CBSE Class 8 Science Chapter 14: Chemical Effects of Electric Current NCERT Solutions
This chapter delves into the fascinating world of chemical effects of electric current, a key topic in CBSE Class 8 Science. The NCERT Solutions provided here offer detailed explanations and step-by-step solutions to all exercises. Students will learn about the conductivity of liquids, understanding why certain solutions conduct electricity while others do not. The solutions cover concepts like electrolytes, the process of electrolysis, and its applications such as electroplating. By working through these problems, students will grasp how electric current can cause chemical changes and how this phenomenon is utilized in various industrial processes. These solutions are designed to aid in thorough exam revision, ensuring a strong understanding of the chapter's core principles.
Quick info
| Board | CBSE |
|---|---|
| Class | Class 8 |
| Subject | Science |
| Session | 2026 |
| Language | English |
| Type | NCERT Solutions |
| Chapter | Chapter 14: Chemical Effects of Electric Current |
Chapter summary
Chapter 14 of the CBSE Class 8 Science curriculum focuses on the Chemical Effects of Electric Current. The NCERT Solutions cover the conductivity of liquids, distinguishing between conductors and insulators. It explains the chemical reactions that occur when current passes through solutions, introducing the concept of electrolysis. Key applications like electroplating are also discussed. The solutions provide clear answers to exercise questions, helping students understand the practical implications of electric current in chemical processes.
Learning outcomes
- Understand that most liquids that conduct electricity are solutions of acids, bases, and salts.
- Explain the chemical effects caused by the passage of electric current through a solution.
- Identify the role of the negative terminal in the deposition of metals during electrolysis.
- Define and explain the process of electroplating.
- Differentiate between good and poor conductors of electricity based on the brightness of a bulb in a tester.
- Recognize that distilled water does not conduct electricity.
Topics covered
Paper topics
- Conductivity of Liquids
- Electrolytes
- Electric Tester
- Chemical Effects of Current
- Electrolysis
- Deposition of Metals
- Electroplating
- Applications of Electrolysis
- Acids, Bases, and Salts as Conductors
- Distilled Water Conductivity
Important topics
- Conductivity of Liquids
- Electrolysis Process
- Electroplating
- Chemical Effects
- Role of Terminals in Deposition
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Questions and Solutions
Question 1
(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 _____.
The blanks can be filled as follows:
(a) Most liquids that conduct electricity are solutions of acids, bases and salts. These substances dissociate into ions when dissolved in water, making the solution conductive.
(b) The passage of an electric current through a solution causes chemical effects. This is because the current can initiate chemical reactions within the solution.
(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 are attracted to the negative electrode.
(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
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 of electricity, it completes the electric circuit. The flow of electric current through the tester's wire generates a magnetic field around it, which causes the magnetic needle to deflect. Therefore, the deflection signifies that the liquid is a conductor of electricity.
Question 3
(Note: Fig. 14.9 typically shows a tester setup with a battery, bulb, and electrodes dipped in a liquid.)
A magnetic needle will deflect if the liquid conducts electricity. Three such liquids are:
- Vinegar: It is a dilute solution of acetic acid, which contains ions and conducts electricity.
- Tap water (or Ground water): It contains dissolved salts and minerals, making it conductive.
- Lemon juice: It is acidic due to citric acid and thus conducts electricity.
In general, any liquid solution containing acids, bases, or salts will conduct electricity and cause the magnetic needle to deflect.
Question 4
(Note: Fig. 14.10 typically shows a circuit with a battery, bulb, and electrodes dipped in a liquid, where the bulb is not lit.)
If the bulb does not glow in the tester setup, it means the circuit is not complete or the current flowing is too weak. Possible reasons include:
- The liquid is not a conductor: If the liquid in the container is distilled water, pure alcohol, or oil, it does not contain enough ions to conduct electricity, and the circuit remains open.
- Fused bulb: The bulb itself might be fused or burnt out, preventing it from lighting up even if current is flowing.
- Exhausted battery: The battery may have run out of charge, providing insufficient voltage or current to light the bulb.
- Loose connections: There might be loose connections in the circuit, such as the wires not being properly attached to the battery terminals, the bulb holder, or the electrodes. An air gap between the electrodes and the liquid can also break the circuit.
Question 5
- liquid A is a better conductor than liquid B.
- liquid B is a better conductor than liquid A.
- both liquids are equally conducting.
- conducting properties of liquid cannot be compared in this manner.
The correct conclusion is: liquid A is a better conductor than liquid B.
Explanation: The brightness of the bulb in an electric tester is an indicator of the amount of electric current flowing through the circuit. A brighter glow means more current is flowing, which implies the liquid is a better conductor. Conversely, a dim glow indicates that less current is flowing, meaning the liquid is a poorer conductor. Since the bulb glows brightly for liquid A and dimly for liquid B, liquid A allows more current to pass through it than liquid B, making it a better conductor.
Common mistakes
- Confusing the positive and negative terminals during metal deposition.
- Assuming distilled water conducts electricity.
- Not understanding that the brightness of the bulb indicates the conductivity of the liquid.
- Incorrectly identifying substances that act as electrolytes.
Revision tips
- Review the definitions of conductor, insulator, electrolyte, and electrolysis.
- Understand the setup of an electric tester and how it indicates conductivity.
- Focus on the process and applications of electroplating.
- Practice identifying which liquids are likely to conduct electricity and why.
Practice MCQs
Q1. Which of the following are typically good conductors of electricity when dissolved in water?
Explanation: Acids, bases, and salts dissociate into ions in water, making the solution electrically conductive.
Q2. The process of depositing a thin layer of one metal onto another using electric current is called:
Explanation: Electroplating is the specific term for using electricity to coat one metal with another.
Q3. When copper sulphate solution is electrolyzed, on which terminal does copper get deposited?
Explanation: Positively charged copper ions (Cu²⁺) are attracted to the negatively charged electrode (cathode) and get deposited there.
Q4. Why does the bulb glow dimly in liquid B compared to liquid A in the tester setup?
Explanation: A dimmer glow indicates less current flow, meaning liquid B is a poorer conductor than liquid A.
Q5. Which of the following liquids is generally a poor conductor of electricity?
Explanation: Distilled water lacks ions and therefore does not conduct electricity well.
Frequently asked questions
What are the chemical effects of electric current?
When electric current passes through a conducting liquid, it can cause chemical changes, such as the deposition of metals or the formation of bubbles of gas. These are known as the chemical effects of electric current.
Why are solutions of acids, bases, and salts good conductors of electricity?
These solutions contain ions (charged particles) that are free to move. When an electric field is applied, these ions move towards the oppositely charged electrodes, allowing the current to flow through the solution.
What is electroplating and why is it useful?
Electroplating is the process of depositing a thin layer of a desired metal onto another object using electrolysis. It is useful for protecting metals from corrosion, improving their appearance, or making them harder.
Does distilled water conduct electricity? Why or why not?
No, distilled water is a poor conductor of electricity because it contains very few ions. Pure water molecules do not readily dissociate into ions.
How does a magnetic needle help in testing the conductivity of liquids?
If a liquid is a conductor, it allows electric current to pass through it, completing a circuit that includes a magnetic needle. The flowing current creates a magnetic field around the wire, causing the needle to deflect.
What is the role of the negative terminal in electroplating copper?
When electroplating copper from a copper sulphate solution, the object to be plated is connected to the negative terminal (cathode). The positively charged copper ions (Cu²⁺) in the solution are attracted to this negative terminal and get deposited on it.
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