These AP 8th Class Physics Important Questions and 8th Lesson Chemical Effects of Electric Current Class 8 Extra Questions will help students prepare well for the exams.
Class 8 Science Chemical Effects of Electric Current Extra Questions
Chemical Effects of Electric Current Class 8 Important Questions
Question 1.
Why it is dangerous to touch an electrical appliance with wet hands ?
Answer:
It is dangerous to touch an electrical appliance with wet hands because the electricity may pass through our body and causes electrical shock.
Question 2.
What are good conductors of electricity ?
Answer:
The materials, which allow the electric current to pass through them, are good conductors of electricity.
Question 3.
What are poor conductors of electricity ?
Answer:
The materials, which do not allow the electric current to pass through them easily, are poor conductors of electricity.
Question 4.
Give examples of good conductors of electricity.
Answer:
Examples of good conductors : Metals such as copper and aluminium are good conductors.
Question 5.
Give examples of poor conductors of electricity.
Answer:
Examples of poor conductors of electricity: Rubber, plastic and wood.
Question 6.
Do liquids also conduct electricity ?
Answer:
Yes, some liquids also conduct electricity.
Question 7.
Sometimes the bulb of the tester does not glow even tested with conductors. Why?
Answer:
If the; current through a circuit is too weak, the filament does not get heated sufficiently and it does not glow.
Question 8.
What happens to a compass needle kept nearby when current flows in a wire?
Answer:
Even if the current is small, a compass needle is kept nearby when current flows in a wire the deflection of the magnetic needle can be seen.
Question 9.
Write a precaution to be taken while doing the activity to test the tester.
Answer:
While checking a tester, do not join its free ends for more them a few seconds. Otherwise, the cells of the battery will drain very quickly.
Question 10.
Adding which substance make pure water a good conductor ?
Answer:
Adding common salt to distilled water makes it a good conductor.
Question 11.
You have learned some effects of electric current. Can you list these effects ?
Answer:
The heat effect of electricity, light effect of electricity, magnetic effect of electricity, sound effect of electricity, etc., are some of the effects of electricity.
Question 12.
What gases will release if current pass through the water by using electrodes ?
Answer:
Oxygen and hydrogen will release if current pass through the water by using electrodes.
Question 13.
At which terminal greenish blue spot will be formed when electricity is passed through a potato by using electrodes ?
Answer:
At the positive terminal greenish blue spot will be formed when electricity is passed through a potato by using electrodes.
Question 14.
What is electroplating ?
Answer:
The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
Question 15.
Write one example of the chemical effect of electricity.
Answer:
Electroplating is an example of the chemical effect of electricity.
Question 16.
How does electroplating industry cause to pollution ?
Answer:
In the electroplating factories the used conducting solutions are caused to pollution.
Question 17.
Write different types of testers to heat conductivity of electricity in liquids.
Answer:
- A circuit tester with a bulb.
- A circuit tester with an LED.
- A circuit tester with a magnetic compass.
Question 18.
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.
Question 19.
What happens if we connect a carbon rod in the place of the copper plate which was connected to the negative terminal of the battery in the electroplating experiment with copper sulphate ?
Answer:
A coating of copper will obtain on the carbon rod.
Question 20.
Why do we use LEDs as indicators in electrical appliances ?
Answer:
LEDs glow even With a very small current passing through them. So they are used as indicators in electrical appliances like mobile phones, televisions, transformers, etc. to indicate whether the device is working or not.
Chemical Effects of Electric Current Extra Questions
Question 1.
Give examples of the poor conductors and good conductors in liquids.
Answer:
Poor conductors : Sugar solution, distilled water, honey, coconut oil etc.
Good conductors : Sea water, milk, vinegar, lemon juice, coconut water, acids, bases, salt solutions etc.
Question 2.
Write different types of testers to test the conductivity of electricity in liquids, which tester is best?
Answer:
Different types of testers to test the conductivity of electricity in liquids :
- A circuit tester with a bulb
- A circuit tester with an LED
- A circuit tester with a magnetic compass.
- A circuit tester with a magnetic compass is best as it can test even small currents.
Question 3.
Does a poor conductor conduct electricity ? If so, give an example.
Answer:
- Yes, poor conductors can also allow electricity under certain conditions.
- For example, lightning is caused by conducting of electricity through the air, a poor conductor.
Question 4.
Why all the materials are classified as good conductors and poor conductors instead
of classified as conductors and insulators ?
Answer:
- Actually, under certain conditions most materials can conduct.
- That is why it is preferable to classify materials as good conductors and poor conductors instead of classifying them as conductors and insulators.
Question 5.
Can we handle electrical appliances with wet hands or while standing on a wet floor ? Why ?
Answer:
- Small amounts of mineral salts present naturally in water make water a good conductor.
- So, we should never handle electrical appliances with wet hands or while standing on a wet floor.
Question 6.
What are the substances which, when dissolved in distilled water, make it conducting of electricity ?
Answer:
The dissolving of acids, bases and salts in the distilled water makes it conducting of electricity.
For examples : Hydrochloric acid, caustic soda, sodium hydroxide etc.
Question 7.
What changes do you observe in the given activity shown in the figure? What is the cause for it ?
Answer:
- We can notice gas bubbles near the electrodes.
- Deposits of metal may be seen on electrodes.
- Changes in the colour of solutions may occur.
- The change taking place in the solution is a chemical change.
- The passage of an electric current through a conducting solution causes chemical reactions.
- As a result, bubbles of a gas may be formed on the electrodes.
- The reaction would depend on what solution and electrodes are used.
Question 8.
What will happen if electrodes were immersed in water and a current was passed?
