In this page, we are providing Chemical Effects of Electric Current Class 8 Extra Questions and Answers Science Chapter 14 pdf download. NCERT Extra Questions for Class 8 Science Chapter 14 Chemical Effects of Electric Current with Answers will help to score more marks in your CBSE Board Exams.
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 Solutions
Chemical Effects of Electric Current Class 8 Extra Questions Very Short Answer Type
Question 1.
What are good conductors?
Answer:
The substances that conduct electricity through them are called good conductors.
Question 2.
What are insulators or poor conductors?
Answer:
The substances that do not conduct electricity through them are poor conductors or insulators.
Question 3.
Give four examples of conductors.
Answer:
Copper, iron, aluminium and brass.
Question 4.
Give four examples of insulators.
Answer:
Air, wood, rubber and plastic.
Question 5.
Name two metal objects which have a coating of another metal.
Answer:
Handlebars of bicycles, bathroom taps.
Question 6.
What do we get on electrolysis of acidified water?
Answer:
Hydrogen and oxygen gas.
Question 7.
Is air a bad or good conductor?
Answer:
A bad conductor.
Question 8.
Which metal is plated on handle bars of cycles and rim of wheels?
Answer:
Chromium
Question 9.
What is the full form of LED?
Answer:
Light Emitting Diode.
Question 10.
How do we check the electric current?
Answer:
We check the electric current by using a tester.
Question 11.
Which part of an atom is responsible for flow of current?
Answer:
Electron
Question 12.
Why do most liquids conduct electricity?
Answer:
Due to the presence of ions in them, most liquids conduct electricity.
Question 13.
An LED is more efficient device than a bulb. Why?
Answer:
LED is more efficient because it can glow even when a weak or less current flows through it.
Question 14.
Do lemon juice or vinegar conduct electricity?
Answer:
Yes, they conduct electricity.
Question 15.
How is conductivity of liquids tested?
Answer:
By using a tester.
Question 16.
Is water from taps, handpumps, wells and ponds a good conductor?
Answer:
Yes, water from these sources is a good conductor.
Question 17.
What makes distilled water a good conductor?
Answer:
Salts when mixed with distilled water make it a good conductor.
Question 18.
Why is a layer of zinc coated over iron?
Answer:
To prevent iron from corrosion and rust.
Question 19.
Will the solution of sugar in distilled water conduct electricity?
Answer:
No
Question 20.
Why is tin electroplated on iron to make cans used for storing food?
Answer:
Tin is less reactive than iron. Tin coating prevents food from coming in contact with iron and thus pre¬vents it from getting spoiled or corroded.
Question 21.
Why we ifse chromium electroplating on taps and bars of bicycle instead of silver and gold?
Answer:
Silver and gold are very expensive comparatively to chromium.
Question 22.
What type of effect of current do the deposits of metal on electrodes show?
Answer:
Chemical effect
Question 23.
What effect of current does electroplating show?
Answer:
Chemical effect
Question 24.
Which effect of current causes the bulb to glow?
Answer:
Heating effect
Question 25.
Which part of the bulb glows?
Answer:
Filament
Question 26.
Name the three effects of electric current.
Answer:
Heating, magnetic and chemical effect.
Question 27.
How can the magnetic effect of current be checked?
Answer:
By using magnetic compass.
Question 28.
What do we see when the compass needle is brought near a wire in which current is flowing?
Answer:
The needle deflects.
Question 29.
What is electroplating?
Answer:
Deposition of thin layer of a metal over other metal by electrolysis is called electroplating.
Chemical Effects of Electric Current Class 8 Extra Questions Short Answer Type
Question 1.
Define good conductors and poor conductors or insulators.
Answer:
The materials that conduct electricity through them are called good conductors whereas those that do not conduct electricity are called poor conductors or insulators. For example, copper, brass, aluminium, iron, etc., are conductors whereas rubber, plastic, wood, air, etc., are insulators.
Question 2.
How is the conductivity of liquids tested?
Answer:
The free ends of the tester is dipped in the liquid. If the bulb glows, the liquid is said to be a conductor. If not, it is an insulator.
Question 3.
Show with the help of a diagram that lemon juice and vinegar are good conductors of electricity.
Answer:
When the ends of a tester is dipped in lemon juice or vinegar, the bulb glows. This process indicates that lemon juice and vinegar, both, are good conductors of electricity.
