NCERT Textbook - Chemical Effects of Electric Current Class 8 Notes | EduRev

NCERT Textbooks (Class 6 to Class 12)

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Class 8 : NCERT Textbook - Chemical Effects of Electric Current Class 8 Notes | EduRev

 Page 1


CHEMICAL EFFECTS OF ELECTRIC
CURRENT
CHEMICAL EFFECTS OF ELECTRIC
CURRENT
Y
our elders might have cautioned
you against touching an electrical
appliance with wet hands. But
do you know why it is dangerous to
touch an electrical appliance with wet
hands?
We have learnt earlier that the
materials, which allow electric current
to pass through them, are good
conductors of electricity. On the other
hand, materials, which do not allow
electric current to pass through them
easily, are poor conductors of electricity.
In Class VI, we made a tester
(Fig.14.1) to test whether a particular
material allows the electric current to
pass through it or not. Do you recall
how the tester helped us in deciding
that?
We found that metals such as copper
and aluminium conduct electricity
whereas materials such as rubber,
plastic and wood do not conduct
electricity. However, so far we have used
our tester to test materials which were
in solid state. But what about liquids?
Do liquids also conduct electricity? Let
us find out.
Paheli and Boojho want to
remind you that one
should not experiment
with the electric supply
from the mains or a
generator or an inverter.
Use only electric cells for
all the activities suggested
here.
Fig.14.1 : A tester
14.1 Do Liquids Conduct
Electricity?
To test whether a liquid allows electric
current to pass through it or not, we
can use the same tester (Fig. 14.1) which
© NCERT
not to be republished
Page 2


CHEMICAL EFFECTS OF ELECTRIC
CURRENT
CHEMICAL EFFECTS OF ELECTRIC
CURRENT
Y
our elders might have cautioned
you against touching an electrical
appliance with wet hands. But
do you know why it is dangerous to
touch an electrical appliance with wet
hands?
We have learnt earlier that the
materials, which allow electric current
to pass through them, are good
conductors of electricity. On the other
hand, materials, which do not allow
electric current to pass through them
easily, are poor conductors of electricity.
In Class VI, we made a tester
(Fig.14.1) to test whether a particular
material allows the electric current to
pass through it or not. Do you recall
how the tester helped us in deciding
that?
We found that metals such as copper
and aluminium conduct electricity
whereas materials such as rubber,
plastic and wood do not conduct
electricity. However, so far we have used
our tester to test materials which were
in solid state. But what about liquids?
Do liquids also conduct electricity? Let
us find out.
Paheli and Boojho want to
remind you that one
should not experiment
with the electric supply
from the mains or a
generator or an inverter.
Use only electric cells for
all the activities suggested
here.
Fig.14.1 : A tester
14.1 Do Liquids Conduct
Electricity?
To test whether a liquid allows electric
current to pass through it or not, we
can use the same tester (Fig. 14.1) which
© NCERT
not to be republished
we made in Class VI. However, replace
the cell by a battery. Also, before using
the tester we should check whether it is
working or not.
Activity 14.1
Join the free ends of the tester
together for a moment. This
completes the circuit of the tester
and the bulb should glow.  However,
if the bulb does not glow, it means
that the tester is not working. Can
you think of the possible reasons?
Is it possible that the connections
are loose? Or, the bulb is fused? Or,
your cells are used up? Check that
all the connections are tight. If they
are, then replace the bulb with
another bulb. Now test if the tester
is working or not. If it is still not
working then replace the cells with
fresh cells.
Now that our tester is working, let
us use it to test the various liquids.
(Caution: While checking your tester ,
do not join its free ends for more than
a few seconds. Otherwise the cells of
the battery will drain very quickly.)
Activity 14.2
Collect a few small plastic or rubber
caps of discarded bottles and clean
them. Pour one teaspoon of lemon
juice or vinegar in one cap. Bring
your tester over this cap and let the
ends of the tester dip into lemon juice
or vinegar as shown in Fig.14.2. Take
care that the ends are not more than
1 cm apart but at the same time do
not touch each other. Does the bulb
Fig. 14.2 : Testing conduction of electricity in
lemon juice or vinegar
of the tester glow? Does lemon juice
or vinegar conduct electricity? How
would you classify lemon juice or
vinegar— a good conductor or a poor
conductor?
When the liquid between the two
ends of the tester allows the electric
current to pass, the circuit of the tester
becomes complete. The current flows in
the circuit and the bulb glows. When
the liquid does not allow the electric
current to pass, the circuit of the tester
is not complete and the bulb does not
glow.
