notes prepared by subhankar Karmakar
Chemical effects of electric current
The materials which allow electric current to pass through them easily are called good conductors of electricity.
The materials which do not allow electric current to pass through them easily are called poor conductors of electricity or non conductors of electricity.
The liquids that conduct electricity solutions of acids bases and salts in water. There are some important differences in the conduction of electricity by solids such as metals and liquids such as solutions of acids bases and salts.
1. In solids like metals, electricity is carried by electrons but in liquids electricity is carried by ions positively charged ions and negatively charged ions.
For example, in a solid like copper metal, electricity is carried by electrons but in a liquid like copper sulphate solution, electricity is carried by copper ions and sulphate ions.
2. When electricity is passed through a solid then no chemical change takes place but when electricity or electric current is passed through a liquid then a chemical change takes place.
For example, when electricity is passed through a copper wire, no chemical change takes place in it, but when electricity is passed through acidified water, then a chemical change takes place in which water is decomposed into hydrogen and oxygen gases.
The liquids which conduct electricity are called conducting liquids.
The chemical changes which takes place in conducting liquids on passing electric current through them are called chemical effects of electric current.
ELECTROLYTES:
A liquid or solution of substance which can conduct electricity is called an electrolyte. The solutions of acids, bases and salts in water are called electrolytes.
Electrolytes are of two types: strong electrolytes and weak electrolytes.
Strong electrolyte is a liquid or solution which conducts electricity very well. Strong electrolyte is a very good conductor of electricity because it contains a lot of ions in it. Some examples of strong electrolytes are sulphuric acid solution, hydrochloric acid solution, nitric acid solution, sodium hydroxide solution, potassium hydroxide solution, common salt solution etc.
Weak electrolyte is a liquid or solution which conducts electricity to a lesser extent. A weak electrolyte is a weak conductor of electricity because it contains less number of ions. Examples of weak electrolytes are: vinegar, lemon juice, carbonic acid solution, ordinary water and rainwater.
ELECTRODES:
"A solid electrical conductor through which an electric current enters or leaves something like to a dry cell or an electrolytic cell is called an electrode."
Electrodes are of two types: Anode and Cathode.
The positively charged electrode is called anode and the negatively charged electrode is called cathode.
Metal rods and carbon rods can be used as electrodes.
ELECTROLYTIC CELL:
"An arrangement having two electrodes kept in a conducting liquid or electrolyte in a vessel is called an electrolytic cell."
For example, if we keep two carbon electrodes in a beaker containing acidified water it will be an electrolytic cell.
An experiment to test whether a liquid conducts electricity or not:
We take a small beaker and fixed two iron nails on a rubber cork about 1 cm apart and place this cork in the beaker. We connect the two nails to the two terminals of a battery by including a torch bulb and a switch in the circuit. Now we shall consider three cases.
(1) Good conductors of electricity:
Now we pour a solution of dilute hydrochloric acid in the beaker carefully. Now we pass electric current through the hydrochloric acid solution by closing the switch. As soon as we switch on the current, the bulb starts glowing brightly. The glowing bulb in this case tells us that hydrochloric acid solution conduct electricity and it is a good conductor of electricity.
(2) Non conductors of electricity:
If we take sugar solution instead of hydrochloric acid solution, the bulb does not glow. It says that, sugar solution does not conduct electricity. It is not an electrolyte.
(3) Weak conductors of electricity:
if we take lemon juice or vinegar instead of hydrochloric acid solution, the bulb glows dimly. It indicates that vinegar and lemon juice conduct electricity but they are weak conductors of electricity.
Detection of weak current flowing through a liquid:
The weak electric current flowing through liquids can be detected in two ways.
1. By using a LED in the circuit.
LED is a semiconductor device which glows even when a very weak current passes through it. There are two wires or leads attached to an LED. The longer lead should be connected to the positive side of the battery.
We take a small beaker and fixed two iron nails on a rubber cork about 1 cm apart and place this cork in the beaker. We connect the two nails to the two terminals of a battery by including a LED and a switch in the circuit.
If we pour vinegar or lemon juice in the beaker and closes the switch, LED will glow. It proves that the vinegar or lemon juice solution can conduct weak electricity through it.
2. By using a compass surrounded by turns of circuit wire.
We take out the cardboard tray from the inside of the discarded Matchbox. Place small compass inside this cardboard tray. Wrap and electric wire a few times around the cardboard tray so as to make a type of coil of wire around the compass. The Matchbox tray containing the compass inside it and having wound up around it is connected in place of torch bulb in the circuit of the liquid to be tested for conductivity. Even if a weak electric current flows through the liquid in the circuit the magnetic needle of compass will show deflection. If a compass surrounded by wound up electric wire of a circuit including a liquid in it shows deflection, it will mean that the liquid conducts electricity.
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