widely used to separate
different types of mixture of solids, liquids and gases and even when small
quantities of substances are available. This technique is based on the principle of
selective adsorption of the components of the mixture. It means that different
substances move with different speed when they pass through a solid or liquid
medium. Depending on the nature of the moving and fixed phases,
chromatography is of three types. They are:

i. Paper chromatography

ii. Column chromatography

iii. Gas chromatography

230 Oasis School Science and Technology -6

In this unit, we will discuss only the paper chromatography.
Paper chromatography

Different coloured mixtures of red, blue, black, etc. can be separated by using the
paper chromatography technique. A filter paper can be used as a medium to
separate the colours in paper chromatography. Paper chromatography is a
process of separating the coloured components of a mixture with the help of a
paper which can adsorb different substances at different rates.

Reason to remember

A simple filter paper can be used to demonstrate paper chromatography,
Why?
A simple filter paper can be used to demonstrate paper chromatography
because a filter paper has a porous and fibrous structure. The components of a
mixture travel with different speed through the filter paper and get separated.

Activity

Objective: To separate coloured components of a black marker ink
Requirement: Filter paper, black marker, plate, distilled water in a dropper
Procedure: Take a circular filter paper or a white tissue paper. Mark a dark
point at the centre of the paper using a black marker. Put the paper in a plate.
Pour some drops of distilled water on the black spot at the centre of the filter
paper using a dropper and wait.

Observation: After about 30 minutes, you
will see different coloured rings on the filter
paper.

Result: The black ink of the marker is a
mixture of various colourful components.

Conclusion: Different coloured components
of a mixture pass with different speeds on
the filter paper. The coloured rings observed
on the filter paper show the components.

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Activity

Objective: To separate ink mixtures of different colours using a filter paper

Requirement: Filter paper, mixture of red and blue ink, pencil, beaker, distilled
water
Procedure: Take a beaker of volume 250 ml and pour about 50 ml of water in it.
Add about 3 drops of red ink and 3 drops of blue ink in the beaker. Cut a
rectangular piece of filter paper that should have a breadth of less than half of
the diameter of the beaker. Place a delivery tube or pencil horizontal on the
surface of the beaker. Clip or attach the piece of filter paper to the rod or delivery
tube so that a little portion of the filter paper should be under distilled water.
Leave the experiment for about 30 minutes.

Observation: We can see bands of blue and red ink
on the filter paper.

Result: Red and blue colours get separated from
their mixture.

Conclusion: The coloured components of a mixture
having different speeds in an adsorbing medium
can be separated on the same filter paper by using
paper chromatography.

Application of chromatography

1. Chromatography is used to separate various colours from their mixture.

2. It is used to separate and identify the medicines mixed in blood and urine.

3. It is used to separate the components of natural and artificial colours.

Centrifugation

Take a plastic bottle and prepare a mixture of sand and water. Tie the neck of the
bottle firmly with a strong string and rotate it gently for a while. After some time
the sand settles at the bottom of the bottle. From this activity it is clear that, a
mixture of heavy particles and light particles can be separated into the components
by rotating it at a very high speed. This process of separating a mixture by rotating
it at a high speed is called centrifugation. Thus, centrifugation is the method of
separating the mixture of heavy particles and light particles by rotating the
mixture at a very high speed.

232 Oasis School Science and Technology -6

Centrifuge

Centrifugation is done by using a machine called a centrifuge. In centrifugation,
the mixture of suspended particles in a liquid is taken in test tubes. The test tubes
are placed in a centrifuge and rotated rapidly for a while. As the mixture rotates,
heavier suspended particles settle down at the bottom of the test tubes and the
lighter particles or liquid remain on top. Now, the mixture can be separated by
way of decantation.

Uses of centrifugation

We can separate clay particles suspended in water, cream from milk, chalk
powder from water, sand and water, blood cells from plasma, etc. by using
centrifugation.

Fig.: centrifugation

Use of centrifuge as a local technology (churning)

Have you seen churning the curd to take out the cream? It is a local technology to
take the cream out of the milk. It works on the principle of centrifugation. In this
method, we collect curd in a wooden pot (theki). This curd is agitated with the
help of madani, a wooden stir. After some time, the cream comes out of the curd
and floats on the surface of the mixture.

Fig.: churning (mahipareko)

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Summary

1. Matter is anything that has a mass and occupies a space. For example,
atmosphere, sandy water, smoke, alloy, food, milk, etc.

2. The mass obtained by mixing two or more substances in any proportion
without a chemical change is called a mixture.

3. The mixture in which the mixing components are distributed uniformly and
cannot be identified by naked eyes is called a homogeneous mixture. For
example, a salt solution, sugar solution, solution of copper sulphate, etc.

4. A mixture in which its components are not distributed uniformly and can be
identified by naked eyes is called a heterogeneous mixture. For example,
sandy water, rice with husk, rice with pebbles, etc.

