CHEMICAL EFFECT OF CURRENT
SYLLABUS: Good conductor, poor conductor, electrode, anode, cathode, electrolyte, voltmeter, LED, Testing of conduction
through liquid, electrical conductivity of liquid can be explained by a simple activity, chemical effect of current, electricity
through acidulated water, electrolysis, application of electrolysis, electroplating, steps of electroplating, uses of electroplating,
drawbacks of electroplating, heating effect of current, magnetic effect of current.
INTRODUCTION
We are often instructed to do not touch any electrical appliances with wet hands. Ever
wondered why?
We see almost all the electrical appliances in our house are connected through wires and the
current flows through these wires. So basically we have seen that current flows through solid
(ex. wires). But what about liquids? Do current also flows through Liquid? If yes, then what are
their effects and where do we use them. So all these thing will be discussed in this chapter.
GOOD CONDUCTORS
Electric current can easily pass through some materials. Such materials are called good
conductors of electricity, e.g. iron, copper, silver, aluminum, gold, acidic solution, salt solution
etc.
POOR CONDUCTORS OR INSULATORS
Electric current cannot pass easily through some materials. Such materials are called bad
conductors of electricity, e.g. rubber, wood, asbestos, plastic, honey, milk, vegetable oil etc.
ELECTRODE
A solid electric conductor through which an electric current enters or leaves an electrolytic cell
or other medium.
ANODE
The electrode connected to the positive terminal of the battery.
CATHODE
The electrode connected to the negative terminal of the battery.
ELECTROLYTE
The solution or the paste which contains the electrodes and conducts the current through itself
is electrolyte.
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VOLTMETER
A voltmeter, also known as a voltage meter, is an instrument used for measuring the potential
difference, or voltage, between two points in an electrical or electronic circuit.
1. LED
LED is abbreviated as Light Emitting Diode.
An LED is enclosed in a glass housing; with two wires (called lead) coming out. One lead is
slightly longer than another and connected to positive terminal of the battery.
An electric bulb is used in the electric circuit, to confirm the flow of the current in the circuit.
However if the electric current is weak the bulb may not glow and in this case the LED is used.
An LED can glow even in the presence of weak current.
It must be ensure that the free ends of the LED should not touch each other.
These are available in many colors in the market.
2. TESTING OF CONDUCTION THROUGH LIQUID
Pure or distilled water is a bad conductor of electricity.
Whereas sea water, tap water, lemon juice, liquid soap, rain water, salt solution, etc is good
conductor of electricity because they contain dissolved salts.
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ELECTRICAL CONDUCTIVITY OF LIQUID CAN BE EXPLAINED BY SIMPLE ACTIVITY
Take lemon juice in a container, insert two electrodes in it, and connect them to the terminals
of a battery with a LED between them.
It glows, indicating that lemon juice is a conductor of electricity.
Different liquids can be checked for electrical conductivity in the same way.
On passing electricity through a conducting solution, the molecules of the solution dissociate
into ions, which cause electrical conduction through the liquid. This process is due to the
chemical effect of electric current.
3. CHEMICAL EFFECT OF CURRENT
(a) When electric current is passed through water, water dissociates into hydrogen and oxygen.
(b) When electric current is passed through the solution of a metal salt, such as solution of
copper sulphate, metal gets deposited at the negative pole, because metal is positively
charged.
(c) Sometimes, the color of solution also changes when electric current passes through it.
(d) Electrolysis
(e) Electroplating
Let’s understand all these in detail.
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ELECTRICITY THROUGH ACIDULATED WATER
-When electrodes were immersed in acidulated water and current was passed -through water;
bubbles of oxygen and hydrogen were produced.
-Oxygen bubbles were formed at the electrode connected to the positive terminal. --Hydrogen
bubbles were formed at the electrode connected to the negative terminal.
4. ELECTROLYSIS
The process of causing a chemical change in a solution by passing the electric current through it
is called electrolysis.
During electrolysis at least one of the following phenomena may occur –
a. Gas bubbles are evolved at the electrodes.
b. Color of the electrolyte solution changes.
c. A metal get deposited at the negative electrode or cathode.