In some situations even though the
liquid is conducting, the bulb may not
glow. It may have happened in Activity
14.2. What can be the reason?
Do you remember why the bulb
glows when the electric current passes
through it? Due to the heating effect
of current, the filament of the bulb gets
heated to a high temperature and it
starts glowing. However, if the current
through a circuit is too weak, the
filament does not get heated
CHEMICAL EFFECTS OF ELECTRIC CURRENT 175
© NCERT
not to be republished
Page 3


CHEMICAL EFFECTS OF ELECTRIC
CURRENT
CHEMICAL EFFECTS OF ELECTRIC
CURRENT
Y
our elders might have cautioned
you against touching an electrical
appliance with wet hands. But
do you know why it is dangerous to
touch an electrical appliance with wet
hands?
We have learnt earlier that the
materials, which allow electric current
to pass through them, are good
conductors of electricity. On the other
hand, materials, which do not allow
electric current to pass through them
easily, are poor conductors of electricity.
In Class VI, we made a tester
(Fig.14.1) to test whether a particular
material allows the electric current to
pass through it or not. Do you recall
how the tester helped us in deciding
that?
We found that metals such as copper
and aluminium conduct electricity
whereas materials such as rubber,
plastic and wood do not conduct
electricity. However, so far we have used
our tester to test materials which were
in solid state. But what about liquids?
Do liquids also conduct electricity? Let
us find out.
Paheli and Boojho want to
remind you that one
should not experiment
with the electric supply
from the mains or a
generator or an inverter.
Use only electric cells for
all the activities suggested
here.
Fig.14.1 : A tester
14.1 Do Liquids Conduct
Electricity?
To test whether a liquid allows electric
current to pass through it or not, we
can use the same tester (Fig. 14.1) which
© NCERT
not to be republished
we made in Class VI. However, replace
the cell by a battery. Also, before using
the tester we should check whether it is
working or not.
Activity 14.1
Join the free ends of the tester
together for a moment. This
completes the circuit of the tester
and the bulb should glow.  However,
if the bulb does not glow, it means
that the tester is not working. Can
you think of the possible reasons?
Is it possible that the connections
are loose? Or, the bulb is fused? Or,
your cells are used up? Check that
all the connections are tight. If they
are, then replace the bulb with
another bulb. Now test if the tester
is working or not. If it is still not
working then replace the cells with
fresh cells.
Now that our tester is working, let
us use it to test the various liquids.
(Caution: While checking your tester ,
do not join its free ends for more than
a few seconds. Otherwise the cells of
the battery will drain very quickly.)
Activity 14.2
Collect a few small plastic or rubber
caps of discarded bottles and clean
them. Pour one teaspoon of lemon
juice or vinegar in one cap. Bring
your tester over this cap and let the
ends of the tester dip into lemon juice
or vinegar as shown in Fig.14.2. Take
care that the ends are not more than
1 cm apart but at the same time do
not touch each other. Does the bulb
Fig. 14.2 : Testing conduction of electricity in
lemon juice or vinegar
of the tester glow? Does lemon juice
or vinegar conduct electricity? How
would you classify lemon juice or
vinegar— a good conductor or a poor
conductor?
When the liquid between the two
ends of the tester allows the electric
current to pass, the circuit of the tester
becomes complete. The current flows in
the circuit and the bulb glows. When
the liquid does not allow the electric
current to pass, the circuit of the tester
is not complete and the bulb does not
glow.
In some situations even though the
liquid is conducting, the bulb may not
glow. It may have happened in Activity
14.2. What can be the reason?
Do you remember why the bulb
glows when the electric current passes
through it? Due to the heating effect
of current, the filament of the bulb gets
heated to a high temperature and it
starts glowing. However, if the current
through a circuit is too weak, the
filament does not get heated
CHEMICAL EFFECTS OF ELECTRIC CURRENT 175
© NCERT
not to be republished
SCIENCE 176
Activity 14.3
Take the tray from inside a discarded
matchbox. Wrap an electric wire a few
times around the tray. Place a small
compass needle inside it. Now
connect one free end of the wire to
the terminal of a battery. Leave the
other end free. Take another piece of
wire and connect it to the other
terminal of the battery (Fig. 14.4).
Fig 14.4 : Another tester
sufficiently and it does not glow. And
why is the current in the circuit weak?
