NCERT Solution
CHEMICAL EFFECTS OF ELECTRIC CURRENT Chap 11
Exercises
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REPRODUCTION IN ANIMALS NIMALS
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Question 1
Fill in the blanks.
(a) Most liquids that conduct electricity are solutions of
..............., ............... and ...............
(b) The passage of an electric current through a solution
causes ............... effects.
(c) If you pass current through copper sulphate solution,
copper gets deposited on the plate connected to the ............... terminal of
the battery.
(d) The process of depositing a layer of any desired metal on
another material by means of electricity is called ...............
Answer
(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.
Question 2
When the free ends of a tester are dipped into a solution,
the magnetic needle shows deflection. Can you explain the reason?
Answer
The deflection of the magnetic needle can be explained by the
flow of current through the wounded wire of the tester. When the free ends of a
tester are dipped into a solution, the circuit becomes complete and current
starts flowing through the solution proving that the solution is a good
conductor of electricity. The current then flows through the wire creating a
magnetic field that deflects the magnetic needle.
Question 3
Name three liquids, which when tested in the manner shown in Fig.11.9, may cause the magnetic needle to deflect.
Answer
1. Saltwater
2. Lemon juice
3. Vinegar
Question 4
The bulb does not glow in the setup shown in Fig.11.10. List the possible reasons. Explain your answer.
Answer
Potential reasons for the bulb not glowing include:
1. The bulb might be defective or fused or the battery might be
dead.
2. If the bulb and battery are replaced and the bulb still fails
to light up, it suggests there could be issues with the connectivity, such as
loose or faulty connections.
3. If after checking and fixing the connections, the bulb still
doesn't glow, it means that the solution in the setup doesn't let electricity
pass through.
Question 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
1. liquid A is a better conductor than liquid B.
2. liquid B is a better conductor than liquid A.
3. both liquids are equally conducting.
4. conducting properties of liquid cannot be compared in this
manner.
Answer
Liquid A is a better conductor than liquid B.
Reason — The
brightness of the bulb is determined by the current through the circuit, which
in turn depends on the conductivity of the solution. The greater the
conductivity, the greater will be the quantity of current passing through the
solution and as a result the bulb will glow brightly. Hence, liquid A is a
better conductor than liquid B as the bulb glows more brightly in liquid A.
Question 6
Does pure water conduct electricity? If not, what can we do
to make it conduct?
Answer
Distilled or pure water is free from salts and is a bad
conductor of electricity.
When common salt (Sodium Chloride, i.e., NaCl) is dissolved
in water, it becomes a good conductor.
Question 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.
Answer
Water from hoses contain salts which makes the water
conducting and when that conducting water is sprayed in order to stop the fire,
it might result in spread of electric current if water is spilled over
electrical switches. Hence, firemen shut off the main electrical supply for the
area under fire.
Question 8
A child staying in a coastal region tests the drinking water
and also seawater with his tester. He finds that the compass needle deflects
more in the case of seawater. Can you explain the reason?
Answer
The amount of salts dissolved in seawater is more than that
in drinking water. So, seawater will be a better conductor than drinking water.
Hence, sea water shows increased deflection of the needle as compared to the
drinking water.
Question 9
Is it safe for the electrician to carry out electrical
repairs outdoors during heavy downpours? Explain.
Answer
It is unsafe for an electrician to conduct electrical repairs
outdoors during heavy downpours. Rainwater, containing dissolved salts, serves
as a good conductor of electricity. If it comes into contact with electrical
components or wiring, it can establish a path for the electric current, posing
a risk of electric shock to the electrician.
Question 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?
Answer
The deflection of the compass needle in Paheli's rainwater
sample could be due to the presence of dissolved ions or impurities in the
rainwater. While rainwater is generally considered relatively pure, it can
still pick up impurities from the atmosphere, such as dust, gases, or salts.
These salts can make the rainwater conductive to some extent causing it to
conduct electricity slightly and affect the behavior of
the compass needle.
Question 11
Prepare a list of objects around you that are electroplated.
Answer
Some of the common objects around us that are electroplated
are:
1. Car parts, bath taps, kitchen gas burners, bicycle
handlebars, wheel rims are electroplated with chromium as it has a shiny
appearance.
2. Ornaments are electroplated with gold or silver.
3. Tin cans, used for storing food, are made by electroplating
tin onto iron.
4. Bridges and automobiles are made of iron, which can rust
easily. Hence, they are electroplated with zinc to protect it from corrosion
and rust.
Question 12
The process that you saw in Activity 11.7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the 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?
Answer
The thick rod of impure copper should be attached to the
positive terminal of the battery in the purification process of copper. This is
because, during the passage of electric current through copper sulphate
solution, it breaks down into copper and sulphate ions. The positively charged
copper ions are attracted to the negative terminal of the battery, where they
get deposited on the thin plate of pure copper. Simultaneously, the impure
copper rod, linked to the positive terminal, contributes copper ions to
compensate for the loss in the solution. This ensures the overall purification
of copper during the process.
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