5. A solution is a homogeneous mixture of two or more substances. For example,
a solution of sugar and water,

6. The heterogeneous mixtures, which look like homogeneous mixtures, with
the size of solute particles between 10-7 to 10-5 cm in diameter are called
colloids. For example, milk, blood, gum, fog, cloud, muddy water, etc.

7. The heterogeneous mixture in which the solute particles do not dissolve but
remain suspended throughout the medium is called a suspension.

8. The changing of a liquid into vapour or gas is called evaporation.

9. Distillation is the method that is used to separate liquids from solids or from
other liquids through vaporisation (evaporation) and condensation.

10. The distillation process which is used to separate a pure substance from
another substance it has dissolved in the mixture is called a simple distillation.

11. Paper chromatography is a process of separating the coloured components of
a mixture with the help of a paper which can adsorb different substances at
different rates.

12. Centrifugation is the method of separating a mixture of heavy particles and
light particles by rotating the mixture at a very high speed.

13. Centrifugation is done by using a machine called centrifuge.

234 Oasis School Science and Technology -6

Exercise

1. Fill in the blanks with appropriate words.
a. The homogeneous mixture of solute and solvent is called………….

b. In........................mixture the mixing components do not distribute
uniformly.

c. The boiling point of alcohol is ......................... .

d. The size of solute particles in suspension is in between ………….. cm in
diameter.

e. Milk, blood, gum, fog, etc. are the examples of……………..

2. Choose the best answer from the given alternatives.

a. The mass obtained when two or more substances are brought together
in any proportion is called .........................

i. solution ii. Mixture

iii. element iv. compound

b. The mixture of salt and water is called ......................mixture.

i. homogeneous mixture ii. heterogeneous mixture

iii. same mixture iv. different mixture

c. The mixture of salt and water can be separated by...................

i. sedimentation ii. chromatography

iii. distillation iv. condensation

d. The boiling point of alcohol is....................

i. 78.5 0C ii. 100 0C iii. 58.70C iv. 87.50C

e. The mixture of red ink and blue ink can be separated by .........................

i. crystallization ii. filtration
iii. distillation iv. chromatography

3. Tick (√) the correct statement and cross (×) the incorrect one.
a. The components of a mixture do not lose their identity.

Oasis School Science and Technology -6 235

b. Milk is a colloidal solution.
c. In distillation, evaporation is followed by condensation.
d. The mixture of alcohol and water can be separated by paper

chromatography.
e. Centrifuge is used in centrifugation.
4. Identify the method of separating the components of the following
mixtures.
a. Salt and water
b. Water and alcohol
c. Red and green ink
d. Medicines mixed in urine
5. Differentiate between:
a. Homogeneous mixture and heterogeneous mixture
b. Centrifugation and chromatography
c. Evaporation and distillation
6. Write your answer to the following questions in a word each.
a. What kind of mixture is milk?
b. Which method of separation of mixture is useful to separate cream from

milk?
c. What is the size of particles in a solution?
d. Where do we use a centrifuge?
7. Give reasons:
a. Blood is a colloid.

b. A mixture of liquids having almost the same boiling point cannot be
separated by simple distillation.

c. Why is chromatography not able to separate components of
a solution which have the same speed?

236 Oasis School Science and Technology -6

8. Observe the given diagram and answer the following questions.
a. Which method of separation of mixture is shown in the diagram?

b. What kinds of mixture can be separated by this method?
9. Answer the following questions.

a. Define a mixture with any two examples.
b. What is a colloidal solution? Write down any three characteristics each

of a colloid and suspension.
c. List the major uses of a solution.
d. Describe the process of evaporation with the help of an example.
e. What is distillation? Write the names of some mixtures that can be

separated by this process.
f. What is chromatography? List its types. Describe paper chromatography

with its application.
g. What is centrifugation? Mention its application.

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10Unit Materials Used Estimated Teaching Periods:
in Daily Life
Theory Practical
8 2

Topics in Their Order according to CDC Curriculum

1. Chemicals used in daily life
i. Food materials (ghee, oil, salt, sugar and baking soda)
ii. Cleansing materials (soap, shampoo, detergents, phenol and stain remover)

2. Chemical pollution

3. Metals and non-metals

i. Physical properties of metals and non-metals (sonority, ductility, luster,
malleability, conductivity of heat and electricity and density)

Learning outcomes

At the end of this unit, students will be able to:
1. Give examples of chemicals used in daily life.
2. Differentiate between metals and non-metals based on their physical

properties.
3. Identify effects of chemical pollution owing to use of chemicals in daily life.

People use a variety of materials in their daily life. For example, salt, oil, ghee,
sugar, soap, shampoo, detergent, toothpaste and stain remover. Among them, some
are food materials and others are cleansing materials. In this unit, we will discuss
kitchen chemicals and cleansing chemicals.

Activity

Observe your home and surrounding areas. Identify different materials and
list them as shown in the given table.

In food items As cleanser, disinfectant, or sanitiser Others

Common salt, Soap, shampoo, …………….. Fertilizers, Tooth
……. paste, ….