Well, though a material may conduct
electricity, it may not conduct it as
easily as a metal. As a result, the
circuit of the tester may be complete
and yet the current through it may be
too weak to make the bulb glow. Can
we make another tester which can
detect a weak current?
You may use an LED (Fig. 14.3) in
place of the electric bulb in the tester
of Fig. 14.2. LED glows even when a
weak electric current flows through
it.
There are two wires (called leads)
attached to an LED. One lead is
slightly longer than the other.
Remember that while connecting to
a circuit, the longer lead is always
connected to the positive terminal of
the battery and the shorter lead is
connected to the negative terminal of
the battery.
Fig. 14.3 : LEDs
We can use another effect of an electric
current to make another kind of tester.
Do you recall that electric current
produces a magnetic effect? What
happens to a compass needle kept nearby
when current flows in a wire? Even if
the current is small, the deflection of the
magnetic needle can be seen. Can we
make a tester using the magnetic effect
of currents? Let us find out.
Join the free ends of two wires
momentarily. The compass needle
should show deflection. Your tester
with two free ends of the wire is ready.
Now repeat Activity 14.2 using this
tester. Do you find a deflection in the
compass needle the moment you dip
the free ends of the tester in lemon
juice?
Take out the ends of the tester
from the lemon juice, dip them in
water and then wipe them dry.
Repeat the activity with other liquids
such as tap water, vegetable oil, milk,
honey. (Remember to wash and wipe
dry the ends of tester after testing each
liquid). In each case observe whether
the magnetic needle shows deflection
or not. Record your observations in
Table 14.1.
© NCERT
not to be republished
Page 4


CHEMICAL EFFECTS OF ELECTRIC
CURRENT
CHEMICAL EFFECTS OF ELECTRIC
CURRENT
Y
our elders might have cautioned
you against touching an electrical
appliance with wet hands. But
do you know why it is dangerous to
touch an electrical appliance with wet
hands?
We have learnt earlier that the
materials, which allow electric current
to pass through them, are good
conductors of electricity. On the other
hand, materials, which do not allow
electric current to pass through them
easily, are poor conductors of electricity.
In Class VI, we made a tester
(Fig.14.1) to test whether a particular
material allows the electric current to
pass through it or not. Do you recall
how the tester helped us in deciding
that?
We found that metals such as copper
and aluminium conduct electricity
whereas materials such as rubber,
plastic and wood do not conduct
electricity. However, so far we have used
our tester to test materials which were
in solid state. But what about liquids?
Do liquids also conduct electricity? Let
us find out.
Paheli and Boojho want to
remind you that one
should not experiment
with the electric supply
from the mains or a
generator or an inverter.
Use only electric cells for
all the activities suggested
here.
Fig.14.1 : A tester
14.1 Do Liquids Conduct
Electricity?
To test whether a liquid allows electric
current to pass through it or not, we
can use the same tester (Fig. 14.1) which
© NCERT
not to be republished
we made in Class VI. However, replace
the cell by a battery. Also, before using
the tester we should check whether it is
working or not.
Activity 14.1
Join the free ends of the tester
together for a moment. This
completes the circuit of the tester
and the bulb should glow.  However,
if the bulb does not glow, it means
that the tester is not working. Can
you think of the possible reasons?
Is it possible that the connections
are loose? Or, the bulb is fused? Or,
your cells are used up? Check that
all the connections are tight. If they
are, then replace the bulb with
another bulb. Now test if the tester
is working or not. If it is still not
working then replace the cells with
fresh cells.
Now that our tester is working, let
us use it to test the various liquids.
(Caution: While checking your tester ,
do not join its free ends for more than
a few seconds. Otherwise the cells of
the battery will drain very quickly.)
Activity 14.2
Collect a few small plastic or rubber
caps of discarded bottles and clean
them. Pour one teaspoon of lemon
juice or vinegar in one cap. Bring
your tester over this cap and let the
ends of the tester dip into lemon juice
or vinegar as shown in Fig.14.2. Take
care that the ends are not more than
1 cm apart but at the same time do
not touch each other. Does the bulb
Fig. 14.2 : Testing conduction of electricity in
lemon juice or vinegar
of the tester glow? Does lemon juice
or vinegar conduct electricity? How
would you classify lemon juice or
vinegar— a good conductor or a poor
conductor?
When the liquid between the two
ends of the tester allows the electric
current to pass, the circuit of the tester
becomes complete. The current flows in
the circuit and the bulb glows. When
the liquid does not allow the electric
current to pass, the circuit of the tester
is not complete and the bulb does not
glow.
