Chemical Effects of Electric Current Class 8 Science Extra Questions and Answers
Chemical Effects of Electric Current Class 8 Science Chapter 14 Extra Questions and Answers are provided here. We prepared these extra questions based on the latest NCERT Class 8 Science Book. CBSE Class 8 Science Chapter 14 Chemical Effects of Electric Current Extra Questions will help you to properly understand a particular concept of the chapter.
Class 8 Science Chapter 14 Chemical Effects of Electric Current Extra Questions
Very Short Answer Type Question
Question 1: Which metal is electroplated on bathroom fittings?
Answer: Chromium is usually electroplated on bathroom fittings.
Question 2: Name any one metal which is purified by using the chemical effect of current (or electrolysis).
Question 3: Do liquids also conduct electricity?
Answer: No, some liquids are good conductors of electricity and some are poor conductors.
Question 4: Give one example of the chemical effect of electric current.
Answer: Bubbles of gases are formed when an electric current is passed through acidified water.
Question 5: How is water decomposed into hydrogen and oxygen?
Answer: Water is decomposed into hydrogen and oxygen by passing electric current through it.
Question 6: Name some liquids which conduct electricity.
Answer: Liquids such as vinegar, lemon juice, tap water, rain water and sea water conduct electricity.
Question 7: Name some liquids which do not conduct electricity.
Answer: Liquids such as water, milk, vegetable oil and honey do not conduct electricity.
Question 8: State whether vinegar and lemon juice will conduct electricity or not.
Answer: Though vinegar and lemon juice conduct electricity but they are weak conductors of electricity.
Question 11: 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 12: What happens to a compass needle kept nearby when current flows in a wire?
Answer: Even if the current is small, the deflection of the magnetic needle can be seen.
Question 13: Name a device which glows even when a weak electric current passes through it.
Answer: LED (Light Emitting Diodes) glows even when a weak electric current flows through it.
Question 14: Which is the polluting waste generated by electroplating factories?
Answer: The conducting solution used in the electroplating process is the polluting waste generated by electroplating factories.
Question 15: What is the advantage of using LED in testing the electrical conductivity of liquids?
Answer: The advantage of using LED in testing the electrical conductivity of liquids is that it glows even when a weak electric current flows through it.
Question 16: Does pure water conduct electricity? If not, what can we do to make it conducting?
Answer: Pure water is free of salts and is a poor conductor. We can add some common salt in pure water to make it conducting.
Question 17: Name two metals which are usually electroplated on cheaper metals for making jewelry (or ornaments).
Answer: Silver and gold are usually electroplated on cheaper metals for making jewelry (or ornaments).
Question 18: Which effect of electric current is utilized for detecting the flow of current through a solution when a compass is used?
Answer: Magnetic effect of electric current is utilized for detecting the flow of current through a solution when a compass is used.
Question 19: When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Answer: The deflection in magnetic needle shows that the circuit is complete and the solution conducts electricity.
Question 20: Which metal is usually electroplated on car parts such as bumpers and bicycle handlebars made of steel?
Answer: Chromium is usually electroplated on car parts such as bumpers and bicycle handlebars made of steel.
Short Answer Type Questions
Question 1: Which metal is electroplated on iron for making cans and why?
Answer: Tin is electroplated on iron for making cans because tin is less reactive than iron. Thus, food does not come into contact with iron and is protected from getting spoilt.
Question 2: Why is the current in the circuit weak?
Answer: Though a material may conduct electricity, it may not conduct it as easily as a metal. As a result, the circuit of the tester may be complete and yet the current through it may be too weak to make the bulb glow.
Question 3: Why do brand new cycles have shiny handlebars and wheel rims what will happen if these are scratched?
Answer: A brand new bicycle has shiny handlebar and wheel rims. However, if these are accidentally scratched, the shiny coating comes off revealing a not so shiny surface beneath.
Question 4: Why is it dangerous to touch a working electrical appliance with wet hands?
Answer: It is dangerous to touch a working electrical appliance with wet hands because the tap water is a good conductor of electricity due to which it may conduct electric current and gives us an electric shock.
Question 5: Write two common application of the chemical effect of electric current.
