NCERT Class 8 Science Chapter 11 ‘Chemical Effects of Electric Current’: Notes and Solutions (Free PDF)

In order to thoroughly understand the concepts of a chapter, well-written notes are a must. Along with properly covering the chapter they also serve as a method of quick revision and help you ace your exams. Hence, keeping in mind the same, we have prepared NCERT Solutions and Notes for Class 8 Science Chapter 11: Chemical Effects of Electric Current. The best thing about these notes is that they are written in a point-wise manner thus making it easy to memorise them. After the notes, you will find solutions to the NCERT textbook exercises and a PDF of the same is available for you to download for future reference. Now, without any further ado let’s explore the notes.

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Class 8 Science Chapter 11: Chemical Effects of Electric Current

In this chapter, we are going to study the electric current, its conduction, the effects of electric current, electroplating, and related topics. All the above-mentioned topics are very interesting involving their process. So, let’s start with the notes.

Do Liquids Conduct Electricity?

There are certain materials such as copper, silver, aluminium, etc that conduct electricity, whereas materials such as rubber, and wood do not. But have you ever wondered if liquids conduct electricity? Let’s find out.

• When a circuit consisting of a battery, a cell, and a bulb is formed and the loose ends of the wires are dipped in a liquid such as lemon juice or vinegar, the bulb glows. This is because the liquid completes the circuit by conducting electricity and hence making the bulb glow. 
• Now the conducting strength of a liquid can be different and it can lead to different intensities of bulb filament glowing. This is because the liquid used may or may not conduct electricity as easily as a metal. 
• Examples of good conducting liquids include:- lemon juice, vinegar, salt water, etc.
• Examples of bad-conducting liquids include:- milk, honey, distilled water, etc.
• Tap water contains many salts in it, thus it is a good conductor of electricity.
• Most liquids that conduct electricity are solutions of acids, bases and salts.
• Distilled water doesn’t have any salts in it hence it does not conduct electricity. But when common salt is dissolved in it, it conducts electricity.

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• LED glows even when a weak electric current flows through it. 
• There are two wires (called leads) attached to an LED. One lead is slightly longer than the other. 
• Remember that while connecting to a circuit, the longer lead is always connected to the positive terminal of the battery and the shorter lead is connected to the negative terminal of the battery.

Chemical Effects of Electric Current

When an electric current is passed through a solution, does it have any effect on it? The answer to this lies in the next section of the chapter. And we will see what effects it has on the electrodes. Let’s explore the same.

• When an electric current is passed through a conducting solution, there is the formation of bubbles of gas at the electrodes indicating the chemical reaction occurring.
• On the electrode, there is the deposition of metal.
• Depending on the solution and the electrode used, there might be changes in the colour of the solution.

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Electroplating

The process of depositing a layer of desired metal over another material using electricity is known as electroplating. It is one of the most common applications of the chemical effects of electric current

• Example of electroplating: When an electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The free copper gets drawn to the electrode connected to the negative terminal of the battery and gets deposited on it. From the other electrode, a copper plate, an equal amount of copper gets dissolved in the solution.

Uses of electroplating:

Electroplating has many industrial applications. Some of them are mentioned below:

• Electroplating is a very useful process and is widely used in industry for coating metal objects with a thin layer of a different metal.
• Chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others to prevent them from corroding. Chromium is expensive hence, a cheaper metal is used and is electroplated with chromium. 
• Jewellery makers electroplate silver and gold on less expensive metals. These ornaments have the appearance of silver or gold but are much less expensive.
• Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.
• A coating of zinc is deposited on iron to protect it from corrosion and the formation of rust. This iron is then used in building bridges and automobiles.

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Important Definitions in NCERT Class 8 Science Chapter 11: Chemical Effects of Electric Current

Some important definitions covered in the chapter are mentioned below:-

• The process of depositing a layer of desired metal over another material using electricity is known as electroplating. It is one of the most common applications of the chemical effects of electric current.

Explore NCERT Solutions of all the Chapters of Class 8 Science:

Chapter 1	Chapter 2	Chapter 3
Chapter 4	Chapter 5	Chapter 6
Chapter 7	Chapter 8	Chapter 9
Chapter 10	Chapter 11	Chapter 12
Chapter 13

Download the NCERT Class 8 Science Chapter 11 Solutions PDF Here!

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

Let us now explore NCERT Solutions of Class 8 Science Chapter 11 to get answers to all writing

questions in the lesson Chemical Effects of Electric Current. 

Exercise Questions

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 _________.

Soln:

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

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

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

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

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

Soln:

After dipping both the ends of the tester into the solution, when the compass needle shows deflection it shows that it is conducting current and the circuit is complete. Hence, the solution is a conducting solution. 

3. Name three liquids, which when tested in the manner shown in Fig.14.9, may cause the magnetic needle to deflect.

Source: NCERT

Soln:

I. Saltwater

II. Lemon juice

III. Vegetable oil

These liquids can be taken into the beaker as they will conduct electricity and cause deflection in the needle. 

4. The bulb does not glow in the setup shown in Fig.14.10. List the possible reasons. Explain your answer.

Source: NCERT

Soln:

The reasons for the bulb not glowing in the above-shown set-up are:-

• The circuit is complete, but the liquid may be non-conducting hence not allowing electric current to flow.
• The circuit might be made up of such a material that is a bad conductor of electricity hence, the current may be weak.
• Battery might be inefficient in generating electricity.

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

(i) liquid A is a better conductor than liquid B.

(ii) liquid B is a better conductor than liquid A.

(iii) both liquids are equally conducting.

(iv) conducting properties of liquid cannot be compared in this manner.

Soln:

(i) Liquid A is a better conductor than liquid B.

The amount of current that will flow through the liquid is its conductivity. The greater the conductivity, the more current will flow and vice-versa. Hence, the conductivity is greater in liquid A than in liquid B. 

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

Soln:

No, pure water does not conduct electricity. This is because it lacks any salts and electrolytes that conduct the current. What we can do is, add common salt to it and then it will conduct electricity. 

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

Soln:

In case of a fire, the firemen shut off the main electrical supply of the area before using the water hose because water is a conductor of electricity, and can lead to harming of the firemen. Hence, the electrical supply is turned off to prevent firemen from getting in harm’s way. 

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

Soln:

Basic drinking water has less salt in it as compared to that of seawater. Because of this reason, seawater is a better conductor of electricity in comparison to drinking water. This will lead to the compass needles being deflected more in the case of seawater. 

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

Soln:

No, it is not safe for the electrician to carry out electrical repairs outdoors during heavy rains because the rainwater consists of many salts dissolved in it. These salts make the rainwater a good conductor of electricity and the electrician can get electrocuted because of it. 

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 showed deflection. What could be the reasons?

Soln:

The rainwater consists of many salts dissolved in it. These salts make the rainwater a good conductor of electricity, hence the compass needle deflects more.

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

Soln:

• Chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others to prevent them from corroding. Chromium is expensive hence, a cheaper metal is used and is electroplated with chromium. 
• Jewellery makers electroplate silver and gold on less expensive metals. These ornaments have the appearance of silver or gold but are much less expensive.
• Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.
• A coating of zinc is deposited on iron to protect it from corrosion and the formation of rust. This iron is then used in building bridges and automobiles.

12. The process that you saw in Activity 14.7 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?

Soln:

The impure, thick copper rod should be attached at the positive terminal of the battery because the copper-sulphate solution gets dissociated into copper and sulphate ions. Copper ions are positively charged, hence they get drawn towards the negative terminal of the battery and get deposited there. The copper that is lost from the solution is regained from the impure copper rod that is attached to the positive battery terminal.

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