Here we are providing Online Education Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14 was designed by subject expert teachers. https://ncertmcq.com/extra-questions-for-class-8-science/
Online Education for Class 8 Science Chapter 14 Extra Questions and Answers Chemical Effects of Electric Current
Chemical Effects Of Electric Current Class 8 Questions And Answers Question 1.
Most liquids which conduct electricity are solutions of ……………… and …………. .
Answer:
salt, water.
Chemical Effects Of Electric Current Class 8 Question Answer 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.
Class 8 Science Chapter 14 Question Answer 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.
Chemical Effects Of Electric Current Class 8 Pdf Questions And Answers Question 4.
Is air an insulator under all conditions?
Answer:
Only dry air is an insulator, but damp air is a conductor.
Chemical Effect Of Electric Current Question Answer Question 5.
Is salt solution a conductor?
Answer:
Yes, it is.
Class 8 Science Chapter 14 Question 6.
Can there be made a coating of one metal on another?
Answer:
Yes, by electroplating, it can be done.
Chemical Effect Of Electric Current Class 8 Question Answer Question 7.
In electroplating, what effect of current is observed?
Answer:
Chemical effect.
Chemical Effects Of Electric Current Class 8 Solutions 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.
Chapter 14 Science Class 8 Question Answer 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.
Chapter 14 Science Class 8 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.
Class 8 Chapter 14 Science Question 11.
Define conductors.
Answer:
Materials which allow electric current to pass through them are called conductors, e.g., aluminium, copper, etc.
Class 8 Science Chapter 14 Short Question Answer Question 12.
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.
Class 8 Science Ch 14 Question Answer Question 13.
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.
Class 8 Science Chapter 14 Questions And Answers Question 14.
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.
Chemical Effects Of Electric Current Class 8 Question 15.
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.
Question 16.
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 17.
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 18.
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 19.
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 20.
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 21.
Why is zinc plated on to iron?
Answer:
Zinc is plated onto iron to protect it from corrosion and formation of rust.
Question 22.
Explain the working of a lightning conductor.
Answer:
Lightning conductor is a safety device that protects a tall .building from lightning strikes, 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.
Question 23.
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 24.
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 25.
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 26.
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 27.
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.
Question 28.
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 onto iron. The tin is less reactive as compared to iron. Thus, the food is protected against spoilage.
Question 29.
(a) Mention two uses of electro-plating.
(b) Explain what happens when electric current is passed through two copper electrodes dipped in copper sulphate solution.
Answer:
(a)
- Chromium plating is done on various objects like car parts, wheel rims, bath taps, etc.
- Plating of silver or gold is done on less expensive metals “by jewellers.
- Iron parts in bridges and automobiles are plated with zinc.
- 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.
Multiple Choice Questions (MCQs)
1. Electroscope is a device to detect
(a) current
(b) charges
(c) earthquake
(d) rainfall
Answer:
(b) charges.