Viii Chapter 14

Chapter-14
Chemical Effects of Electric Current

1. Fill in the blanks:
(a) Most liquids that conduct electricity are solutions of acids, bases and salts.
(b)The passage of an electric current through a solution causes chemical
effects.
(c)If you pass current through copper sulphate solution, copper gets deposited
on the plate connected to the negative terminal of the battery.
(d)The process of depositing a layer of any desired metal on another material by
means of electricity is called electroplating.
2. When the free ends of a tester are dipped into a solution, the magnetic
needle shows deflection. Can you explain the reason?
A-Yes, the solution is a good conductor of electricity. The reason is that the
solution is a good conductor of electricity, so the needle get deflected.
3. Name three liquids, which when tested in the manner shown in fig 14.9,
may cause the magnetic needle to deflect.
A-3 Lemon juice, salt water and vinegar.

4.The bulb does not glow in the setup shown in fig.14.10. List the possible
reasons. Explain your answer.
A- If the bulb does not glow it may be because of some reasons like the bulb
may be fused, replaced with a new bulb. If it still does not glow, it shows that
the connection of wires may be loose. After tightening connections if still the
bulb does not glow, then it is sure that the solution does not conduct electric
current.
5.A tester is used to check the conduction of electricity through two liquids,
labelled A and B. It is found that the bulb of the tester glows brightly for
liquid A while it glows very dimly for liquid B. You would conclude that
(i) liquid A is a better conductor than liquid B.
(ii)liquid B is a better conductor than liquid A.
(iii)both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this manner.
A-(i) Liquid A is a better conductor than liquid B.
The amount of current flowing through a conducting solution depends on the
conductivity of the solution. With more conductivity, more current passes
through the solution and vice versa. Hence the conductivity of liquid A is more
than the conductivity of liquid B.
6.Does pure water conduct electricity? If not, what can we do to make it

conducting?
A-No, pure water does not conduct electricity. This is because pure water is
devoid of any salts. Pure water can conduct electricity when a pinch of common
salt is added to it, as salt solution is conducting in nature.
7. In case of a fire, before the firemen use the water hoses, they shut off the
main electrical supply for the area. Explain why they do this.
A-Water is a good conductor of electric current. If the electrical supply for the
area is not shut off and water is poured over electrical appliances, then
electricity may pass through water and harm the firemen and other people. That
is why, in case of a fire, the firemen shut off the electric supply for the area
before they use the water hoses.
8. A child staying in a coastal region tests the drinking water and also the
seawater with his tester. He finds that the compass needle deflects more in
the case of seawater. Can you explain the reason?
A- Drinking water has been processed and purified before supplying it to the
houses. Many salts and minerals have been removed from it, so it has decreased
its conductivity. On the other hand the sea water is rich in salts, other acids and
basic substances, that is why it is a better conductor of electricity and deflects
the needle more than the purified drinking water.
9. Is it safe for the electrician to carry out electrical repairs outdoors
during heavy downpours? Explain.
A-No, it is highly dangerous to carry on electric repairs in water, as water is a
good conductor of electricity. It can cause electrocution.
10. Paheli had heard that rainwater is as good as distilled water. So, she
collected some rainwater in a clean glass tumbler and tested it using a
tester. To her surprise she found that the compass needle showed
deflection. What could be the reasons?
A-10 While it rains, the raindrops get mixed with the suspended particles of the
air. So, they do not remain pure. It becomes the mixture of salts and other
impurities thus show conduction of electricity.
11. Prepare a list of objects around you that are electroplated.

A-Following objects around us are electroplated-
(i) Chromium plating is done on different parts of cars, buses and motorcycles
to give them shiny appearance.
(ii) A fine layer of gold is deposited on the silver ornaments and they are called
gold plated ornaments.
(iii)Iron used in bridges and automobiles is coated with a layer of zinc. This
protects iron from corrosion and rusting.
(iv)Tin cans used for storing food, are made by electroplating tin on to iron.
Thus food does not come in contact with iron and is protected from getting
spoilt.
12. The process that you saw in Activity 14.7 is used for purification of
copper. A thin plate of pure copper and a thick rod of impure copper are
used as electrodes. Copper from impure rod is sought to be transferred to
the thin copper plate. Which electrode should be attached to the positive
terminal of the battery and why?

A-The impure copper rod should be attached to the positive terminal because
the free copper will get drawn towards the negative terminal to be get deposited,
so the copper from impure rod will be collected in the pure copper plate .
ADDITIONAL QUESTIONS
1. Define the following:
(i)Good conductors of electricity-Materials which allow electric current to
pass through them are called good conductor of electricity.
(ii) Poor conductors of electricity-Materials which do not allow electric
current to pass through them easily are called poor conductors of electricity.
(iii)Electrodes-The metal rods dipped in liquids to which cells are attached are
called electrodes.
(iv) Electrolyte-It is a compound which either in aqueous solution or in the
molten state allows electric current to pass through it. It decomposes into
neutral atoms at the two electrodes.
(vi) Magnetic effect of electric current-Magnetic effect of electric current

means that an electric current flowing in a wire, produces a magnetic field
around it.
(vii)Chemical effects of electric current-The passage of an electric current
through a conducting liquid causes chemical reactions. The resulting effects are
called chemical effects of electric current.
(viii) Electroplating-The process of depositing a layer of any desired metal on
another material, by means of electricity is called electroplating.
(ix)Electrolysis-The process of decomposition of an electrolyte on passing
electricity through it, is called electrolysis.
For example- Hydrogen gas is evolved at cathode and oxygen gas is evolved at
anode during the electrolysis of water.
2. Why does a bulb glow when the electric current passes through it?
A-When electric current passes through a bulb, the filament of the bulb gets
heated up to a high temperature and it starts glowing. This is heating effect of
current.
7. How will you make a tester using magnetic effect of electric current?
A- Take the tray from inside a discarded matchbox. Wrap an electric wire a few
times around the tray. Place 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. 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 dip the free ends of the
tester in given liquids to test whether the liquid conduct electric current or not.
Q-9 Explain how the electric current produces the chemical effect on a
potato?
A-First cut a potato into two halves and inserted the copper wires of a tester into
it. After half an hour, we noticed that there was a greenish blue spot on the
potato where no such spot around the other wire. It was found that it was always
the wire connected to the positive terminal, which had a greenish blue spot
around it. It could be used for identifying the positive terminal of a cell or a
battery concealed in a box. This shows that current produced a chemical effect
in the potato.
Q-10 Explain the electroplating of copper on an iron spoon?

A-The experimental set up for electroplating copper on an iron spoon is as
shown in figure. The object (iron spoon) to be electroplated is made
cathode(negative electrode) .A thin sheet of pure copper is made anode(positive
electrode). An acidified solution of copper sulphate is used as electrolyte. When
electricity is passed through copper sulphate solution, the copper metal gets
electroplated on the iron spoon.
Fig: Electroplating
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Chapter-14

Chemical Effects of Electric Current

A-3 Lemon juice, salt water and vinegar.

6.Does pure water conduct electricity? If not, what can we do to make it

11. Prepare a list of objects around you that are electroplated.

terminal of the battery and why?

(vi) Magnetic effect of electric current-Magnetic effect of electric current

Q-10 Explain the electroplating of copper on an iron spoon?

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