NCERT Solutions for Class 8 Science Chapter 11 Chemical Effects of Electric Current

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 _________.

Ans:  

a) Most liquids that conduct electricity are solutions of acids, bases and salts. 

(The solutions of acids, bases, and salts can conduct electricity because they produce ions when dissolved in water and allow an electric current to pass through them.) 

b) The passage of an electric current through a solution causes chemical effects. 

(A chemical reaction occurs when an electric current passes through a conducting solution. As a result, the solution decomposes into positive and negative ions. This process of decomposition of the solution is known as the chemical effect of electric current.) 

c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery. 

(Copper sulphate decomposes into positively charged copper ions and negatively charged sulphate ions when an electric current is passed through it. These positively charged copper ions get drawn towards the plate (cathode) connected to the negative terminal of a battery and get deposited on it.) 

d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

One of the most significant uses of the chemical effects of electric current is electroplating.

2. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason? 

Ans: The deflection in the magnetic needle of a compass shows that current is flowing through the wire, i.e., through the circuit. This shows that the circuit is complete since the free ends of the tester are dipped in a conducting solution. A conducting solution allows electric current to pass through it and, as a result, the magnetic needle shows a deflection.

3. Name three liquids, which when tested in the manner shown in Fig. 11.9, may cause the magnetic needle to deflect.

Ans: Liquids such as lemon juice, saltwater, and vinegar are conducting liquids that allow electricity to pass through them. Hence, these liquids can be used in the beaker to show the deflection of the magnetic needle.

4. The bulb does not glow in the setup shown in Fig. 11.10. List the possible reasons. Explain your answer.

Ans:  The bulb may not glow for one or more of the reasons listed below:

1. The liquid in the beaker is maybe poor conducting. As a result, the electric current would not be able to flow through the liquid. Hence, the circuit is incomplete.

2. The electric current in the circuit is too weak to light the bulb. This can happen if the material used to make the circuit is not a good conductor of electricity or if the battery does not have enough energy to generate electricity.

3. The liquid may have a very low conductivity. So, the current flowing through the circuit may be insufficient to produce enough heat in the filament of the bulb to make it glow.

4. The battery may be used up and no longer be capable of generating electricity.

5. The bulb may be fused.

6. Connections are loose.
   
   

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.

Ans:  

1. Liquid A is a better conductor than liquid B. 

The amount of current flowing through a conducting solution is determined by its conductivity. The greater the conductivity, the greater the amount of current passing through the solution, and vice versa. The conductivity of liquid A is greater than the conductivity of liquid B. Hence, liquid A is a better conductor than liquid B.

6. Does pure water conduct electricity? If not, what can we do to make it conduct?

Ans: No, pure water does not conduct electricity as it is a poor conductor of electricity. Pure water (distilled water) is devoid of any salts. They can conduct electricity when a small amount of common salt is added to them, as the salt solution allows electricity to pass through.

7. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply of the area. Explain why they do this.

Ans: Water usually contains salts and has the ability to conduct electricity. If the area's electrical supply is not turned off and water is poured on electrical appliances, electricity may pass through the water. Electricity may harm firemen if they come in contact with wet electrical switches, electric wires, and other electrical appliances. They may get electrocuted. That is why, in the case of a fire, the main electrical supply for the area is shut off before they use the water hoses, to prevent the firemen from electrocution.

8. A child staying in a coastal region test the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason? 

Ans: The amount of dissolved salts present in the seawater is more than the water we use for drinking purposes. As a result, seawater will conduct electricity better than drinking water. So, the compass needle shows more deflection in seawater than in drinking water.

9. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpours? Explain. 

Ans: No, it is not safe for an electrician to work on electrical appliances outdoors during a heavy downpour. This is because rainwater contains a small number of dissolved salts and acids, making it a good conductor of electricity. So, the electrician may get electrical shocks while working outdoors during heavy rains or downpours.

10. Paheli had heard that rainwater is as good as distilled water. So, she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle show deflection. What could be the reasons? 

Ans: Rainwater contains a small number of dissolved salts and impurities, making it a good conductor of electricity. Distilled water does not contain any dissolved salts or impurities; thus, it is a poor conductor of electricity. Hence, due to the presence of these salts and impurities, rainwater can allow electricity to pass through it and cause a deflection in the compass needle, while distilled water cannot.