5. APPLICATION OF ELECTROLYSIS
It was discovered by Johann Wilhelm Ritter. It is widely used in chemical and commercial
industries for the following purposes-
a. Refining of impure metals into pure ones.
b. Extraction of metals into pure ones.
c. Electroplating
6. ELECTROPLATING
The process of depositing a layer of a desired metal on any other material by means of
electricity is called electroplating.
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7. STEPS OF ELECTROPLATING
1. The material which needs to be coated with a layer is made cathode.
2. The metal which is to be coated is made anode.
3. The electrolyte or the conducting solution is made of a salt of desired metal.
Electric current is passed through the solution.
4. When the current is passed through the salt solution of the metal, it starts depositing on the
surface of the cathode from its solution.
5. On the other hand, from the anode equal amount of metal gets dissolved in the solution and
thus restore the loss from the solution.
The electroplating is done on the item and the metal is transferred from one electrode to
another.
When electric current is passed through copper sulphate solution the copper sulphate
(CuSO4)get dissociated into Cu2+ and SO42- ions.
As a result the Cu2+ ions started moving towards the positive terminals, leading to the
deposition of copper on the electrode connected to the negative terminal.
Also, from the electrode which was connected to the positive terminal, the copper got released
into the solution, making the solution blue in color.
In this case, the process is a continuous and reversible.
CuSO4 ⇆ Cu2+ + SO42-
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9. USES OF ELECTROPLATING
1. Water pipes, which made of iron, are coated with a layer of zinc metal by the process of
electroplating. Zinc is less reactive than iron and thus prevents the iron pipe from getting
rusted. Applying a layer of zinc on an article is called anodizing.
2. Applying a layer of chromium on an article by this method is called chrome plating. Rims of
wheel of cycle, cars, etc. are electroplated with chromium metal. It gives them shiny
appearance and prevents from rust.
3. Jewels made of silver or other cheap metals are electroplated with gold to give them
appearance like gold.
4. Tin cans used for storing food are made of iron electroplating with a coat of tin. Tin is less
reactive than iron, and prevent foods packed in them from getting spoiled.
5. It is done for the decoration purposes. Eg A flower vase of brass if electroplated with silver
looks more attractive.
6. Very small parts of the machines cannot be repaired easily. Such parts are repaired by
depositing the desired metal at the proper location electrolytic ally.
10. DRAWBACKS OF ELECTROPLATING
It results in production of many harmful chemicals whose disposal always remains a big
environmental problem.
The chrome plate itself is not toxic, but most chrome plating is done in a bath of chromic acid,
which is considered carcinogenic hazards such as chrome sores, chrome ulcers etc.
Despite of all these hard facts chrome plating is still popular in industry because of low cost,
easy processing and the range of applications.
11. HEATING EFFECT OF CURRENT
When electric current passes through a conductor, it increases the temperature of the
conductor. This is called heating effect of electric current.
Many electrical appliances work on heating effect of electric current, e.g. electric bulb, water
heater, electric iron, etc.
12. MAGNETIC EFFECT OF CURRENT
When electric current passes through a conductor, a magnetic field is created around the
conductor. This is called magnetic effect of electric current.
This can be demonstrated by keeping a magnetic compass near a current-carrying conductor.
A magnetic compass shows deflection when it is placed near a current carrying conductor.
The devices which work on magnetic effect of electric current are: electric motor and
electromagnet.
