Chemical Effects Of Electric Current
Class 8th Science CBSE Solution
- Fill in the blanks.(a) Most liquids that conduct electricity are solutions of__________,…
- When the free ends of a tester are dipped into a solution, the magnetic needle shows…
- Name three liquids, which when tested in the manner shown in Fig. 14.9, may cause the…
- The bulb does not glow in the setup shown in Fig. 14.10. List the possible reasons.…
- A tester is used to check the conduction of electricity through two liquids, labelled A…
- Does pure water conduct electricity? If not, what can we do to make it conducting?…
- In case of a fire, before the firemen use the water hoses, they shut off the main…
- A child staying in a coastal region tests the drinking water and also the seawater with…
- Is it safe for the electrician to carry out electrical repairs outdoors during heavy…
- Paheli had heard that rain water is as good as distilled water. So, she collected some…
- Prepare a list of objects around you that are electroplated.
- The process that you saw in Activity 14.7 is used for purification of copper. A thin plate…
Exercises
Question 1.Fill in the blanks.
(a) Most liquids that conduct electricity are solutions of__________, __________ and_________.
(b) The passage of an electric current through a solution causes ___________ effects.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ___________ terminal of the battery.
(d) The process of depositing a layer of any desired metal on another material by means of electricity is called _______.
Answer:
(a) Most liquids that conduct electricity are solutions of acids, bases, and salts.
Explanation: Acids, bases, and salts when dissolved in water give ions. These ions conduct electricity.
(b) The passage of an electric current through a solution causes chemical effects.
Explanation: Whenever electric current passes through a conducting liquid, then chemical reactions take place. These chemical reactions cause chemical effects in the conducting solution.
(c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the negative terminal of the battery.
Explanation: When we pass current through copper sulphate solution, then at the negative electrode, the positive ions (Cu2+) gain electrons at the negative electrode, and are reduced to pure Copper, which is thus deposited there.
(d) The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.
Explanation: Electroplating a process that used electric current to deposit dissolved ions to form layers of pure metal on the electrode.
Question 2.
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
Answer:
The electric current is capable of producing magnetic effect which causes deflection of the magnetic needle of a compass. So, when the free ends of a tester are dipped into a solution, current is able to pass through the solution because it is a good conductor of electricity. Therefore, the needle shows deflection.
Question 3.
Name three liquids, which when tested in the manner shown in Fig. 14.9, may cause the magnetic needle to deflect.
Answer:
The Liquids that conduct electricity will cause the magnetic needle to deflect because the electric current is capable of producing magnetic effect the liquids like lemon juice, salt water and vegetable oil allow electricity to pass through them. Hence, these liquids can be used as in the beaker to show the given effect.
Question 4.
The bulb does not glow in the setup shown in Fig. 14.10. List the possible reasons. Explain your answer.
Answer:
There could be several possible reasons for not glowing of the bulb:
1) The bulb may be fused before connecting to the circuit.
2) Even after replacing the bulb if it does not glow, then the connection may have some loose point.
3) Even after repairing the connections, if the bulb does not glow that means the solution is not conducting solution.
Question 5.
A tester is used to check the conduction of electricity through two liquids, labelled A and B. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. You would conclude that
(i) liquid A is a better conductor than liquid B.
(ii) liquid B is a better conductor than liquid A.
(iii) both liquids are equally conducting.
(iv) conducting properties of liquid cannot be compared in this manner.
Answer:
The correct option is answer(i). Because current flows more easily throughout liquid A than B. Thus A is a better conductor than liquid B.
Question 6.
Does pure water conduct electricity? If not, what can we do to make it conducting?
Answer:
No. Pure water does not conduct electricity. Pure water does not contain any ions which make it conducting. But it can conduct electricity when a pinch of common salt is added to it, as salt solution is conducting in nature.
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:
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.
Question 8.
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:
Sea water contains more dissolved salts than the drinking water because drinking water is made pure by many methods. Therefore, seawater is more conducting than normal drinking water. Because of this reason, the compass needle deflects more in seawater than in the drinking water.
Question 9.
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.
Question 10.
Paheli had heard that rain water is as good as distilled water. So, she collected some rain water 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:
Rain water contains dissolved salts. This makes it a conducting solution. There are no dissolved salts present in the distilled water because it is made pure by certain methods. Hence, rain water can allow electricity to pass through it while distilled water cannot.
Question 11.
Prepare a list of objects around you that are electroplated.
Answer:
The objects are electroplated so as to avoid objects from being corroded. Few of them are shown below:
1) Artificial jewellery items are gold or silver plated. Because gold and silver does not corrode with air.
2) Iron used in constructing a building is coated with a layer of zinc to protect it from rusting.
Question 12.
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 the battery and why?
Answer:
Copper ion is positively charged. It will be attracted towards the plate which is connected to the negative terminal of the battery. Because positive charges attract negative charges and repel positive charges. As copper ions are transferred to the thin copper plate, this thin pure copper plate must be connected to the negative terminal of the battery. Consequently, impure copper rod is connected to the positive terminal of the battery.