Question 4.
What is an LED? Why is it preferred to other type of bulbs?
Answer:
The electric device which is used in the tester instead of bulb is an LED. Its full form is Light Emitting Diode. It is preferred to other bulbs as it can glow even when weak or less current flows through it.
Question 5.
Explain the conductivity of water.
or
Normal water conducts electricity while the pure or distilled water does not. Explain why?
Answer:
Normal water that we get from sources such as taps, handpumps, wells, ponds, etc., is not pure. It may contain several salts dissolved in it naturally. This water is thus good conductor of electricity. The pure or distilled water is free of salts and is a poor conductor.
Question 6.
Give an example of chemical effect of the electric current.
Answer:
The passage of an electric current through a conducting solution causes chemical reactions as a result,
bubbles of a gas are formed, or deposits of metal are seen on electrodes or changes in colour of solution , may occur. These are some of the chemical effects of electric current.
Question 7.
What is electroplating? What are its uses?
Answer:
The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
Electroplating is a very useful process. This is used to make objects appear shiny and resistant to scratches. It prevents corrosion.
Question 8.
What happens when electric current is passed through the copper sulphate solution?
Answer:
When 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.
Question 9.
How does a bulb glow in liquid? Explain.
Answer:
When the liquid between the two ends of a tester allows the electric current to pass through it, then the circuit of the tester becomes complete and the current flows in the circuit of liquid makes the bulb glow. But when the liquid does not allow the electric current to pass through it, then the circuit of the tester is incomplete and the bulb does not glow.
Question 10.
What is the magnetic effect of electricity? Explain.
Answer:
When electric current is passed through a coil or wire, it behaves like a magnet. This is known as mag¬netic effect of current. It depends on amount of current passing through the coil or wire.
Question 11.
Why is magnetic compass needed to test the conduction of electric current?
Answer:
Sometimes, when the current passing through a conductor is so small that filament of the bulb does not get heated up and the bulb does not glow. In this case, we need magnetic compass to test the conduction of current.
Question 12.
What happens when an electric current is passed through a cut potato for a considerable time?
Answer:
When an electric current is passed through a cut potato for a considerable time, greenish blue spot is formed around positive electrode. The chemical effect of the electric current is involved in this process.
Question 13.
Why is chromium used for electroplating? Why the objects have chromium plating are not made of chromium itself?
Answer:
Chromium has a shiny look. It does not get corroded and it resists scratches. Chromium is however expensive and it may not be economical to make the whole object out of it. So the object is made from a cheaper metal and only a coating of chromium is done over it.
Question 14.
Which metals, except chromium, are used for electroplating other metals?
Answer:
Jewellery makers electroplate silver and gold on ornaments of less expensive metals.
Tin cans, used for storing food, are made by electroplating tin onto iron. Tin is less reactive than iron. Hence, food is protected from getting spoilt. Iron used in bridges and automobiles is coated with zinc to protect them from corrosion and formation of rust. •
Question 15.
Current does not flow in a circuit if there is a gap between the two wires. Does it indicate that air is a poor conductor of electricity? Does air never conduct electricity? Explain.
Answer:
Air is a poor conductor of electricity if it is dry but in certain cases like during lightning and when air is moist, air may conduct electricity.
Chemical Effects of Electric Current Class 8 Extra Questions Long Answer Type
Question 1.
On what factors thickness of the electroplated items depend?
Answer:
Thickness of electroplated items depend upon:
- The strength of the current passing through the circuit.
- The concentration of the metal ion in the solution.
- The duration of the time the article has been in the solution.
Question 2.
With the help of a suitable diagram, explain electrolytic refining of copper.
Answer:
To purify copper, a thin plate of pure copper and a thick rod of impure copper are used as electrodes in the acidified solution of CuS04. Pure copper is used as cathode and impure copper is used as anode. When 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 impure copper electrode, an equal amount of copper gets dissolved in the solution. Thus, the loss of copper from solution is restored and the process continues. The impurities are left behind at anode.
Question 3.
Does water conduct electricity? Show with the help of an activity.
or
Show the conductivity of water with the help of an activity.
Answer:
Normal or ordinary water is a good conductor of electricity while distilled water is a bad conductor or insulator. Ordinary water may contain small amount of mineral salts dissolved in it naturally; on the other hand, distilled water is free of salts.
