chemical effects of electric current

1. Assignment for Class 8 Chemistry on Chemical Effects of Electric Current
Name_________________________________ School____________________________ Date_________________
SUPRATIM DAS│DURGAPUR-WEST BENGAL # 9434008713
Question 1: sdas.durgapur@gmail.com
Which of the following cannot be charged easily by friction?
(a) A plastic scale (b) A copper rod
(c) An inflated balloon (d) A woollen cloth
Question 2:
When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
Question 3:
Write T against true and F against false in the following statements.
(a) Like charges attract each other.
(b) A charged glass rod attracts a charged plastic straw.
(c) Lightning conductor cannot protect a building from lightning.
(d) Earthquakes can be predicted in advance.
Question 4:
Define-Electrolysis, Electrometallurgy, Electroplating and Electrodes.
Question 5:
Explain why a charged body loses its charge if we touch it with our hand.
Question 6:
Name two weak electrolytes.
Question 7:
Define: Conductor, Non-conductor and Insulator
Question 8:
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is
attracted by another charged balloon?
Question 9:
Describe with the help of a diagram an instrument which can be used to detect a charged body.
Question 10:
List two types of electrolytes depending on their degree of ionization.
Question 11:
What is LED?
Question 12:
What is the difference in conductivity of pure water and lemon juice?
Question 12:
Fill in the blanks by correct words:
(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 ___________________.
Question 13:
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you
Question 14:
Name three liquids, which when tested in the manner by passing electricity, may cause the magnetic needle
to deflect.

2. Question 15:
The bulb does not glow in the setup having a liquid connected with battery. List the possible reasons.
Explain your answer.
Question 16:
Does pure water conduct electricity? If not, what can we do to make it conducting?
Question 17:
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.
Question 18:
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?
Question 19:
Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Explain.
Question 20:
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?
Question 21:
Prepare a list of objects around you that are electroplated.
Question 22:
The purification of copper is described as-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?
Question 23:
Predict the following as conducting or non-conducting:
a) Pure water b) NaCl solution
c) Milk d) Cooking oil
Question 24:
Write all the materials required to show water containing any salt or acid or alkali is a good conductor of
electricity.
MATRIX MATCHTYPE:
Match the following facts/processes with their correct name:
Process details Name of the products/others
a) Molten sodium chloride i) Insulators
b) Electrolysis of water ii) weak electrolytes
c) PVC and wood iii) 2:1 ratio of hydrogen : oxygen
d) Solution of CH3COOH in H2O iv) degree of ionization is very high
e) KCl + water v) preventing corrosion
f) Electroplating vi) strong electrolytes

3. Assignment for Class 8 Chemistry on Chemical Effects of Electric Current
Answer and solution
Question 1: Answer:
(b) A copperrod
Only non-conducting materials can be easily charged by friction. Copper is a highly conducting materials. Therefore, a copper rod
cannot be charged easily by friction.
Question 2: Answer:
(b) The rod becomes positively charged, while the cloth has a negative charge.
When an object is charged by rubbing it against another object, the two objects get oppositely charged.By convention,it is
considered that the charged acquired by the glass rod is positive and charged acquired by the cloth is negative. Therefore, the rod
becomes positively charged and the cloth becomes negatively charged.
Question 3: Answer:
(a) False
Like charges repel each other. It is the unlike charges that attract each other.
(b) True
A charged glass rod has positive charges on its surface while a charged plastic straw has negative charges on its surface. Since
unlike charges attract each other, a charged glass rod attracts a charged plastic straw.
(c) False
During a lightning, the lightning conductorconducts all the atmospheric charges to the Earth directly, leaving the building safe.
Hence, lightning conductors protect a building from lightning.
(d) False
Although the causes of earthquakes is known, but no instrument could be invented to detect it till now. Hence, earthquakes cannot
be predicted in advance.
Question 5: Answer: When we touch a charged object, our body conducts its charges to the earth. That is why a charged body
loses its charge, if we touch it with our hand. This phenomenon is known as electric discharge.(Prachi-216)
Question 8:Answer: The nature of charges present on the surface of charged balloons are similar. Since like charges repel each
other, two charged balloons repel each other. When a charged body is brought near an uncharged body,the uncharged body
acquires charges on its surface caused by the induction of charges. The charges are of opposite nature in relation to the cha rged
body.Since unlike charges attract each other, a charged body always attracts an uncharged body.Hence, an uncharged balloon is
attracted by anothercharged balloon.
Question 9: Answer: An electroscope can be used to detect whether a body is charged or not. The following figure shows a
simple electroscope. It consists ofa metal rod. At one end of the rod, two leaves of aluminium foil are fixed and at the other end,
there is a metal disc. The leaves of aluminium foil are placed inside a conical flask and the flask is corked to isolate the leaves
from air.
When the metal disc is touched with a charged body, the aluminium strips move away from each other. This happens because
some of the charges of the body are transferred to the strips through the metal rod. This method of charging a body is called
charging by conduction.The nature of charges on both the leaves and the charged body are the similar. Hence, both the leaves of
the aluminium foil will move away from each other. If the body was not charged,then the leaves of the foil would remain as t hey
were before. They would not repel each other.
Question 12: Answer:
(a) Most liquids that conduct electricity are solutions of __acids__,__bases__ and __salts__.
(The solutions ofacids, bases orsalts are conducting in nature. They allow the current to pass through.)
(b) The passage ofan electric current through a solution causes __chemical__ effects.
(When an electric current passes through a solution,the solution decomposes into its positive and negative ions. This process of
decomposition of the solution is a chemical effect.)
(c) If you pass current through copper sulphate solution,copper gets deposited on the plate connected to the __negative__ terminal
of the battery.
(When an electric current passes through a coppersulphate solution, the solution decomposes into positively charged copper ions
and negatively charged sulphate ions. These positively charged copper ions get attracted towards the plate which is connected to
the negative terminal of a battery.)
(d) The process of depositing a layer of any desired metal on another material by means of electricity is called __electroplating__.

