Chapter 14: Chemical Effects of Electric Current

MULTIPLE CHOICE QUESTIONS

1. An electric current can produce
(a) heating effect only.
(b) chemical effect only.
(c) magnetic effect only.
(d) chemical, heating, and magnetic effects.
Answer: (d) chemical, heating, and magnetic effects.

[ Electric current can heat a conductor, cause chemical changes in solutions, and produce a magnetic field around a wire when current flows.]

2.Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in Fig.14.1.

   
                                         Fig.14.1
They found that the bulb in the setup A glows more brightly as compared to 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.

Answer: (a)higher current is flowing through the circuit in setup A.

[The brightness of a bulb depends on the current ; therefore, a brighter bulb in setup A indicates a higher current is flowing through its circuit .]

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.
Answer: (d) according to the disposal guidelines of the local authority.

[ Factory waste may contain harmful chemicals, so it must be treated and disposed safely as per rules to avoid pollution of water, soil and environment.]

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.
Answer: (a) the chemical effect of current.

[ When current passes through a solution, chemical reactions occur which can change the colour of the solution. This is called the chemical effect of electric current.]

5.Which one of the following solutions will not conduct electricity?
(a) lemon juice      (b) vinegar    (c) tap water  (d) vegetable oil
Answer: (d) vegetable oil

[ Vegetable oil does not contain free ions, so it cannot allow electric current to pass through it. Hence, it does not conduct electricity. ]

6.Which of the following metals is used in electroplating to make objects appear shining?
(a) iron       (b) copper           (c) chromium    (d) aluminium

Answer: (c) chromium

[ Chromium is used in electroplating because it gives a shiny appearance and also protects objects from rust and corrosion.]

7.

  

                           Fig 14.2

Which of the following solutions will not make the bulb in Fig 14.2 glow?
(a) sodium chlorides        (b) copper sulphate
(c) silver nitrate               (d) sugar solution in diluted water
Answer: (d)sugar solution in diluted water .

[The sugar solution is a non-electrolyte. It lacks free ion to conduct electricity between the electrodes , so the circuit remains incomplete and the bulb does not glow. ]

8. 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 .

Answer: (a) The object to be electroplated is taken as negative electrode (cathode).

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

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

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

9. Why is a layer of zinc coated over iron?
Answer: Zinc is coated over iron to protect it from rusting. This process is called galvanization. Zinc prevents iron from coming in contact with air and moisture.

10. Will the solution of sugar in distilled water conduct electricity?
Answer: No, because sugar solution does not have free ions (charged particles) to conduct electricity.

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

Answer: The glow of a bulb in an electric circuit is due to the heating effect of electric current. The filament gets heated and becomes white hot, producing light.

SHORT ANSWER QUESTIONS

12. Boojho made the circuit given in Fig. 14.3 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.

  

Answer: Adding another cell increases the voltage, which pushes more current through the circuit. The stronger current provides enough energy for the bulb’s filament to glow.  

13. Paheli set up an experiment using liquid A in the beaker as shown in Fig. 14.4. 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.

                  Fig. 14.4

Answer: Liquid B is a weak conductor . The electric current passing through it is too weak to heat the bulb’s filament enough to make it glow. However, an Led glows even with a very weak current , which is why it lights up when the bulb does not .

14. Paheli wants to deposit silver on an iron spoon. She took silver nitrate () 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 ?

Answer: The spoon should be connected to the negative terminal (cathode). The other electrode should be made of pure silver (anode).

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

Answer: Tin is electroplated on iron to make food cans because tin is less reactive than iron. It protects the iron from rusting and does not react with the food or its acids. This keeps the food safe and prevents spoilage.

16. Observe Fig. 14.5

      

                         Fig. 14.5

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

Answer: Circuit A shows the correct observation.

In circuit A, the positive terminal of one cell is connected to the negative terminal of the next, allowing current to flow. This flow creates a magnetic effect that deflects the compass needle. In circuit B, the cell are connected incorrectly, so no current flows.

17. Observe the following circuits carefully. In which circuit will the bulb glow. Write ‘Yes’ or ‘No’ in the blank space provided along each of the circuit given in Fig. 14.6.

Answer: kkkkkkkkkkkkkkkkkkkkkkkkk

LONG ANSWER QUESTIONS

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

 Answer: When electric current is passed through a conducting solution, three possible observations are:

(i) Bubbles of gas may form at the electrodes.

(ii) Colour change of the solution may occur.

(iii) Deposit of metal may be seen on one of the electrodes

19. In the circuit given as Fig. 14.7, Boojho observed that copper is deposited on the electrode connected to the negative terminal 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.

 

Answer: Yes, copper will still be deposited on the carbon rod.

When electric current passes through the copper sulphate solution, free copper ions (positively charged) are attracted to the negative terminal. They deposit on the carbon rod, regardless of its material, as long as a copper plate is at the positive terminal.

20. Observe the circuit given in Fig. 14.8.

Boojho set up this circuit for purification of copper. What will be the nature of – (i) plate A (ii) plate B (iii) the solution. Explain the process of purification.

Answer: Plate A is impure copper (anode), and plate B is pure copper (cathode). The solution is acidified copper sulphate.

When current passes, copper dissolves from the impure plate and deposits onto the pure plate. Impurities settle at the bottom, resulting in purified copper on plate B.

21. Observe the following circuit given in Fig. 14.9

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.

Answer: Yes, under normal conditions, air is a poor conductor (insulator). However, air can conduct electricity under extreme conditions, such as during lightning , when very high voltage causes the air to break down and allow current to flow. Therefore, air is not a perfect insulator in all situations.

22. Boojho made the circuit shown in Fig. 14.10. 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.

Answer: Yes, Pure water is a poor conduct of electricity. Adding lemon juice (an acid) makes water a good conductor by providing ions. Without it, the current may be too weak to produce visible gas bubbles at the electrodes, making the experiment unsuccessful .  

23. Observing that the bulb does not glow in the circuit shown in Fig. 14.11 A, Boojho changed the circuit as shown in Fig 14.11 B. He observed deflection in the magnetic compass.

 

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

(ii) Why did the bulb not glow in Fig.14.11 A ?

(iii) What would be the effect of increase in the number of turns in the coil wound around the magnetic compass in Fig. 14.11B ?

(iv) What will be observed if the number of cells are increased in the circuit shown in Fig. 14.11B ?

Answer: (i) The deflection indicates that electric current is flowing through the circuit, as the current produces a magnetic effect that moves the needle.

(ii)  The bulb did not glow because the current was too weak to heat the filament sufficiently, even though the liquid was conducting electricity.

(iii) Increasing the turns increases the magnetic effect, which result in a larger deflection of the magnetic compass needle.

(iv) Increasing the cells increases the voltage, which increases the current flow, resulting in a greater deflection of the compass needle.

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

Answer:  Wrap the connecting wire around the matchbox several times to form a coil. Connect this coil, the battery, and the two free wire ends in a series circuit. Place the magnetic compass near the coil. When the circuit is complete, current flows, producing a magnetic field that deflects the compass needle, showing that current is passing. This deflection acts as the test.

Photo /diagram