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Science Question Answer (3 Marks)

Chemical effects of electric current · Maharashtra Board STD 8 (MSBSHSE - Semi English Medium). 14 questions.

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Question Answer (3 Marks)

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14 questions · timed · auto-graded

Question 13 Marks
What is meant by electroplating? What is the purpose of electroplating?
Answer
The process of coating of a layer of any metal over other metal is called electroplating.
The purpose of electroplating is to provide the shiny appearance, rust free metal surface etc.
Example:
  1. Chromium plating is done on metals body parts of cars, bikes, cycles, etc.
  2. Gold and silver plating is done on the artificial jewelry.
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Question 23 Marks
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 will you observe when an electric current is passed through this set-up for a considerable time?
Answer
The carbon is a non-metal which is more reactive than copper. When, an electric current is passed through this set-up for a considerable time, then carbon replaces copper ions from solutions and they deposit on the negative electrode. Thus, a red-brown layer of copper metal will be deposited on the carbon rod connected to the negative terminal of the battery.
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Question 33 Marks
In case of a fire, before the firemen use the water hoses to throw water to douse fire, they shut off the electricity supply for the area. Explain why this is done.
Answer
In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area because water may conduct electricity. If the electrical supply for the area is not shut off and water is poured over electrical appliances, then electricity may pass through water and harm the firemen.
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Question 43 Marks
When the free ends of a conductivity tester (made by using a battery connected to a wire wound around a compass) are dipped into a solution, the magnetic needle shows deflection. Can you give the reason for this deflection.
Answer
Because the free ends of a conductivity tester are dipped into a conducting solution then, it behaves like a current carrying wire and a current carrying wire behaves as a magnet because it produces magnetic field around it. And, due to this there is deflection in the compass.
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Question 53 Marks
Why does a brand new bicycle have shining handlebar and wheel rims? What will happen if these are accidently scratched?
Answer
The shining coating is done on the metal by electroplating. When these are accidently scratched then, the metal will be rusted due to presence of air. So, by some metal these are coated so as to avoid rusting of iron mainly used to build the handlebars and wheel rims.
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Question 63 Marks
Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Answer
No, it is very risky and unsafe for the electrician to carry out electrical repairs outdoors during heavy downpour because rain water is conducting in nature as it contains dissolved salts. The electrician may get electrical shocks while working outdoors during rain as water may conduct electricity.
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Question 73 Marks
For electroplating copper on an iron object, which terminal of the battery (positive or negative) is connected to the iron object? Also name the electrolyte you will use for this purpose.
Answer
In the process of electroplating, the metal to be electroplated is taken as cathode and the one used for coating is chosen as the anode. And, we know, anode is positive terminal and the cathode is negative terminal. Thus, negative terminal will be connected to the iron object.
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Question 83 Marks
When an electric current is passed through a cut potato for a considerable time, a coloured spot is formed around one of the electrodes:
  1. What is the colour of the spot?
  2. Around which electrode (positive or negative electrode) the coloured spot is formed?
  3. Which effect of electric current is involved in this case?
Answer
  1. The spot color is Greenish blue.
  2. The coloured spot is formed around the positive electrode.
  3. This is known as Chemical effect.
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Question 93 Marks
What is electrolysis? Explain why, in the electrolysis of water, 'acidified water' is used.
Answer
Electrolysis is the process of dissociation of water molecules into H + and OH – ions. When electric current is passed through it in a conducting state. Because water does not have much higher concentration of ions. Dilute sulphuric acid is added to increase the concentration of ions in the water.
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Question 103 Marks
What is meant by the chemical effect of electric current? Explain with the help of an example.
Answer
When electric current passes through any conducting solution, then chemical reactions take place inside the conducting solution. This effect is called as chemical effect of electric current.
Example:
electroplating. The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
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Question 113 Marks
In the process of purification of copper metal, a thin plate of pure copper and a thick rod of impure copper are used as electrodes, and a metal salt solution is used as an electrolyte:
  1. Which electrode is connected to the positive terminal of the battery?
  2. Which electrode is connected to the negative terminal of the battery?
  3. Which metal salt solution is taken as electrolyte?
Answer
  1. Thick rod of impure copper is connected to the positive terminal of the battery.
  2. Thin plate of pure copper is connected to the negative terminal of the battery.
  3. Copper sulphate solution is taken as electrolyte.
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Question 123 Marks
State some of the characteristics of chemical changes brought about by the chemical effect of electric current.
Answer
The some of the characteristics of chemical changes brought about by the chemical effect of electric current:
  1. The solution colour changes might take place.
  2. The bubbles evolve through the solution.
  3. The chemical deposition of one metal and replacement of the other metal.
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Question 133 Marks
A student staying in a coastal region tests the drinking water and also the sea water 'With a circuit in which a part of the connecting wire is wound around a matchbox containing compass. He finds that the compass needle deflects more in the case of sea water. Can you explain the reason?
Answer
Sea water is a better conductor because it contains sodium and chloride ions in large amounts. These ions make the solution conducting and thus, sea water is considered better conductor than the drinking water which does not contain ions. The ions of drinking water are removed while removed while purifying it.
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Question 143 Marks
Name three types of substances in which an electric current can produce a chemical effect.
Answer
The three types of substances in which an electric current can produce a chemical effect.
  1. Water.
  2. Copper sulphate.
  3. Vinegar.
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Question Answer (3 Marks) - Science STD 8 Questions - Vidyadip