Lesson: Chemical Effects of
Electric Current
Topic 1: Liquids Conducting Electricity
Give examples of two poor conductors of electricity.
Plastic and Bakelite are two poor conductors of electricity.
Is distilled water a good conductor?
No, distilled water is a poor conductor of electricity. Since distilled water lacks any dissolved salts, it cannot conduct electricity.
Ordinary water can conduct electricity while distilled water does not. Justify.
Ordinary water contains several salts dissolved in it, so it conducts electricity, whereas distilled water is devoid of salts and thus is a poor conductor of electricity.
Name two liquids which are good conductors of electricity.
Lemon juice and sulphuric acid are examples of good conductors of electricity.
A set up of a liquid, battery and bulb are connected, but the bulb doesn’t glow. List down possible reasons for this.
The reasons could be one of the following:
• Loose circuit connections
• Fused bulb
• Battery discharged
• The liquid is a poor conductor
Sometimes a tester bulb doesn’t glow even when the liquid is a good conductor. Why? What alternative arrangement can be made to correct this?
Sometimes the bulb doesn’t glow because the amount of electric current is not enough to heat the element in the bulb. We can replace the bulb with an LED which is much more sensitive to a low current.
How can distilled water be turned into a conducting liquid?
We can convert distilled water into a conducting liquid by introducing impurities such as common salt.
What is the full form of LED?
Light Emitting Diode
What is electrolysis?
Electrolysis is a process in which a liquid (electrolyte) goes through chemical change due to the passage of electricity through it.
How does a bulb connected to a tester glow when the tester is connected through an electrolyte?
When the two ends of a tester are connected through an electrolyte, it allows the electric current to pass, thus completing the circuit of the tester and causing the bulb to glow.
What happens when electricity is passed through a liquid that conducts electricity?
When electricity is passed through a liquid, one or more of the following observations are possible:
a) Bubbles may get formed at one or both ends of the wire dipped in the liquid
b) Colour of the liquid may change
c) A deposit may be formed on one of the two ends of wire dipped in the liquid.
Before a fireman can use a hose pipe to put off a fire in a building, the mains switch is turned off. Why?
Ordinary water has small amount of impurities dissolved in it and thus is a conductor of electricity. If the fireman uses his hose pipe with the electricity turned on, water will start conducting electricity, giving a severe shock to all that come in contact with it. Hence, the mains is turned off before the fireman uses a water hose.
Why do acids, bases and salt solutions conduct electricity?
Electrical conductivity is the property of a substance to allow free passage of current. In the case of an acid, base or salt, a chemical reaction occurs due to passage of current since they have ions and hence, they conduct electricity.
You are using a magnetic compass to test the conductivity of two liquids: concentrated hydrochloric acid and dilute hydrochloric acid. What difference will you notice and how did you arrive at this conclusion?
The magnetic compass will show a deflection only for conducting liquids and will be greater with the increase in ions. In case of dilute hydrochloric acid, the deflection will be less than that in concentrated hydrochloric acid, as the concentration of salt is lower.
Topic 2: Application of Electrolysis
Define electroplating.
The process of creating a deposit of one metal or another using electric current to induce a chemical reaction is called electroplating.
List the advantages of electroplating.
Advantages of electroplating are as follows:
• Protects metals from corrosion
• Prevents metal surfaces from rusting
• Dull metals can be coated with shiny metals to make them look good
• Jewels made from cheap metals are made rich by electroplating with gold/silver.
If you have to coat iron with silver, what would be your cathode and anode?
In order to coat iron with silver, iron is used as a cathode and silver as anode.
If you have to coat copper with nickel, what would be your cathode and anode?
In order to coat copper with nickel, copper is used as a cathode and nickel as anode.
How do you choose the electrodes while electroplating?
There are three main components interacting in an electroplating process, cathode, anode and an electrolyte. The cathode is the piece to be plated, anode is the plating metal and the electrolyte is a salt solution of the anode.