6. Electroplating of copper
If we take two copper
rods and connect them
with positive and
negative terminals of a
battery respectively ,
then after a while if
we take out the two
electrodes we see that
copper rod connected
to negative terminal
turns thick and the
other turns thin
Positive
terminal
Copper rod
Negative
terminal
Copper rod
7. TOPICS TO BE COVERED
Application of
electroplating
Advantages
of
electroplating
.
NCERT
exercises
Worksheet
14. 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) acids, bases, salts
(b) chemical
(c) negative
(d) electroplating
NCERT EXERCISES
15. 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 in magnetic needle shows that the circuit is complete and the solution conducts electricity,
i.e., it is a good conductor.
Question 3.
Name three liquids, which when tested in the manner shown in Fig. 14.5. may cause the magnetic needle
to deflect.
Answer:
Vinegar, lemon juice and tap water.
Question 4.
The bulb does not glow in the setup shown in Fig. 14.6. List the possible reasons. Explain your answer.
Answer:
The bulb may not glow because of the following reasons:
(i) The wires in the circuit may be loosely connected.
(ii) The bulb may be fused.
(iii) The cells may be used up.
(iv) The liquid may be an insulator, i.e., a poor conductor of electricity.
16. 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
(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.
Answer:
(i) liquid A is a better conductor than liquid B.
Question 6.
Does pure water conduct electricity? If not, what can we do to make it conducting?
Answer:
No, pure water doesn’t conduct electricity. But when salt is dissolved in pure water, it conducts electricity.
Question 8.
A child staying in a coastal region test 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?
Answer:
The seawater contains a huge amount of salts in comparison to drinking water, hence the seawater is a
better conductor of electricity and it produces a stronger magnetic field in the wire and hence deflects the
compass needle more.
To be done in notebook
17. 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:
Rainwater is pure water which is an insulator but it gets mixed with air pollutants like sulphur dioxide and nitrogen
oxides and form acidic solution, which is a good conductor of electricity. So, the compass needle showed
deflection.
Question 11.
Prepare a list of objects around you that are electroplated.
Answer:
Objects that are electroplated are door handles, taps, rims of cycles, showers, the handlebar of cycles and bikes,
gas burner, tin cans, metallic almirahs, buckles of belts, etc.
Question 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?
Answer:
The thick rod of impure copper plate is to be attached to the positive terminal of the battery because when electric
current is passed through the copper sulphate solution, it gets dissociated into copper and sulphate. The free
copper, being positively charged, gets drawn to the negative terminal of the battery and gets deposited on it. On
the other hand the loss of copper from the solution is regained from the impure copper rod which is attached to
the positive terminal of the battery.
Question number 10 and 11 to be done in notebook
18. WORKSHEET
Level-1
1. Fill in the blanks:
A. …………….. effect of electric current makes the bulb glow
B.The needle of magnetic compass ……………. When it is brought near a wire where the current
flows.
C. The object to be electroplated is taken as ____________ electrode.
D. One of the most common applications of chemical effect of the electric current is ______________.
E. Electroplating of ______________ is done on objects like water taps and cycle bells to give them a
shiny appearance.
F. _____________ is the material used for electroplating cans used for storing food.
Answer
A. Chemical
B. Deflects
C. Negative
D. Electroplating
E. Chromium
F. Tin
19. LEVEL-2
Answer the following:-
1. Why is it suggested to use LED light in a tester instead of an ordinary bulb?
Give reasons why
1.We can make a tester using a compass.
2.Bubbles are produced during electrolysis of water.
3. Electrodes should be good conductors of electricity.
4. Graphite despite being a non metal can be used as an electrode.
2. Why are the objects instead of chromium plating not made of chromium itself?
3. Mention advantages and disadvantages of electroplating?
4. Which metals apart from chromium are used for electroplating other metals?
Answers
1. LED light is suggested to use in a tester instead of an ordinary bulb because LED glows even when a weak electric
current flows through it.
Give reasons why
1. The needle of compass shows deflection even when a weak current flows due to magnetic effect of electric current.
2. Water upon electrolysis produces hydrogen at cathode and oxygen at anode , hence bubbles are produced.
3. Electrodes should be good conductor of electricity otherwise electricity cannot flow through it.
4. Graphite is a good conductor of electricity despite being a non metal. Hence it is used as electrodes.
20. ,2. Objects are not made of chromium because chromium is expensive and it may not be
to make the whole object out of chromium. So the object is made from a cheaper metal and
only a coating of chromium over it is done.
3. Advantages of electroplating are:-
1. It is used to coat metal surfaces with desired metal coatings, for decoration purposes.
2. It saves metal surfaces from rusting.
3. It saves corrosion of surfaces of metals.
Disadvantages of electroplating are:-
1. The disposal of waste products produced during the process of electroplating is a major
problem. The waste conducting solution pollutes the environment.
2. The process requires multiple coating of the metal, which is time consuming.
3. The cost of setting up the apparatus is high.
4. Some typical metals other than chromium that are used for electroplating are Gold,
Silver, Nickel, Tin etc.
21. LEVEL-3 CLASS WORK
1. Which of the following solutions will not make the bulb glow in the setup of a liquid conductor?
(a) sodium chlorides
(b) zinc sulphate
(c) copper nitrate
(d) sugar solution in diluted water
Ans. (d) sugar solution in diluted water will not make the bulb glow in the setup of a liquid
conductor.All the rest are salt which can dissociate into ions and conducts electricity.
2. Boojho wants to test the conduction of electric current of a liquid. He has two testers in one of
which a bulb is used and in the other magnetic compass is used. Which tester would you suggest
him to use and why?
Ans. I would suggest to use magnetic compass instead of bulb because the needle can show
deflection in presence of weak current
3. Why are electric fires extinguished with either using a CO2 extinguisher or mud but not water?
Ans. Water is a very good conductor of electricity because it consist of various impurities which
makes it a good conductor of electricity. Hence if we use water to extinguish electric fire there is a
possibility of getting electrocuted.
22. 4. During electrolysis of water oxygen bubbles are formed near which electrode?
Ans. During electrolysis of water oxygen bubbles are formed near the positive electrode.
5. Suppose you want to deposit silver on an iron spoon using silver nitrate as electrolyte.
Which terminal of the battery should you connect the spoon to?
Ans. The spoon to be electroplated should be connected to the negative terminal of the
battery because the desired metal will get deposited on the electrode connected to the
negative terminal of the battery
6. Boojho made a circuit using distilled water. He wanted to observe what happens when
an electric current is passed through water. But he forgot to add a few drops of lemon
juice to water. Will it make any difference to his observations? Explain.
Ans.No current will pass through the circuit, if the water is distilled water and lemon juice
is not added. If the water is salty, a small current will pass through the circuit. Adding few
drops of lemon juice in water will increase the conductivity of the solution and large
amount of current will flow easily.
23. Now please unmute your mics and
let us end our class by laughing
out loud.