In some situations even though the
liquid is conducting, the bulb may not
glow. It may have happened in Activity
14.2. What can be the reason?
Do you remember why the bulb
glows when the electric current passes
through it? Due to the heating effect
of current, the filament of the bulb gets
heated to a high temperature and it
starts glowing. However, if the current
through a circuit is too weak, the
filament does not get heated
CHEMICAL EFFECTS OF ELECTRIC CURRENT 175
© NCERT
not to be republished
SCIENCE 176
Activity 14.3
Take the tray from inside a discarded
matchbox. Wrap an electric wire a few
times around the tray. Place a small
compass needle inside it. Now
connect one free end of the wire to
the terminal of a battery. Leave the
other end free. Take another piece of
wire and connect it to the other
terminal of the battery (Fig. 14.4).
Fig 14.4 : Another tester
sufficiently and it does not glow. And
why is the current in the circuit weak?
Well, though a material may conduct
electricity, it may not conduct it as
easily as a metal. As a result, the
circuit of the tester may be complete
and yet the current through it may be
too weak to make the bulb glow. Can
we make another tester which can
detect a weak current?
You may use an LED (Fig. 14.3) in
place of the electric bulb in the tester
of Fig. 14.2. LED glows even when a
weak electric current flows through
it.
There are two wires (called leads)
attached to an LED. One lead is
slightly longer than the other.
Remember that while connecting to
a circuit, the longer lead is always
connected to the positive terminal of
the battery and the shorter lead is
connected to the negative terminal of
the battery.
Fig. 14.3 : LEDs
We can use another effect of an electric
current to make another kind of tester.
Do you recall that electric current
produces a magnetic effect? What
happens to a compass needle kept nearby
when current flows in a wire? Even if
the current is small, the deflection of the
magnetic needle can be seen. Can we
make a tester using the magnetic effect
of currents? Let us find out.
Join the free ends of two wires
momentarily. The compass needle
should show deflection. Your tester
with two free ends of the wire is ready.
Now repeat Activity 14.2 using this
tester. Do you find a deflection in the
compass needle the moment you dip
the free ends of the tester in lemon
juice?
Take out the ends of the tester
from the lemon juice, dip them in
water and then wipe them dry.
Repeat the activity with other liquids
such as tap water, vegetable oil, milk,
honey. (Remember to wash and wipe
dry the ends of tester after testing each
liquid). In each case observe whether
the magnetic needle shows deflection
or not. Record your observations in
Table 14.1.
© NCERT
not to be republished
CHEMICAL EFFECTS OF ELECTRIC CURRENT 177
Table 14.1 : Good/Poor Conducting Liquids
S.No Material Compass Needle Shows Good Conductor/
Deflection Yes/No Poor Conductor
1. Lemon juice Yes Good Conductor
2. Vinegar
3. Tap Water
4. Vegetable oil
5. Milk
6. Honey
7.
8.
9.
10.
When the free ends of the
tester do not touch each
other, there is an air gap
between them. Paheli knows
that air is a poor conductor of
electricity. But she has also read
that during lightning, an electric
current passes through air. She
wonders if air is indeed a poor
conductor under all conditions.
This makes Boojho ask whether
other materials classified as
poor conductors also allow
electricity to pass under
certain conditions.
From Table 14.1, we find that some
liquids are good conductors of electricity
and some are poor conductors.
Actually, under certain conditions
most materials can conduct. That is why
it is preferable to classify materials as
good conductors and poor conductors
instead of classifying as conductors and
insulators.
We have tested the conduction of
electricity through tap water. Let us now
test the conduction of electricity through
distilled water.
Activity 14.4
Take about two teaspoonfuls of
distilled water in a clean and dry
plastic or rubber cap of a bottle. (You
may obtain distilled water from your
school science lab. You may also get
distilled water from a medical store
or a doctor or a nurse). Use the tester
to test whether distilled water
conducts electricity or not. What do
you find? Does distilled water
conduct electricity? Now dissolve a
pinch of common salt in distilled
water. Again test. What do you
conclude this time?
When salt is dissolved in distilled
water, we obtain salt solution. This is a
conductor of electricity.
The water that we get from sources
such as taps, hand pumps, wells and
ponds is not pure. It may contain several
© NCERT
not to be republished
Page 5


CHEMICAL EFFECTS OF ELECTRIC
CURRENT
CHEMICAL EFFECTS OF ELECTRIC
CURRENT
Y
our elders might have cautioned
you against touching an electrical
appliance with wet hands. But
do you know why it is dangerous to
touch an electrical appliance with wet
hands?