(OR)
Write about the experiment of separation of gases from the water conducted by William Nicholson.
Answer:
- In 1800, a British chemist, William Nicholson (1753 – 1815), had shown that if electrodes were immersed in water and a current was passed, bubbles of oxygen and hydrogen were produced.
- Oxygen bubbles formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles formed on the other electrode.
Question 9.
What happens at the electrodes when current is passed through the copper sulphate solution ? Explain.
Answer:
- 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.
- Thus, the loss of copper from the solution is restored and the process continues. This means that copper gets transferred from one electrode to the other.
Question 10.
Write any two situations where you observe electroplating.
Answer:
- I observed that a brand-new bicycle has shiny handle bar and wheel rims. However, if these are accidentally scratched, the shiny coating comes off revealing a not-so- shiny surface beneath.
- Generally, women use ornaments, which appear to be made of gold. However, with repeated use, the gold coating wears off, revealing silver or some other metal beneath.
- In both these cases, metal has a coating of another metal.
Question 11.
How is electroplating with chromium metal useful ?
Answer:
- Chromium has a shiny appearance. It does not corrode. It resists scratches.
- However, chromium is expensive and it may not be economical to make the whole object out of chromium.
- So, the object is made from a cheaper metal and only a coating of chromium over it is deposited.
- For example, chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others.
Question 12.
How is electroplating with tin metal is useful ?
(OR)
Where are tin cans used ? Why ?
Answer:
- Tin is less reactive than iron.
- Thus, food does not come into contact with iron and is protected from getting spoilt.
- Tin cans, psed for storing food, are made by electroplating tin onto iron.
Question 13.
Where is electroplating with zinc metal used ? Why ?
Answer:
- Iron is used in bridges and automobiles to provide strength.
- However, iron tends to corrode and rust.
- So, a coating of zinc is deposited on iron to protect it from corrosion and formation of rust.
Question 14.
How is silver or gold plating useful ?
Answer:
- Gold and silver are more expensive metals.
- So, jewellery makers electroplate silver and gold on less expensive metals.
- The silver or gold plating jewellery looks like silver or gold jewellery and available with less cost.
Question 15.
Write an alternative device to check even weak electric current flow.
(OR)
Write the use of LED tester.
Answer:
- We may use an LED in place of the electric bulb in the tester.
- 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.
Question 16.
How does an electric tester work in liquids ?
Answer:
- When the liquid between the two ends of the tester allows the electric current to pass, the circuit of the tester becomes complete.
- The current flows in the circuit and the bulb glows.
- When the liquid does not allow the electric current to pass, the circuit of the tester is not complete and the bulb does not glow.
Question 17.
Why chromium is used to electroplate on most of the iron articles ?
Answer:
- Chromium has a shiny appearance.
- It does not corrode.
- It resists scratches.
Question 18.
What are the requirements for fine coating in electroplating process ?
Answer:
- The object to be electroplated should be free from greasy matter.
- The surface of the article should be rough so that the metal deposited sticks permanently.
- The concentration of the electrolyte should be so adjusted as to get smooth coating.
- Current must be the same throughout.
Extra Questions of Chemical Effects of Electric Current Class 8
Question 1.
How do you classify the materials according to their conductivity ? Explain.
Answer:
- Materials are classified into two types according to their conductivity.
- They are good conductors and poor conductors.
- The materials, which allow the electric current to pass through them, are good conductors of electricity.
- Examples of good conductors : Metals such as copper and aluminium are good conductors.
- The materials, which do not allow the electric current to pass through them easily, are poor conductors of electricity.
- Examples of poor conductors of electricity : Rubber, plastic and wood.
Question 2.
What is electroplating? Write three applications of it.
Answer:
- The process of depositing a layer of any desired metal on another material by means of electricity is Called electroplating.
Applications: - Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal.
- Jewellery makers electroplate silver and gold on less expensive metals.
- Tin cans, used for storing food, are made by electroplating tin onto iron.
- Zinc coated iron is used in bridges and automobiles to provide strength and rust proof.
- Chromium plating is done over iron of many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others.
Question 3.
Draw the diagram of a tester to test a liquid for conductivity.
Answer:
Question 4.
Draw the diagram of a simple circuit showing electroplating.
Answer:
Question 5.
Draw the diagram of a simple circuit of a tester with magnetic compass.
Answer:
Question 6.
Draw the diagram of a simple circuit showing passing of electricity through water.
Answer:
Question 7.
Draw the diagram of a simple circuit showing testing of a potato.
Answer:
Question 8.
Explain the uses of the electroplating process in our daily life.
Answer:
- 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 such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others.
- Chromium has a shiny appearance. It does not corrode. It resists scratches.
- However, chromium is expensive and it may not be economical to make the whole object out of chromium.
- So, the object is made from a cheaper metal and only a coating of chromium over it is deposited.
- Jewellery makers electroplatesilver 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.
- Iron is used in bridges and automobiles to provide strength.
- However, iron tends to corrode and rust.
- So, a coating of zinc is deposited on iron to protect it from corrosion and formation of rust.
Question 9.
How do you test whether some fruits and vegetables conduct electricity or not ?
(OR)
What do you observe when electricity passed through a potato by using electrodes?
Answer:
Aim : to test whether some fruits and vegetables conduct electricity or not.
- Cut a potato into two halves and inserted the copper wires of a tester into it.
- Leave it for some time.
- Observe after half an hour.
- There was a greenish blue spot on the potato around one wire whereas there was no such spot around the other wire.
- We can also find that it was always the wire connected to the positive terminal, which had a greenish blue spot around it.