BAL BHARATI PUBLIC SCHOOL, PITAMPURA, DELHI-110034
CLASS-8 Term I (2013-2014)
CHEMISTRY NOTES
CHEMICAL EFFECTS OF CURRENT
Q1. What are good and bad conductors of electric current?
Ans. Good conductors of current: Those materials which allow electric current to pass
through them are called good conductors of current.
Example: Copper, iron etc.
Bad conductors of current: Those materials which do not allow electric current to pass
through them are called bad conductors of current.
Example: Plastics, wood etc.
Q2. What is the purpose of a tester?
Ans. The purpose of a tester is to check whether a material allows electric current to pass
through it or not.
Q3. Why do we use a battery instead of a cell while testing the conductivity of current through a
liquid?
Ans. We use a battery as the current generated by the liquids is very weak which cannot be
detected by using a cell.
Q4. A tester was made to test the conductivity of salt solution. However the bulb of the tester did
not glow. What could be the possible reasons?
Ans.
a) The connections are loose.
b) The filament of the bulb is broken.
c) The battery is discharged.
Q5. Identify the following solutions as good or bad conductors of electricity:
a) Vinegar
Good conductor
b) Soap solution
Good conductor
c) Mustard oil
Bad conductor
d) Honey
Bad conductor
e) Petrol
Bad conductor
f) Sugar solution
Bad conductor
g) Copper Sulphate solution
Good conductor
Q6. Why should not we join the two free ends of a tester when it is not in use?
Ans. We should not join the two free ends of a tester when it is not in use so as to avoid the
wastage of battery.
Q7. Suggest the possible alternatives to test the conductivity of a weakly conducting solution.
Ans. To test the conductivity of a weakly conducting solution:
a) We can replace the bulb of a tester with an LED.
b) We can use a magnetic compass.
Q8. Why does not pure water conduct electricity? How can we make it conducting?
Ans.Pure water does not conduct electricity because of the absence of charged particles called
ions in it.
It can be made conducting by adding a salt, an acid or a base in it.
Q9.
a)
b)
Ans.
a)
b)
What is the full form of LED?
Why is it preferred over a bulb while making a tester?
Light emitting diode.
An LED is preferred as it can glow even when the current passing through a circuit is
weak.
Q10. Why should we not touch the electrical equipment with wet hands?
Ans. We should not touch the electrical equipment with wet hands as tap water and human
body are good conductors of electricity, so we can get an electric shock.
Chemical Effects of electric current – Part II (half yearly portion)
Q1. What changes are seen when an electric current is passed through a conducting solution ?
Ans. i. Bubbles of gas may be formed.
ii. Deposits of metals may be seen over electrodes.
iii. Change in colour of solution my occur.
Q2. What products are formed during the electrolysis of water?
Ans. Decomposition of water by the passage of electric current is known as electrolysis of
water.
Electrolysis of water leads to formation of Hydrogen gas at the cathode and Oxygen at the
anode.
Q3. What is electroplating?
Ans: Deposition of a layer of metal over another by means of electricity is called electroplating.
Q4. What is an electrolyte ? Give some examples.
Ans: Any solution that conducts electricity is known as an electrolyte. Acids, Bases and
Salt solutions are some electrolytes.
Q5. Explain how electroplating of one metal can be done over another metal by taking a
suitable example.
Ans: In electroplating of Gold over Copper, Copper is made as cathode by connecting to
the negative terminal of the battery. Gold which has to be deposited over the Copper is made as
anode by connecting to the positive terminal of the battery.
Electrolyte is the salt solution of Gold. When the circuit is complete, Gold from the
anode will go into the solution and an equivalent amount of Gold from the solution
will be deposited over Copper (Cathode) thus causing its electroplating over
Copper.
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