Lesson: Chemical Effects of Electric Current

Question: 1

An electric current can produce:

(a) Heating effect only

(b) Chemical effect only

(c) Magnetic effect only

(d) Chemical, heating, and magnetic effects

Solution:

d

Question: 2

Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in the figure below. They found that the bulb in the setup A glows more brightly as compared to l that of the setup B. You would conclude that:

(a)   Higher current is flowing through the circuit in setup A.

(b)   Higher current is flowing through the circuit in setup B.

(c)   Equal current is flowing through both the circuits.

(d)   The current flowing through the circuits in the two setups cannot be compared in this manner.

Solution:

a

Question: 3

Boojho’s uncle has set up an electroplating factory near his village. He should dispose-off the waste of the factory

(a) In the nearby river.

(b) In the nearby pond.

(c) In the nearby cornfield.

(d) According to the disposal guidelines of the local authority.

Solution:

d

Question: 4

When electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates:

(a) The chemical effect of current

(b) The heating effect of current

(c) The magnetic effect of current

(d) The lightning effect of current

Solution:

a

Question: 5

Which one of the following solutions will not conduct electricity?

(a) Lemon juice

(b) Vinegar

(c) Tap water

(d) Vegetable oil

Solution:

d

Question: 6

Which of the following metals is used in electroplating to make objects appear shining?

(a) Iron

(b) Copper

(c) Chromium

(d) Aluminium

Solution:

c

Question: 7

Which of the following solutions will not make the bulb in the figure below glow?

(a) Sodium chlorides

(b) Copper sulphate

(c) Silver nitrate

(d) Sugar solution in diluted water

Solution:

d

VERY SHORT ANSWER QUESTIONS (4)

Question: 1

Fill in the blanks:

(a)   The object to be electroplated is taken as ____________electrode.

(b)   One of the most common applications of chemical effect of electric current is ______________.

(c)   Small amount of a mineral salt present naturally in water makes it a ______________ of electricity.

(d)   Electroplating of ______________ is done on objects like water taps and cycle bell to give them a shiny appearance.

Solution:

(a) Cathode

(b) Electroplating

(c) Conductor

(d) Chromium

Question: 2

Why is a layer of zinc coated over iron?

Solution:

Zinc protects iron from corrosion and rust. Hence, a layer of zinc is coated over iron.

Question: 3

Will the solution of sugar in distilled water conduct electricity?

Solution:

No. Solution of sugar in distilled water will not conduct electricity.

Question: 4

Name the effect of current responsible for the glow of the bulb in an electric circuit.

Solution:

Heating effect caused due to flowing of electric current is responsible for the glow of the bulb in an electric circuit.

SHORT ANSWER QUESTIONS (6)

Question: 1

Boojho made the circuit given in the figure given below and observed that the bulb did not glow. On Paheli’s suggestion he added one more cell in the circuit. 

The bulb now glows. Explain.

Solution:

By adding one more cell in the circuit, there is an increase in the supply of current flowing through the bulb so, the bulb glows.

Question: 2

Paheli set up an experiment using liquid A in the beaker as shown in the figure below. She observed that the bulb glows. Then she replaced the liquid A by another liquid B. This time the bulb did not glow. Boojho suggested replacing the bulb by an LED. They observed that the LED glows. Explain.

Solution:

The current flowing through liquid B could be weak. Therefore, Paheli was unable to make the bulb glow. However, the current was strong enough for the LED to glow.

Question: 3

Paheli wants to deposit silver on an iron spoon. She took silver nitrate (AgNO3) solution in a beaker and setup a simple circuit for electroplating. Which terminal of the battery should the spoon be connected to? What material should the other electrode be made of?

Solution:

The spoon should be connected to the negative terminal of the battery. The other electrode should be made of silver.

Question: 4

Why is tin electroplated on iron to make cans used for storing food?

Solution:

Tin is less reactive than iron. Tin coating on iron prevents iron from getting in contact of food material, thus preventing it from getting spoiled.

Question: 5

Which of these two circuits A or B shows the correct observation?

Solution:

Circuit A shows the correct observation.