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10.1 Some Useful Chemicals

Key terms of the unit

Baking soda: Baking soda is a white crystalline solid. Its chemical name is
sodium bicarbonate.
Common salt: Common salt is white crystalline solid. Its chemical name is
sodium chloride.
Sugar: Sugar is a white crystalline substance having sweet taste. Its chemical
name is sucrose.
Ghee: Ghee is a type of fat. It is obtained from the animal milk.
Vegetable oil: Vegetable oil comes from the seeds of plants.

Clanging agents: Those chemical substances that are used to remove dirt, dust,
stains, etc. from the surface are called clanging agents.
Disinfectants: Disinfectants are the chemicals used for killing germs.

In our daily life, we use chemicals for different purposes. They may have served
to enrich our food, boost agriculture, or support hospitals, etc. For example, we
use sugar for sweet taste, common salt for salty taste, lemon juice for sour flavor.
Likewise, soap, detergent, toilet cleaner, toothpaste, sanitizer, etc. are used for
cleaning.

1. Baking soda

Activity

Prepare some cupcakes using baking soda and without using it. Answer
these questions after your observation.

Which one is denser? Which one is puffy?

What is the role of baking soda in making the cupcakes?

Baking soda is a white crystalline solid. Its chemical name is sodium bicarbonate. It
is made of minerals. In cooking, baking soda is used to bloat food items such as
cakes, bread, cookies, biscuits, etc. Baking soda has many uses other than in
cooking. For example, it is used to produce carbon dioxide in a fire extinguisher;
develop medicines for hyperacidity and make soft drinks.

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Fig.: baking soda

Health impact of baking soda
An overdose of baking soda is harmful for health. It can cause nausea, vomiting,
feeling of being full, gas and bloating, stomach cramps, diarrhea, etc.
2. Common salt
Common salt is a white crystalline solid. Common salt dissolves in water. Its
chemical name is sodium chloride. It is also called a table salt or edible salt. It is
obtained naturally from sea water by using the process of evaporation. A rock
salt is obtained from underground deposits. Adding common salt to food gives
us a salty taste. Common salt is one of the major sources of sodium needed in our
body. It is also used as a food preservative to preserve fish, meat and pickles.

Fig.: common salt
Health impact of common salt
We need to add common salt in food at a proper amount. High consumption of
common salt can cause high blood pressure and mental stress.

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Fact file

Iodised salt is added to food for the prevention of iodine deficiency disorders.
Iodine deficiency in children causes goiter. It can also cause physical and mental
weakness.

3. Sugar

Sugar is a white crystalline substance having a Fig.: sugar
sweet taste. Its chemical name is sucrose. Sugar is
made from the sugarcane juice and sugar beet.
Some fruits such as banana, mango, pineapple,
etc. also contain a small amount of sugar. Human
blood has a small amount of sugar in it in the form
of glucose. Sugar is used to make soft drinks. It is
also used as a preservative in foods and beverages
because it prevents microbial growth.

4. Ghee

Ghee is a type of fat. It is obtained from animal Fig.: ghee
milk. It is in great demand for cooking and
medicinal purposes. Ghee is used to make a
variety of sweets and delicious food items. It is
also used as a moisturiser to prevent dry skin.
Excessive consumption of ghee results in the
accumulation of fatty substances in the body
tissues. This could lead to weight gain and other
health difficulties.

5. Vegetable oil

Vegetable oil comes from the seeds of plants. Seeds are crushed and pressed hard
to make oil. Oil is used to cook food items. Mustard oil, soybean oil, sunflower
oil, flaxseeds oil, olive oil, etc. are common examples of oil used by people.
Vegetable oil is also used to manufacture soap, vanaspati ghee (DALDA), etc.

sunflower seeds mustard seeds soyabean seeds

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Cleaning agents and disinfectants

Activity

Make a simple study of the different types of cleaning agents that are used in
your locality. Fill a table with the information in a format as shown below.

Cleaning Agent Use Feedback about the product

……………………. ………………… Good to remove dirt/stains/fat/………

Chemical substances used to remove dirt, dust, stains, etc. from surfaces are
called cleaning agents. Soap, shampoo, detergents, etc. are some examples of
commonly used cleaning agents.

i. Soap

Soap is a cleaning agent made from oil or fat. A variety of
soaps are made by adding different scented substances.
Soaps do not form lather in all kids of water.

ii. Detergent soap
detergent
Detergent is a synthetic powder or liquid chemical used stain remover
as a cleanging agent. Detergents are more soluble in water
than soaps. So, detergents are better as cleansing agents
than soaps.

iii. Stain remover

Sometimes, our clothes get stained. Such stains cannot be
removed by ordinary washing with soap or detergent. We
need stain removers to remove the dark stains from clothes,
carpets, beddings, etc. Thus, a stain remover is a chemical
used to clean unnecessary stains. Stain removers are available
in both powder as well as liquid forms.

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