The following activity shows this fact:
About 50 mL of distilled water is taken in a clean and dry beaker. When the tester is dipped into the distilled water, the bulb does not glow which shows that distilled water is a bad conductor of electricity. But when a small amount of common salt is dissolved in distilled water and again tested the bulb glows which shows that distilled water when mixed with salts conduct electricity.
Question 4.
What is electroplating? On which effect of the electric current is it based? Why is it done?
Answer:
The process of depositing or coating a layer of any desired metal on the surface of other material by means of electricity is called electroplating. It is one of the most common applications of chemical effects of electric current.
Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal. The layer of metal deposited has some desired property, which the metal of the object lacks. For example, chromium plating is done on many objects to make them shiny and at¬tractive.
Question 5.
What are the advantages and disadvantages of electroplating?
Answer:
Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of different metal. The advantages and disadvantages of electroplating are:
Advantages:
- It protects the metals from being corroded.
- It prevents the rusting of metals.
- It makes cheap and dull metals shiny and attractive.
- It can make more reactive metals like iron less reactive.
- Chromium coating on metals give lustre to objects.
Disadvantages
- Pollutants from electroplating industries are very harmful. Some chemicals are very lethal for both human and animals.
- It is an expensive process.
Chemical Effects of Electric Current Class 8 Extra Questions HOTS
Question 1.
Why electric fires are extinguished with either using C02 extinguisher or mud but not water?
Answer:
As water is a good conductor of electricity so it can cause electrocution. Hence, water is avoided in ex¬tinguishing electric fires.
Question 2.
Why do you think electroplated jewelleries are in demand?
Answer:
Electroplated jewelleries are in demand because firstly, they are as shiny and attractive as real jewelleries. They are light-weighted and cost effective. Secondly, one feels free to wear it because of the growing problem of snatching and theft.
Question 3.
Do distilled water conduct electricity? What will happen if we add sugar to it and then salt to it? Explain.
Answer:
No, distilled water do not conduct electricity. If we add sugar to distilled water, then also it will not conduct electricity because sugar do not dissociates into ions. But on adding salt, it will conduct electricity because aqueous salt solution is a good conductor of electricity.
Question 4.
Suppose you want to deposit silver on an iron spoon using silver nitrate as electrolyte. Which terminal of the battery you should connect the spoon? What material should the other electrode be made of?
Answer:
Silver ion is positively charge, so the spoon must be connected to negative terminal to deposit silver on it. The other electrode should be made of silver.
Question 5.
Why potato turns green on passing current? Around which terminal greenish patch is observed?
Answer:
Potato turns green due to chemical effect of current. Around positive terminal greenish patch in potato is observed.
Chemical Effects of Electric Current Class 8 Extra Questions Value Based (VBQs)
Question 1.
Yakub made an circuit as shown in the figure. He observed that the bulb did not glow but on bringing a compass needle near it shows deflection.
He was quite confused that if current is flowing through the circuit then why the bulb is not glowing. Meanwhile his friend Sourav arrived and suggested him to add one more cell in the circuit. The bulb, then started glowing.
(a) Define a circuit.
(b) What does the deflection of a compass needle shows?
(c) Why the bulb did not glow in the first case but glow in the second case?
(d) What value of Sourav is shown here?
Answer:
(a) Circuit is a closed path through which an electric current flows.
(b) Deflection of compass needle shows that the current is flowing in the circuit. It is magnetic effect of
current.
(c) The current flowing through the circuit in first case was too low to make the bulb glow but on add-ing a cell in the second case makes the bulb glow.
(d) Sourav is an intelligent, helpful, analytical and with scientific aptitude.
Question 2.
While demonstrating an experiment to show whether the given liquid conduct electricity or not to class VIII students, teacher reminded everybody that one should not conduct experiment with the electric supply from the mains or a generator or an inverter. They should use electric cells for the activity.
(a) Do liquids conduct electricity?
(b) Why we should not use electric source from mains generator or an inverter?
(c) What values do we get from this?
Answer:
(a) Yes, liquids which are solutions of acids, bases and salts conduct electricity. Other liquids such as oil, alcohol, sugar solution and pure water do not conduct electricity.
(b) Current flowing from mains, generator or an inverter is very large. So to avoid the chances of elec-trocution and short-circuit we must use cells for experiments.
(c) We get awareness of not using main electric supply and precaution to be followed while doing experiment.