We have learnt earlier that the
materials, which allow electric current
to pass through them, are good
conductors of electricity. On the other
hand, materials, which do not allow
electric current to pass through them
easily, are poor conductors of electricity.
In Class VI, we made a tester
(Fig.14.1) to test whether a particular
material allows the electric current to
pass through it or not. Do you recall
how the tester helped us in deciding
that?
We found that metals such as copper
and aluminium conduct electricity
whereas materials such as rubber,
plastic and wood do not conduct
electricity. However, so far we have used
our tester to test materials which were
in solid state. But what about liquids?
Do liquids also conduct electricity? Let
us find out.
Paheli and Boojho want to
remind you that one
should not experiment
with the electric supply
from the mains or a
generator or an inverter.
Use only electric cells for
all the activities suggested
here.
Fig.14.1 : A tester
14.1 Do Liquids Conduct
Electricity?
To test whether a liquid allows electric
current to pass through it or not, we
can use the same tester (Fig. 14.1) which
© NCERT
not to be republished
we made in Class VI. However, replace
the cell by a battery. Also, before using
the tester we should check whether it is
working or not.
Activity 14.1
Join the free ends of the tester
together for a moment. This
completes the circuit of the tester
and the bulb should glow.  However,
if the bulb does not glow, it means
that the tester is not working. Can
you think of the possible reasons?
Is it possible that the connections
are loose? Or, the bulb is fused? Or,
your cells are used up? Check that
all the connections are tight. If they
are, then replace the bulb with
another bulb. Now test if the tester
is working or not. If it is still not
working then replace the cells with
fresh cells.
Now that our tester is working, let
us use it to test the various liquids.
(Caution: While checking your tester ,
do not join its free ends for more than
a few seconds. Otherwise the cells of
the battery will drain very quickly.)
Activity 14.2
Collect a few small plastic or rubber
caps of discarded bottles and clean
them. Pour one teaspoon of lemon
juice or vinegar in one cap. Bring
your tester over this cap and let the
ends of the tester dip into lemon juice
or vinegar as shown in Fig.14.2. Take
care that the ends are not more than
1 cm apart but at the same time do
not touch each other. Does the bulb
Fig. 14.2 : Testing conduction of electricity in
lemon juice or vinegar
of the tester glow? Does lemon juice
or vinegar conduct electricity? How
would you classify lemon juice or
vinegar— a good conductor or a poor
conductor?
When the liquid between the two
ends of the tester allows the electric
current to pass, the circuit of the tester
becomes complete. The current flows in
the circuit and the bulb glows. When
the liquid does not allow the electric
current to pass, the circuit of the tester
is not complete and the bulb does not
glow.
In some situations even though the
liquid is conducting, the bulb may not
glow. It may have happened in Activity
14.2. What can be the reason?
Do you remember why the bulb
glows when the electric current passes
through it? Due to the heating effect
of current, the filament of the bulb gets
heated to a high temperature and it
starts glowing. However, if the current
through a circuit is too weak, the
filament does not get heated
CHEMICAL EFFECTS OF ELECTRIC CURRENT 175
© NCERT
not to be republished
SCIENCE 176
Activity 14.3
Take the tray from inside a discarded
matchbox. Wrap an electric wire a few
times around the tray. Place a small
compass needle inside it. Now
connect one free end of the wire to
the terminal of a battery. Leave the
other end free. Take another piece of
wire and connect it to the other
terminal of the battery (Fig. 14.4).
Fig 14.4 : Another tester
sufficiently and it does not glow. And
why is the current in the circuit weak?
Well, though a material may conduct
electricity, it may not conduct it as
easily as a metal. As a result, the
circuit of the tester may be complete
and yet the current through it may be
too weak to make the bulb glow. Can
we make another tester which can
detect a weak current?
You may use an LED (Fig. 14.3) in
place of the electric bulb in the tester
of Fig. 14.2. LED glows even when a
weak electric current flows through
it.
There are two wires (called leads)
attached to an LED. One lead is
slightly longer than the other.
Remember that while connecting to
a circuit, the longer lead is always
connected to the positive terminal of
the battery and the shorter lead is
connected to the negative terminal of
the battery.
Fig. 14.3 : LEDs
We can use another effect of an electric
current to make another kind of tester.