11. Prepare a list of objects around you that are electroplated. 

Ans: The list of electroplated objects around us is as follows: 

1. Chromium plating: This is done on different parts of cars, motorcycles, and buses, to give them a shiny appearance. 

2. Gold Plating: A thin layer of gold is deposited by electroplating on the silver ornaments and they are called gold-plated ornaments. 

3. Zinc plating: Iron used in constructing buildings, bridges, and automobiles is coated with a layer of zinc (galvanization). This provides strength and protects the iron from corrosion and rusting.
   
   

12. The process that you saw in Activity 11.7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the battery and why?

Ans: The thick rod of the impure copper plate is to be attached to the positive terminal of the battery. This is because when the electric current is passed through the copper sulphate solution, it gets dissociated into positively charged copper ions and negatively charged sulphate ions. The free copper, being positively charged, gets attracted to the negative terminal of the battery and gets deposited on the electrode (cathode) attached to it. The loss of copper from the copper sulphate solution is regained from the impure copper rod (anode) connected to the positive terminal of the battery.

Class 8 Science Chapter 11- Quick Overview of Detailed Structure of Topics

Class 8 Science Chapter 11 - Important Points

• Electric current can bring about chemical changes in substances. This phenomenon is known as the chemical effect of electric current.

• Substances that conduct electricity in their aqueous state are called electrolytes (e.g., acids, bases, salts). Non-electrolytes do not conduct electricity in any state (e.g., sugar, alcohol).

• Electroplating is the process of depositing a metal layer on another material using electricity. It is used to improve appearance, prevent corrosion, and enhance conductivity.

• Electrolysis is the process of decomposing electrolytes into their constituent elements using electricity. For example, electrolysis can split water into hydrogen and oxygen gases.

• The chemical effects of electric current find applications in various fields, such as the electroplating of metals, electrochemical cells (like batteries), and industries where corrosion prevention is crucial.

• Factors like the type of electrolyte, current intensity, duration of plating, and the material being plated affect the quality and efficiency of electroplating.

• Electric current can also cause corrosion when metals react with substances in their environment. Understanding this phenomenon helps in developing methods to prevent corrosion.

Benefits of Referring to Vedantu’s Chemical Effects Of Electric Current Class 8 PDF

• Class 8 Chemical Effects Of Electric Current Questions And Answers offer clear explanations of concepts covered in the chapter, ensuring students grasp the principles of the chemical effects of electric current thoroughly.

• Electric Current Class 8 covers essential topics such as electrolytes, conductors, and non-conductors, detailing their roles in chemical reactions induced by electric current.

• Detailed methodologies for solving problems related to the chemical effects of electric current are provided, helping in practical application and understanding.

• Class 8 Science Chapter 11 Question Answer assists students in efficient last-minute revision, strengthening their knowledge and enhancing exam preparation.

• Chemical Effects Of Electric Current Class 8 solutions are presented in a structured format, facilitating easy navigation through different sections and topics of the chapter.

• By referring to the to the Chemical Effects Of Electric Current Class 8 PDF, students can effectively prepare for exams, as the solutions comprehensively cover all key topics and potential exam questions.

• Students can utilise Class 8 Science Chapter 11 Question Answer PDF solutions to evaluate their understanding, identifying areas for further practice or clarification.

Conclusion

Vedantu’s NCERT Solutions for Class 8 Science Chapter 11 - Chemical Effects of Electric Current is an excellent resource for students. They simplify complex concepts like electrolysis and electroplating, ensuring clarity and understanding. With step-by-step solutions, students grasp practical applications of electric currents, focusing on key topics like chemical reactions and conductors. The solutions include practice questions that align with the previous year's papers to enhance exam preparation. By utilising these resources, students can strengthen their understanding of electrical chemistry, preparing them effectively for assessments while gaining practical insights into how electricity impacts chemical processes.

Important Study Materials For Class 8 Science Chapter 11 Chemical Effects of Electric Current

For more insights, students can also download additional study materials provided by Vedantu for Chapter 11 of CBSE Class 8 Science Solutions-

NCERT Solutions for Class 8 Science - Chapter-wise Links

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