Answer: Two common application of the chemical effect of electric current are:
- Electroplating of metals
- Purification of metals
Question 6: For electroplating copper on an iron object, which terminal of the battery (positive or negative) is connected to the iron object?
Answer: In the process of electroplating, the metal to be electroplated is taken as cathode (negative) and the one used for coating is chosen as the anode (positive). Thus, negative terminal will be connected to the iron object.
Question 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.
Answer: Water is a conductor of electricity, so if the electricity supply is not cut off and firemen come in contact with wet electric switches, electric wires and other electrical appliances, they may get electrocuted.
Question 8: Why the bulb glows when the electric current passes through it?
Answer: Due to the heating effect of current, the filament of the bulb gets heated to a high temperature and it starts glowing. However, if the current through a circuit is too weak, the filament does not get heated sufficiently and it does not glow.
Question 9: What is meant by the chemical effect of electric current? Give an example.
Ans. The passage of an electric current through a conducting liquid causes chemical reactions. The resulting effects are called chemical effects of currents. Example – Deposit of metal formed when electric current is passed through copper sulphate solution (during electroplating).
Question 10: Which properties of chromium metal make it suitable for electroplating?
Answer: The properties of chromium metal that make it suitable for electroplating are:
- It has a shiny appearance.
- It does not corrode.
- It resists scratches.
Question 11: Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Answer: It is not safe for the electrician to carry out electrical repairs outdoors during heavy downpour because rainwater being a conductor of electricity may cause electrocution of the electrician.
Question 12: A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Answer: The compass needle deflects more in the case of seawater because due to the presence of a large amount of dissolved salts in it, sea water is a much better conductor of electricity than drinking water.
Question 13: What are the chemical effects of electric current?
Answer: When an electric current flows through a conducting solution, it causes following chemical change:
- Bubbles of gas or gases may be formed on the electrodes.
- Deposits of metals may form on electrodes.
- Changes in colour of solutions may occur.
Long Answer Type Questions
Question 1: What happens when electric current is passed through acidified water?
Answer: When electrodes are immersed in water, and a current is passed through acidified water, then oxygen gas is formed at the positive electrode which is connected to the positive terminal of the battery and hydrogen gas is formed at the negative electrode which is connected to the negative terminal of the battery.
Question 2: Tap water conducts electricity whereas distilled water does not. Give reason.
Answer: Distilled water is a poor conductor of electricity because it does not contain any dissolved salts in it which can provide it ions to conduct electricity. The distilled water becomes a good conductor of electricity on dissolving a little salt in it. The water that we get from taps is not pure. It may contain several salts dissolved in it. This water is thus a good conductor of electricity.
Question 3: Why is electroplating useful?
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.
Question 4: 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?
Answer: Rainwater is said to be pure water. But when rainwater falls to the earth through the atmosphere, it dissolves acidic gases such as carbon dioxide, sulphur dioxide and nitrogen oxides to form acids such as carbonic acid, sulphuric acid and nitric acid. Due to presence of acids in it, rainwater becomes a conductor of electricity.
Question 5: Prepare a list of objects around you that are electroplated.
Answer: Examples of electroplating
- Chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others.
- Jewellery makers electroplate silver and gold on less expensive metals.
- Tin cans, used for storing food, are made by electroplating tin onto iron.
- A coating of zinc is deposited on iron to protect it from corrosion and formation of rust.
Question 6: The process that you saw in Activity 14.7 is used for purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of battery and why?
Answer: A thick rod of impure copper should be connected to the positive terminal of the battery. A thin plate of pure copper should be connected to the negative terminal of the battery. On passing electric current, the metal dissolves from the impure anode and goes into the electrolyte solution. The positively charged ions of metals present in their molten compounds are attracted by the negatively charged electrode.
Question 7: A beaker contains an acidified copper sulphate solution. A copper plate and a carbon rod are kept in this copper sulphate solution. The copper plate is connected to the positive terminal of a battery whereas the carbon rod is connected to the negative terminal of the battery. What happens when electric current is passed through 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. 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 keeps going. This means that copper gets transferred from one electrode to the other.
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