Do you recall that electric current
produces a magnetic effect? What
happens to a compass needle kept nearby
when current flows in a wire? Even if
the current is small, the deflection of the
magnetic needle can be seen. Can we
make a tester using the magnetic effect
of currents? Let us find out.
Join the free ends of two wires
momentarily. The compass needle
should show deflection. Your tester
with two free ends of the wire is ready.
Now repeat Activity 14.2 using this
tester. Do you find a deflection in the
compass needle the moment you dip
the free ends of the tester in lemon
juice?
Take out the ends of the tester
from the lemon juice, dip them in
water and then wipe them dry.
Repeat the activity with other liquids
such as tap water, vegetable oil, milk,
honey. (Remember to wash and wipe
dry the ends of tester after testing each
liquid). In each case observe whether
the magnetic needle shows deflection
or not. Record your observations in
Table 14.1.
© NCERT
not to be republished
CHEMICAL EFFECTS OF ELECTRIC CURRENT 177
Table 14.1 : Good/Poor Conducting Liquids
S.No Material Compass Needle Shows Good Conductor/
Deflection Yes/No Poor Conductor
1. Lemon juice Yes Good Conductor
2. Vinegar
3. Tap Water
4. Vegetable oil
5. Milk
6. Honey
7.
8.
9.
10.
When the free ends of the
tester do not touch each
other, there is an air gap
between them. Paheli knows
that air is a poor conductor of
electricity. But she has also read
that during lightning, an electric
current passes through air. She
wonders if air is indeed a poor
conductor under all conditions.
This makes Boojho ask whether
other materials classified as
poor conductors also allow
electricity to pass under
certain conditions.
From Table 14.1, we find that some
liquids are good conductors of electricity
and some are poor conductors.
Actually, under certain conditions
most materials can conduct. That is why
it is preferable to classify materials as
good conductors and poor conductors
instead of classifying as conductors and
insulators.
We have tested the conduction of
electricity through tap water. Let us now
test the conduction of electricity through
distilled water.
Activity 14.4
Take about two teaspoonfuls of
distilled water in a clean and dry
plastic or rubber cap of a bottle. (You
may obtain distilled water from your
school science lab. You may also get
distilled water from a medical store
or a doctor or a nurse). Use the tester
to test whether distilled water
conducts electricity or not. What do
you find? Does distilled water
conduct electricity? Now dissolve a
pinch of common salt in distilled
water. Again test. What do you
conclude this time?
When salt is dissolved in distilled
water, we obtain salt solution. This is a
conductor of electricity.
The water that we get from sources
such as taps, hand pumps, wells and
ponds is not pure. It may contain several
© NCERT
not to be republished
SCIENCE 178
salts dissolved in it. Small amounts of
mineral salts are naturally present in it.
This water is thus a good conductor of
electricity. On the other hand, distilled
water is free of salts and is a poor
conductor.
Most liquids that conduct electricity
are solutions of acids, bases and salts.
When an electric current flows
through a conducting solution, does it
produce an effect on the solution?
14.2 Chemical Effects of
Electric Current
In Class VII, we have learnt some effects
of electric current. Can you list these
effects? What effect does the current
produce when it flows through a
conducting solution? Let us find out.
Activity 14.6
Take out carbon rods carefully from
two discarded cells. Clean their metal
caps with sand paper. Wrap copper
wires around the metal caps of the
carbon rods and join them to a
battery (Fig. 14.5). We call these two
rods electrodes. (Instead of carbon
Small amounts of mineral salts
present naturally in water are
beneficial for human health.
However, these salts make water
conducting. So, we should never
handle electrical appliances
with wet hands or while
standing on a wet floor.
W e have found that common salt, when
dissolved in distilled water, makes it a good
conductor. What are the other substances
which, when dissolved in distilled water,
make it conducting? Let us find out.
Caution: Do the next activity under the
supervision of your teacher/parent or
some elderly person, because the use of
acid is involved in it.
Activity 14.5
Take three clean plastic or rubber caps
of bottles. Pour about two teaspoonfuls
of distilled water in each of them. Add
a few drops of lemon juice or dilute
hydrochloric acid to distilled water in
one cap. Now in the second cap
containing distilled water, add a few
drops of a base such as caustic soda
or potassium iodide. Add a little sugar
to the distilled water in the third cap
and dissolve it. Test which solutions
conduct electricity and which do not.
What results do you obtain?
Fig.14.5 : Passing current through water
Metal Cap
Carbon
rod
Water
Carbon
rod
© NCERT
not to be republished
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