CBSE Class 8 Science Chapter 14: Chemical Effects of Electric Current NCERT Solutions

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NCERT Solutions PDF Class 8 PDF

This chapter delves into the fascinating world of chemical effects of electric current, crucial for Class 8 Science students. The NCERT Solutions provided here offer clear explanations and step-by-step solutions to all exercises. Students will learn about which liquids conduct electricity, the chemical changes that occur when current passes through solutions, and the process of electroplating. The solutions also cover the functioning of a tester and the reasons why a bulb might not glow. These resources are designed to help students grasp complex concepts, solve problems accurately, and prepare effectively for their examinations by reinforcing their understanding of electrical conductivity and its applications.

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BoardCBSE
ClassClass 8
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 14

Chapter summary

Chapter 14 of the Class 8 Science NCERT Solutions focuses on the Chemical Effects of Electric Current. It explains the concept of electrical conductivity in liquids, identifying substances like acids, bases, and salts as good conductors. The solutions detail the chemical effects that occur when electricity passes through solutions, including the deposition of metals. It also covers the practical application of electroplating and troubleshooting common issues with electrical testers. The exercises are designed to test understanding of these principles and their real-world implications.

Learning outcomes

  • Understand that many liquids conduct electricity when they are solutions of acids, bases, and salts.
  • Explain the chemical effects that occur when electric current passes through a conducting solution.
  • Identify the process of electroplating and its applications.
  • Analyze the reasons why a bulb in an electrical tester might not glow.
  • Compare the electrical conductivity of different liquids based on experimental observations.

Topics covered

Paper topics

  • Electrical Conductivity of Liquids
  • Acids, Bases, and Salts as Conductors
  • Chemical Effects of Electric Current
  • Electric Testers
  • Deflection of Magnetic Needle
  • Distilled Water vs. Tap Water Conductivity
  • Electroplating
  • Applications of Electroplating
  • Troubleshooting Electrical Testers
  • Factors Affecting Conductivity

Important topics

  • Electrical conductivity in liquids
  • Chemical effects of electric current
  • Electroplating process and applications
  • Using an electric tester
  • Identifying conductors and insulators

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Questions and Solutions

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 _____.
Solution: (a) Most liquids that conduct electricity are solutions of acids, bases, and salts. These substances dissociate into ions in solution, which carry the electric charge. (b) The passage of an electric current through a solution causes chemical effects. These effects can include the deposition of metals, the production of gases, or changes in the solution's composition. (c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery. This is because the positively charged copper ions (Cu²⁺) in the solution are attracted to the negatively charged electrode (cathode). (d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating. This technique is widely used for decorative and protective purposes.

Question 2

When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Solution: The deflection of the magnetic needle indicates that an electric current is flowing through the circuit. When the free ends of the tester are dipped into a solution, if the solution is a conductor, it completes the electrical circuit. The flow of electric current through the wire connected to the magnetic needle generates a magnetic field, which causes the needle to deflect. Therefore, the deflection signifies that the liquid or solution being tested is a conductor of electricity.

Question 3

Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.
Solution: Three liquids that may cause the magnetic needle to deflect when tested are:
  1. Tap water (or groundwater): Contains dissolved salts and minerals, making it conductive.
  2. Vinegar: It is a dilute solution of acetic acid, which dissociates into ions and conducts electricity.
  3. Lemon juice (or other citric fruit juices): Contains citric acid, which makes the solution conductive.
In general, any liquid solution containing dissolved acids, bases, or salts will conduct electricity and cause the magnetic needle to deflect.

Question 4

The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.
Solution: If the bulb does not glow in the tester setup, it means the circuit is not complete or there is insufficient current to light the bulb. Possible reasons include:
  1. The liquid is not a conductor: For example, if the container holds distilled water, which has very few ions and thus conducts electricity poorly.
  2. The bulb is fused: A fused bulb has a broken filament, interrupting the flow of current.
  3. The battery is exhausted: If the battery has no remaining charge, it cannot provide the necessary electric current to make the bulb glow.
  4. Loose connections: There might be air gaps or loose connections in the wires, electrodes, or battery terminals, preventing the circuit from being completed.
For the bulb to glow, the circuit must be complete, the liquid must be conductive, the bulb must be functional, and the battery must have sufficient charge.

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:
  1. liquid A is a better conductor than liquid B.
  2. liquid B is a better conductor than liquid A.
  3. both liquids are equally conducting.
  4. conducting properties of liquid cannot be compared in this manner.
Solution: The correct conclusion is:
  1. liquid A is a better conductor than liquid B.
Explanation: The brightness of the bulb in an electric tester is directly related to the amount of current flowing through the circuit. A brighter glow indicates a higher current, meaning the liquid offers less resistance to the flow of electricity and is therefore a better conductor. Conversely, a dim glow indicates a lower current, signifying that the liquid is a poorer conductor.

Common mistakes

  • Confusing the positive and negative terminals in electroplating.
  • Assuming distilled water conducts electricity.
  • Not considering all possible reasons for a tester's failure (e.g., fused bulb, weak battery, loose connections).
  • Incorrectly identifying which liquid is a better conductor based on bulb brightness.

Revision tips

  • Review the definitions of key terms like conductor, insulator, electroplating, and chemical effects.
  • Draw diagrams of the tester setup to visualize how circuits are completed.
  • Practice identifying the conditions under which a liquid will conduct electricity.
  • Understand the role of the negative terminal in the deposition of metals during electrolysis.

Practice MCQs

Q1. Which of the following liquids are generally good conductors of electricity?

Q2. The process of depositing a thin layer of a desired metal onto another material using electricity is called:

Q3. When copper sulphate solution is electrolyzed, copper gets deposited on the plate connected to:

Q4. If the bulb in an electrical tester glows very dimly, it indicates:

Q5. Which of these is NOT a likely reason for a bulb not glowing in a tester setup?

Frequently asked questions

What are the main types of liquids that conduct electricity?

Liquids that conduct electricity are typically solutions of acids, bases, and salts. These substances dissociate into ions when dissolved in water, allowing for the flow of electric current.

What is electroplating and why is it important?

Electroplating is the process of depositing a thin layer of a desired metal onto another object using electric current. It's important for enhancing appearance, preventing corrosion, and improving durability of materials.

How does a magnetic needle help in testing electrical conductivity?

When electric current flows through a wire near a magnetic needle, it produces a magnetic field that causes the needle to deflect. This deflection indicates that current is passing through the solution being tested.

Why doesn't distilled water conduct electricity well?

Distilled water is very pure and contains very few dissolved ions. Since ions are necessary to carry electric charge, distilled water is a poor conductor of electricity.

What does it mean if the bulb in an electric tester glows brightly?

A bright glow indicates that the liquid is a good conductor of electricity, allowing a significant amount of current to flow through the circuit and the bulb.

How can these NCERT solutions help in exam preparation?

These solutions provide clear, step-by-step explanations for each question, helping students understand the underlying concepts, practice problem-solving techniques, and identify potential areas of difficulty for focused revision.

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