Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14

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Class 8 Science Chapter 14 Extra Questions and Answers Chemical Effects of Electric Current

Extra Questions for Class 8 Science Chapter 14 Chemical Effects of Electric Current with Answers

Chemical Effects of Electric Current Class 8 Extra Questions Very Short Answer Type

Question 1.
Most liquids which conduct electricity are solutions of _________ and __________.
Answer:
salt, water

Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14

Question 2.
Do some liquids also conduct electricity?
Answer:
Yes, some liquids also conduct electricity, e.g., mercury (metal), impure water, aqueous solution of acids, bases, etc.

Question 3.
When current flows in a wire, a compass needle kept nearby gets deflected. What effect of current is this?
Answer:
This is magnetic effect of current.

Question 4.
Is air an insulator under all conditions?
Answer:
Only dry air is an insulator, but damp air is a conductor.

Question 5.
Is salt solution a conductor?
Answer:
Yes, it is.

Question 6.
Can there be made a coating of one metal on another?
Answer:
Yes, by electroplating, it can be done.

Question 7.
In electroplating, what effect of current is observed?
Answer:
Chemical effect.

Question 8.
In electroplating of copper, a layer of copper builds upon the plate. But, what about the loses of copper from the solution?
Answer:
From the other electrode, an equal amount of copper gets dissolved in the solution.

Question 9.
Why chromium is electroplated on other inferior material?
Answer:
Because it has shiny appearance, it does not corrode and resists scratches as well.

Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14

Question 10.
Though silver and gold jewellery is expensive, we can get ornaments in the market which have the appearance of silver or gold at much less prices. How is this possible?
Answer:
Jewellery makers electroplate silver and gold on less expensive metals. These ornaments have the appearance of silver or gold but are much less expensive.

Chemical Effects of Electric Current Class 8 Extra Questions Short Answer Type 1

Question 1.
Define conductors.
Answer:
Materials which allow electric current to pass through them are called conductors, e.g., aluminium, copper, etc.

Question 2.
Define insulators.
Answer:
Materials, which do not allow electric current to pass through them are known as insulators or non-conductor, e.g., rubber, plastic, wood, paper, etc.

Question 3.
Do liquids also conduct electricity?
Answer:
Yes, some liquids also conduct electricity. But, all liquids do not conduct electricity, e.g., Tap water can conduct electricity, but distilled water cannot.

Question 4.
What precaution is taken in regard of the cell, while checking the tester? Why?
Answer:
While checking the tester, one must not join its free ends for more than a few seconds. Otherwise the cells of the battery will drain very quickly.

Question 5.
Sometimes even though the liquid allows the electric current to pass and the circuit is complete, bulb does not glow. What can be the reason?
Answer:
If the current through the circuit is too small, the filament of the bulb does not get heated to high temperature and it does not glow.

Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14

Question 6.
Why is tap water, a conductor of electricity?
Answer:
Tap water contains lots of mineral salts dissolved in it which make this water conductor of electricity.

Question 7.
Why is distilled water an insulator of electricity?
Answer:
Distilled water is free from impurities like salts, minerals, dust, etc., so it is an insulator of electricity.

Question 8.
What precaution should be applied while you handle an electrical appliance?
Answer:
We should never handle electrical appliances with wet hands or while standing on a wet floor, because electricity can conduct through the water and there could be an electrocution.

Question 9.
What can be done to make water more conductive?
Answer:
A teaspoon of salt or a few drops of lemon juice (acid) can be added into the water, to make it more conductive.

Question 10.
What is meant by the term electroplating?
Answer:
The process of depositing a layer of any desired metal on another metallic object by means of electricity is called electroplating.

Question 11.
Why is zinc plated on to iron?
Answer:
Zinc is plated on to iron to protect it from corrosion and formation of rust.

Chemical Effects of Electric Current Class 8 Extra Questions Short Answer Type 2

Question 1.
Explain the working of a lightning conductor.
Answer:
Lightning conductor is a safety device that protects a tall .building from lightning strike, by providing an easy and alternative path to the heavy charge of lightning. It consists of a long metal rod fixed with side wall of tall building such that its upper end like trishul much above the building while lower end runs deep under earth and joins a large metal plate. Whenever there is lightning, the heavy charge of the lightning is conducted through the metal rod to the earth and the building remains safe.

Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14

Question 2.
What happens at the electrodes connected to the terminals of a battery, when the electrodes are immersed in water and current is passed through the electric circuit?
Answer:
Electrolysis of water takes place and bubbles of oxygen and hydrogen are produced. Oxygen bubbles are formed at positive electrode and hydrogen bubbles are formed at negative electrode.

Question 3.
What happens when an electric current is passed through the conducting solution?
Answer:
The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of gas may be formed, deposits of metal on electrodes may be seen and changes of colour of solution may occur, depending on what solutions and electrodes are used. This is called the chemical effects of the electric current.

Question 4.
Why is disposal of the used conducting solution in the electroplating factories a major concern?
Answer:
In the electroplating factories, the used conducting solution is a hazardous waste which creates a lot of pollution. That is why, the disposal of the used conducting solution is a major concern.

Question 5.
How is copper sulphate solution electrolysed? What are the outcome of this chemical change?
Answer:
When electrical current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate.

The free copper gets drawn to the plate connected to the negative terminal of the battery and thus gets deposited on that plate. From the other plate an equal amount of copper gets dissolved in the solution. This means that copper gets transferred from one plate to another.

Question 6.
What is the benefit of chromium plating on another cheaper materials?
Answer:
Chromium has a shiny appearance. It does not corrode and resists scratches. However, chromium is expensive and it cannot be used to make the whole object. So, the object is made from a cheaper metal and only a coating of chromium over it is done.

Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14

Question 7.
How are tin cans made of? Why are tin cans used for storing food items?
Answer:
Tin cans used for storing food items, are made of by electroplating a layer of tin on to iron. The tin is less reactive as compared to iron. Thus, the food is protected against spoilage.

Chemical Effects of Electric Current Class 8 Extra Questions Long Answer Type

Question 1.
(a) Mention two uses of electroplating.
(b) Explain what happens when electric current is passed through two copper electrodes dipped in copper sulphate solution.
Answer:
(a) (i) Chromium plating is done on various objects like car parts, wheel rims, bath taps, etc.
(ii) Plating of silver or gold is done on less expensive metals by jewellers.
(iii) Iron parts in bridges and automobiles are plated with zinc.
(iv) Tin cans for storing food are made by electroplating tin onto iron. (Any two)

(b) If we pass current through copper sulphate solution with two copper electrodes, copper from anode gets deposited on the copper plate connected to the negative terminal of the battery (Cathode). This is the technique used for the purification of copper.

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