4. Question 13:
Answer:
The deflection in the compass needle shows that current is flowing through the wounded wire and hence, through the circuit. The
circuit is complete since free ends of the testerare dipped in a solution. The solution is certainly a conducting solution.
This is the reason why the compass needle shows a deflection.(prachi-224)
Question 14:
Name three liquids, which when tested in the manner by passing electricity, may cause the magnetic needle to deflect.
Answer:
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.
Answer:
The bulb may not glow because of the following reasons:
(i) Liquid in the beaker is non-conducting.In such case, the electric current would not be able to pass through the liquid. Hence,
the circuit is not complete.
(ii) Electric current in the circuit is very weak. This can happen if the material used for making the circuit is not a good conductor
of electricity or the battery does not have sufficient energy to generate electricity.
Question 16:
Answer:
No. Pure water does not conduct electricity. This is because pure water is devoid of any salts. Pure water can conduct electricity
when a pinch of common salt is added to it, as salt solution is conducting in nature.
Question 17: Answer: 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. That is why, in case of a fire, the firemen shut
off the main electrical supply for the area before they use the water hoses.
Question 18: Answer: Sea water contains more dissolved salts than the drinking water. Hence, it is more conducting than the
drinking water. Because of this reason,the compass needle deflects more in seawater than in the drinking water.
Question 19: Answer: No. It is not safe to repair electrical appliances outdoors during heavy downpour.
This is because rain water contains dissolved salts.Therefore, rain water can conduct electricity. The electrician may get electrical
shocks while working outdoors during rain.
Question 20: Answer: Rain water contains dissolved salts.This makes it a conducting solution.There are no dissolved salts
present in the distilled water. Hence, rain water can allow electricity to pass through it while distilled water cannot.
Question 21: Answer: Examples of electroplated objects are as follows:
(i) Chromium plating is done on different parts of cars, buses and motor cycles to give them shiny appearance.
ii. A fine layer of gold is deposited on the silver ornaments and they are called gold-plated ornaments.
ii. Iron used in constructing a building is coated with a layer of zinc. This protects iron from corrosion and rusting.
Question 22: Answer: Copper ion is positively charged. It is attracted towards the plate which is connected to the negative
terminal of the battery. As copperions are transferred to the thin copper plate, this thin pure copper plate must be connect ed to the
negative terminal of the battery. Consequently,impure copper rod is connected to the positive terminal
of the battery.
Match the following facts/processes with their correct name:
Process details Name of the products/others
a) Molten sodium chloride (iv-vi) i) Insulators
b) Electrolysis of water (iii) ii) weak electrolytes
c) PVC and wood (i) iii) 2:1 ratio of hydrogen : oxygen
d) Solution of CH3COOH in H2O (ii) iv) degree of ionization is very high
e) KCl + water (iv-vi) v) preventing corrosion
f) Electroplating (v) vi) strong electrolytes