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Ncert Exemplar Solutions Class 8 Science Chemical Effects of Electric Current
Welcome to NCTB Solutions. Here with this post we are going to help 8th class students for the Solutions of NCERT Exemplar Class 8 Science Book, Unit 14, Chemical Effects of Electric Current. Here students can easily find step by step solutions of all the problems for Chemical Effects of Electric Current, Also here our Science teacher’s are solved all the questions with easily understandable language with proper guidance so that all the students can understand easily.
Chemical Effects of Electric Current all Question Solutions :
Multiple Choice Questions :
Question no – (1)
An electric current can produce
Answer :
Correct option – (d)
An electric current can produce chemical, heating, and magnetic effects.
Question no – (2)
Boojho and Paheli performed experiments taking similar bulbs and cells but two different solutions A and B as shown in Fig. 14.1.
Answer :
Correct option – (a)
Higher current is flowing through the circuit in setup A.
Question no – (3)
Boojho’s uncle has set up an electroplating factory near his village. He should dispose off the waste of the factory
Answer :
Correct option – (d)
He should dispose off the waste of the factory according to the disposal guidelines of the local authority.
Question no – (4)
When electric current is passed through a conducting solution, there is a change of colour of the solution. This indicates
Answer :
Correct option – (a)
This indicates the chemical effect of current.
Question no – (5)
Which one of the following solutions will not conduct electricity?
Answer :
Correct option – (d)
Vegetable oil will not conduct electricity.
Question no – (6)
Which of the following metals is used in electroplating to make objects appear shining?
Answer :
Correct option – (c)
Chromium is used in electroplating to make objects appear shining.
Question no – (7)
Which of the following solutions will not make the bulb in Fig 14.2 glow?
Answer :
Correct option – (d)
Sugar solution in diluted water will not make the bulb in Fig 14.2 glow.
Very Short Answer Questions :
Question no – (8)
Answer :
(a) The object to be electroplated is taken as Cathode electrode.
(b) One of the most common applications of chemical effect of electric current is Electroplating.
(c) Small amount of a mineral salt present naturally in water makes it a Good Conductor of electricity.
(d) Electroplating of Chromium is done on objects like water taps and cycle bell to give them a shiny appearance.
Question no – (9)
Answer :
A layer of zinc is coated over iron to protect it from rusting and corrosion.
Question no – (10)
Answer :
The solution of sugar and distilled water does not conducts electricity because most liquid which conduct electricity are acid, basic or contains salt in it.
Question no – (11)
Answer :
The heating effect of current is responsible for the glow of the electric bulb. The electricity passing in the circuit heats up the bulb and so it glows.
Short Answer Questions :
Question no – (12)
Answer :
On adding one more cell the in the circuit the potential difference between the terminal increases, so a sufficient amount of electricity passes through the circuit which glows up the bulb.
Question no – (13)
Answer :
The liquid A was a very good conductor of electricity so it allows electricity to pass through it easily, so the electric bulb in the circuit glows with ease. On the other hand liquid B was a weak conductor so only a little bit of electricity passes in the circuit which is sufficient enough to glow a led but not a bulb.
Question no – (15)
Answer :
The can that are used to store food are electroplated with tin. Tin are less reactive than iron so when the food comes in contact with the iron it does not react with the tin, so the food healthy to eat.
Question no – (16)
Answer :
The circuit A shows the correct observation. The wire which is connected to the positive terminal of cell makes the potato to turn greenish blue at the spot where the wire is poked.
Question no – (17)
Answer :
• Piece of Coal :
No, coal is a bad conductor of electricity so it won’t glow.
• Iron nail :
Yes, the bulb will glow as iron is a good conductor of electricity.
• Eraser :
No, it won’t grow because an eraser is made up of rubber which is a bad conductor of electricity.
• Steel Spoon :
Yes, it will glow because the spoon is made up of iron which is a great conductor of electricity.
Long Answer Questions :
Question no – (18)
Answer :
These three observations that can be seen when an electric current is passed through a conducting solution are :
• The solution may heat up because of the heating effect of the electric current
• Due to chemical reaction taking place in the solution bubbles of gases might be seen emitting from the electrodes
• The solution may change its colour depending on the chemical changes taking place in the solution.
Question no – (19)
Answer :
Yes, the copper will still be deposited on the carbon rod. When the electric current is passed through the solution, the solution dissociates into copper and sulphur. The copper from the solution as well as the positive electrode gets deposited on the negative electrode, that is the copper rod.
Question no – (20)
Answer :
(I) The plate A must be the impure copper plate connected to the positive terminal.
(II) The plate B must be the other copper plate that needs to be electroplated or purified.
(III) The solution must be a copper sulphate solution so that it can dissociates into copper and sulphur.
In purification process as the electricity is passed through the solution, the impure copper plate and the solution releases copper in the solution that gets deposited on the negative copper plate. This result in the addition of a layer of pure copper on the electrode.
Question no – (21)
Answer :
Since in the given circuit the current does not flows in the circuit, it implies one thing that is air is not a good conductor of electricity. But often times air becomes a good conductor of electricity when the moisture in the air increases to a sufficient amount to pass electricity, like in thunderstorms.
Question no – (22)
Answer :
There will be significant difference in the observation if lemon juice is not added in the liquid. We will see that there will be no chemical effect of current such as forming of bubbles as there is no electricity passing through the water since adding lemon juice increases the conductivity of the water by releasing acids, salts and minerals in the water.
Question no – (23)
Answer :
(i) The defection in the magnetic compass simply shows that an electric is flowing through the circuit.
(ii) The bulb in figure A is not glowing because the liquid in the apparatus is not a good conductor of electricity. So a weak electric current is passing through the bulb which does not heats up the electric bulb to glow.
(iii) If we increase the number of turns around the magnetic compass then the magnetic effect of the current around the compass will increase this in will turn make it deflect much more.
(iv) If we increase the number of coils in the circuit then a much larger electric current will flow through the circuit which will make the needle of the compass deflect a little bit further.
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