NCERT Exemplar for Class 8 Science Solutions 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.

Ans: Electric current can produce the heating and chemical as well as the magnetic effect when it passes through a coil, a conducting solution or a circuit respectively.

Hence, the correct answer is (d).

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

Figure 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.

Ans: If the bulb in setup A is glowing more brightly than in the setup B, then it means that the current is higher in the circuit of setup A than in the setup B.

Hence, the correct answer is (a).

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.

Ans: The industrial waste must be taken care of before exposing it into the environment in order to protect nature from getting polluted. Industries must follow the disposal guidelines of the local authority.

Hence, the correct answer is (d).

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.

Ans: The changed colour of the conducting solution occurs due to the chemical effect of the electric current.

Hence, the correct answer is (a).

5. Which one of the following solutions will not conduct electricity?

(a) Lemon juice

(b) Vinegar

(c) Tap water

(d) Vegetable oil

Ans: Electric conductivity of solutions happens due to the presence of free ions. Here, the solutions of lemon juice, vinegar and tap water are ionic whereas vegetable oil does not release free ions in the normal conditions.

Hence, the correct answer is (d).

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

(a) Iron

(b) Copper

(c) Chromium

(d) Aluminium

Ans: Due to the shiny and scratch resistant nature of Chromium, it is used in electroplating of many objects.

Hence, the correct answer is (c).

7. 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

Figure 14.2

Ans: The three solutions except the sugar solution will release free ions in a solution but the sugar solution in diluted water cannot give free ions for the conduction of electricity.

Hence, the correct answer is (d).

Very Short Answer Questions

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.

Ans: The words to be filled in the given blank spaces are as follows:

(a) Cathode

(b) Electroplating

(c) Conductor

(d) Chromium

9. Why is a layer of zinc coated over iron?

Ans: To prevent iron from getting corroded i.e. rusted, the contact of iron from air is avoided by coating a layer of zinc over the iron. This keeps the iron rust free and makes the object last longer.

10. Will the solution of sugar in distilled water conduct electricity?

Ans: In any solution, free ions are needed for the conduction of electricity. However, free ions are not generated in a sugar solution in distilled water, hence it does not conduct electricity.

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

Ans: The bulb glows due to the heating effect of electric current. The filament of a bulb is made up of elements such as Tungsten, which has a high melting point so that it glows without breaking due to higher temperature.

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.

Figure 14.3

Ans: This could happen due to insufficient electricity generated by the cell which was not enough to glow the bulb. Adding one more cell increases the electricity upto the required amount and hence the bulb glows.

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.

Ans: The bulb did not glow in the liquid B but the LED glows because LED needs lesser amount of electricity than a bulb to glow. The liquid B may not be a better conductor of electricity than the liquid A, and may not be releasing enough free ions in the solution in order to conduct electricity efficiently. This results in the bulb not glowing but then the LED glows.

14. 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?

Ans: The spoon should be connected to the negative terminal of the battery and the other electrode must be made up of silver so that the silver starts getting depleted on the spoon due to electrolysis.

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

Ans: Iron reacts with oxygen and gets oxidised which may spoil the food contained in it. This is why tin is electroplated on iron as tin is less reactive and prevents the food from oxidation.

16. Observe Fig. 14.5.

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

Ans: The electrons flow from the negative terminal towards the right terminal and then these electrons react with the potato and the end of the positive terminal which then turns the potato greenish blue. Hence, circuit A shows the correct observation.

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.

Ans: Iron and steel can conduct electricity while coal and eraser can not conduct electricity. Therefore:

(a) No

(b) Yes

(c) No

(d) Yes

Long Answer Questions

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

Ans:  Following observations may be possible in this case:

(a) The temperature of the solution may increase due to the heating effect of electric current.

(b) Bubbles of gas may be possibly seen on the electrodes.

(c) The colour of the solution may change.

(d) Deposition of metal on the electrodes may also occur.

19. In the circuit given as Fig. 14.7, 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 a negative electrode. Will copper be still deposited on the carbon rod? Explain your answer.

Ans: Yes, copper will be deposited on the carbon rod as a negative electrode. When electricity passes through the copper sulphate solution, it dissociates the solution into copper cations and sulphate anions. These copper ions get deposited on the negative electrode because they are positively charged ions.

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.

Ans: Following steps can be taken for the purification of copper in the given circuit:

(i) Plate A made up of pure copper.

(ii) Plate B made up of impure copper.

(iii) Copper Sulphate as the solution.

When electricity is passed through the copper sulphate solution, it dissociates into copper and sulphate ions. These copper ions have positive charge, hence they get deposited on the negative terminal which is made up of pure copper. This process is known as electroplating.

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.

Ans: Yes, air is a poor conductor of electricity because it has no free electrons or charged particles to conduct electricity in normal conditions. In certain conditions, such as lightning, air can also conduct electricity because the particles present in the air get charged due to lightning and may be able to conduct electricity.

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.

Ans: If the water is normal or tap water then it may conduct electricity but if it is distilled water then it can not conduct electricity because distilled water does not have free ions. In this case, adding a few drops of lemon juice is necessary in order to make the solution salty i.e. ionic so that it conducts electricity. When the current flows through this solution, bubbles of gas can be seen emerging on the electrodes.

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.

Figure 14.11 A                                                       Figure 14.11 B

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

Ans: The deflection in magnetic compass occurs due to the magnetic effect of electric current.

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

Ans: The current present in the circuit may not be enough upto the amount of electricity that is required to light the bulb.

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

Ans: If the number of turns in the coil wound around the magnetic compass is increased, then the deflection shown by the compass will also increase.

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

Ans: If the numbers of cells are increased in the circuit, then the deflection shown by the compass will also be increased.

24. You are provided with a magnetic compass, an empty matchbox, 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.

Ans: The required circuit diagram can be shown by the figure drawn below:

In the above given, the magnetic compass will show deflection when the electric current passes through the circuit. In this way, the flow of electric current can be tested using the given materials.

Introduction- Chapter 14-Chemical Effects of Electric Current

Class 8 Science NCERT Exemplar Solutions Chapter 14 Chemical Effects of Electric Current by Vedantu provided here gives you answers to all the questions you have. Vedantu allows you to download it with just one click.  This book has answers to all the types of questions that can be asked in the examination. It can be multiple choice questions, very short answer questions, short answer questions, long answer questions.  The students need to study NCERT exemplar solutions by Vedantu to get a better understanding of each topic of Chapter 14 - Chemical effects and Electric current and score good marks in Class 8th final examination. 

Chapter 14- Chemical effects and Electric current explain how different chemicals react when an electric current moves through it. In this chapter, students will study which chemicals are good conductors of electricity and which chemicals are poor conductors of electricity. To gain detailed knowledge for this chapter it is recommended to solve the NCERT Exemplar and you can get an idea of what type of questions can be asked from this chapter.

You can download a PDF of NCERT Exemplar Class 8 Science Solutions for Chapter 14 – Chemicals Effects Of Electric Current and get the complete guide to prepare this chapter for your exams.

Important Topics-  Class 8 Science Chapter 14 Chemical Effects of Electric Current

Vedantu experts have studied and short-listed some of the important topics that are frequently asked in exams from Chapter 14 chemical effects of electric current. The list of important topics are given below:

• Do Liquids Conduct Electricity?

• Chemical Effects of Electric

• Electroplating.

In a student's life, Class 8th is one of the very important stages in which students start participating in scholarship exams and other exams like science olympiad, etc. the NCERT exemplar solutions provide you with a complete understanding of the topic which enables you to clear your concepts and score higher marks.