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OBJECTIVE QUESTION
1. Copper wire is
a. An insulator b. A conductor
c. Both of these d. None of these
2. Materials which do not conduct electric current are known as
a. conductors b. metals
c. insulators d. solutions
3. A solid electric conductor through which an electric current enters or leaves an electrolytic
cell is known as
a. Electrolysis b. Electrode
c. Metal d. Insulator
4. The electrode connected to the positive terminal of battery is known as
a. Cathode b. Anode
c. Metal Plate d. Non Metal Plate
5. An instrument used for measuring the potential difference, or voltage, between two points in
an electrical or electronic circuit is known as
a. Voltmeter b. Ammeter
c. Electric Meter c. current meter
6. What is full form of LED?
a. Light electric diode b. Light emitting diode
c. Light exhausting diode d. Light energy diode
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7. Why we use LED instead of electric bulb in an electric circuit?
a. Because it is cheaper than electric bulb
b. Because it can glow even when the current is weak
c. Because it is compulsory to use LED in an electric circuit
d. Because they are available in all the colors in the market
8. A man is swimming in the pool and the electric current is passed through the water in pool.
However the man was safe. Which of the following statement about the water in the pool is
true?
a. It is salty water b. It is tap water
c. It is distilled water d. It is mixture of distilled and lemon water.
9. On passing electricity through a conducting solution, the molecules of the solution dissociate
into ions, which cause electrical conduction through the liquid. This process is due to the
a. Chemical effect of electric current.
b. Magnetic effect of electric current
c. Heating effect of electric current
d. Lightening effect of electric current
10. When electric current is passed through water, water dissociates into
a. Hydrogen and Nitrogen. b. Hydrogen and Oxygen
c. Oxygen and Nitrogen d. Oxygen, Hydrogen and Nitrogen
11. When electric current is passed through the solution of a metal salt, such as solution of
copper sulphate, metal gets deposited at the negative pole, because metal is
a. Positively Charged. b. Negatively Charged
c. Neutral d. Insulator
12. In LED the longer lead is connected to
a. Positive terminal of battery b. Negative terminal of battery
c. Either positive or negative d. None of these
13. When current is passed through acidulated water
a. Bubbles of oxygen and hydrogen were produced.
b. Oxygen bubbles were formed at the electrode connected to the positive terminal.
c. Hydrogen bubbles were formed at the electrode connected to the negative terminal.
d. Allare correct
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14. The process of causing a chemical change in a solution by passing the electric current
through it is called
a. Electrolysis b. Electroplating
c. Electrochemistry d. Noneof these
15. during electrolysis which of the following phenomena may not occur –
a. Gas bubbles are evolved at the electrodes.
b. Color of the electrolyte solution changes.
c. A metal get deposited at the negative electrode or cathode.
d. Solution gets evaporated
16. Which of the following is not the use of electrolysis
a. Refining of impure metals into pure ones.
b. Extraction of metals into pure ones.
c. Electroplating
d. None of these
17. The process of depositing a layer of a desired metal on any other material by means of
electricity is called
a. Electroplating. b. Electrolysis
c. Electrochemistry d, None of these
18. In electrolysis the material which needs to be coated with a layer is made
a. Cathode b. Anode
d. Either cathode or anode d. None of these
19. The metal which is to be coated is made
a. Cathode b. Anode
d. Either cathode or anode d. None of these
20. When electric current is passed through copper sulphate solution the copper sulphate
(CuSO4)get dissociated into
a. Cu2+ and SO42- ions. b. Only SO42- ions.
c. Only Cu2+ ions d. None of these
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21. To prevent iron from corrosion it is electroplated with
a. copper b. zinc
c. aluminum d. oxygen
22. Rims of wheel of cycle, cars, etc. are electroplated with chromium metal because it gives
them
a. Shiny Appearance b. Preventsfrom rust
c. Both (a) and (b) d. None of these
23. The chrome plate itself is not toxic, but most chrome plating is done in a bath of chromic
acid, which is considered carcinogenic hazards such as chrome sores, chrome ulcers
etc.Despite of all these hard facts chrome plating is still popular in industry because of
a. Low Cost b. Easy Processing
c. Range Of Applications. d. All of these
24. Which of the following electrical appliances do not work on heating effect of electric
current?
a. Electric Bulb b. Water Heater
c. Electric Iron d. Washing Machine
25. When electric current passes through a conductor, a magnetic field is created around the
conductor. This is called
a. Magnetic Effect of electric current.
b. Heating Effect of electric current.
c. Chemical Effect of electric current.
d. Lightening Effect of electric current.