Question: 6

Observe the following circuits carefully. In which circuit will the bulb glow? Write ‘Yes’ or ‘No’ for each of the circuit given in the figure below.

Piece of coal

Iron nail

Eraser

Steel spoon

Solution:

No. A piece of coal is a poor conductor of electricity. Hence, the bulb will not glow.

Yes. An iron nail is a good conductor of electricity. Hence, the bulb will glow.

No. An eraser is a poor conductor of electricity. Hence, the bulb will not glow.

Yes. A steel spoon is a good conductor of electricity. Hence, bulb will glow.

LONG ANSWER QUESTIONS (7)

Question: 1

An electric current is passed through a conducting solution. List any three possible observations.

Solution:

·         Gas bubbles may be formed on the electrodes.

·         The solution may get heated.

·         Deposits of metal may be seen on the electrodes.

·         The colour of the solution may get changed.

Question: 2

In the circuit given in the figure below, Boojho observed that copper is deposited on the electrode connected to the negative terminal of the battery. Paheli tried to repeat the same experiment. But she could find only one copper plate. Therefore, she took a carbon rod as negative electrode. Will copper be still deposited on the carbon rod? Explain your answer.

Solution:

Yes. Copper from the copper plate will be dissolved into the copper sulphate solution, and from there, it will get deposited on the carbon rod by electroplating.

Question: 3

Observe the circuit given in the figure below. Boojho set up this circuit for purification of copper. What will be the nature of:

(a) Plate A

(b) Plate B

(c) The solution.

Explain the process of purification.

Solution:

(a) Plate A – MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaaieaaju gGbabaaaaaaaaapeGaa83eGaaa@3978@                    Pure copper

(b) Plate B – MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaaieaaju gGbabaaaaaaaaapeGaa83eGaaa@3978@                   Impure copper

(c) The solution – MathType@MTEF@5@5@+= feaagKart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaaieaaju gGbabaaaaaaaaapeGaa83eGaaa@3978@          Copper sulphate

Copper from the impure copper plate is transferred to the pure copper plate by the process called electroplating.

Question: 4

Observe the following circuit given in the figure below. Current does not flow in the circuit if there is a gap between the two wires. Does it indicate that air is a poor conductor of electricity? Does air never conduct electricity? Explain.

Solution:

Yes. Air is a poor conductor of electricity.

However, during lightning, there is a high voltage in the air which may turn it into a conductor of electricity.

Question: 5

Boojho made the circuit shown in the figure below. 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.

Solution:

Distilled water is free of salts and is therefore a poor conductor. If the water taken by Boojho is distilled water and lemon juice is not added to it, current will not pass through the circuit. If the water taken is salty, a weak current will pass through the circuit. This will be seen as bubbles on the negative electrode.

Question: 6

Observing that the bulb does not glow in the circuit shown in figure A, Boojho changed the circuit as shown in figure B. He observed deflection in the magnetic compass.

(a)   What does the deflection in magnetic compass indicate?

(b)   Why did the bulb not glow in figure A?

(c)   What would be the effect of increase in the number of turns in the coil wound around the magnetic compass?

(d)   What will be observed if the number of cells is increased in the circuit shown in figure B?

Solution:

(a)   The deflection in magnetic compass indicates the presence of current in the circuit.

(b)   The bulb in the figure A did not glow because the current was not sufficient enough to make it glow.

(c)   Deflection in the magnetic compass will increase.

(d)   If the number of cells is increased in the circuit shown in the figure, the deflection in the magnetic compass will increase further.

Question: 7

You are provided with a magnetic compass, an empty match box, a battery of two cells and connecting wires. Using these objects show how will you make a tester for testing an electric circuit? Draw the necessary circuit diagram and explain.

Solution:

A tester for testing an electric circuit can be made by creating magnetic field using two wires. This can be done by the following procedure:

·         Take the tray from the matchbox.

·         Wrap an electric wire few times around the tray.

·         Place the magnetic compass inside the tray.

·         Connect one free end of the wire to the terminal of a battery and 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 the two wires. The compass needle should show deflection.

Whenever current flows through the circuit, the magnetic compass needle shows deflection due to the magnetic effect of current.