ANSWERS
1. b 2. c 3. b 4. b 5. a 6. b 7. b
8.c 9. a 10. b 11. a 12. a 13. d 14. a
15. d 16. d 17. a 18. a 19. b 20. a 21. b
22. c 23. d 24. d 25. a
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SUBJECTIVE QUESTION
1. Define the following terms-
Electrode, anode, Cathode, Electrolyte
2. What is LED? What are the advantages of using LED over an electric bulb?
3. What happens when electricity is passed through the conducting solution?
4. Explain Chemical effect of electric current?
5. What is meant by electrolysis?
6. Explain application of electrolysis?
7. Which effect of current causes the bulb to glow?
8. Why it is dangerous to touch the electrical appliances with wet hands
9. How do you test weather a liquid solution conduct or do not conduct electricity?
10. Why we are able to test the conduction of electric current using magnetic compass?
11. All that glitter is not gold “justify this statement with reference to electroplating.
12. With the help of an experiment show electrolysis of water.
13. Explain the various effects of electric current.
14. What are the drawbacks related to electrolysis?
15. Explain how electroplating help in prevention of iron from rusting?
NCERT EXERSICE
Q.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__________effect.
(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 metallic object, by means
of electricity, is culled __________.
Ans.
(a) Acids, Bases, Salts
(b) Chemical
(c) Negative
(d) Electroplating.
Q.2. When the free ends of a tester are dipped into a solution the magnetic needle shows
deflection. Can you explain the reason?
Ans. The magnetic needle will show deflection when circuit is complete.
The deflection of magnetic needle shows that the solution is a good conductor.
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Q.3. Name three liquids, which when tested in the manner shown in Mg. 14.1 may cause the
magnetic needle to deflect.
Ans. Tap water, hydrochloric acid, sodium hydroxide.
Q.4. The bulb does not glow in the set up shown in Fig .14.2. List the possible reasons. Explain
your answer.
Ans. The possible reasons may be:
(i) The connections of the circuit may be loose.
(ii) Bulb may b fused.
(iii) Cells may be used up.
(iv) The liquid may be poor conductor.
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Q.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 r an.rr.er, Ans, We
conclude that option (i) ‘liquid A is a better conductor than liquid B'.
Q.6. Does pure water conduct electricity? If not what can we do to make it conducting?
Ans. No, the pure water does not conduct electricity. Pure water can be made conduct'
dissolving salt in it.
Q.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.
Ans. The water used in water hoses is good conductor of electricity. Firemen shut off the main
electrical supply, because if the supply of electricity continues this may be high risk of
electrocution due to water.
Q.8. A child staying in the coastal region tests the drinking water and also the sea water with his
tester. He finds that the compass needle deflects more in the case of sea water. Can you
explain the reason?
Ans. Sea water contains more amount of salt than drinking water. So the sea water is a better
conductor of electricity. This is the reason that the compass needle deflects more in case of sea
water.
Q.9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy down-
pour? Explain.
Ans. No, it is not safe for the electrician t carry out electrical repairs during heavy downpour.
It is because during heavy downpour there is a higher risk of electrocution.
Q.10. Paheli had heard that rain. Water is as good as distilled water. So she collected some rain
water 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?
Ans. Rain water is like a distilled water but some impurities are mixed in from the atmosphere.
These impurities make the rain water conducting. This could be the reason for the deflection of
compass needle.
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Q.11. Prepare a list of objects around you that are electroplated.
Ans. Pots of metals, bath taps, ornaments, rims of vehicles, handle bar of cycles and motor
cycles, kitchen gas burner, bottom of cooking utensils, handles of doors, tin cans are the some
objects around us that are electroplated.
Q.12. Themes 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 Trans cued to the thin copperplate. Which electrode should be attached to the
positive terminal of the battery and why?
Ans. The rod of copper plate should be connected to the positive terminal of the battery.
Because when electric current is passed through the copper sulphate solution, it dissociates
into copper and sulphate. The free copper drawn to the negative terminal of the battery gets
deposited on it. On the other hand the loss of copper from the solution would be regained from
the impure copper rod which is connected to the positive terminal of the battery.
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