CBSE Notes Class 8 Science Chapter 11 - Chemical Effects of Electric Current

Electric current not only powers our devices but also causes chemical changes in substances, a phenomenon called the chemical effects of electric current. When a current flows through a conducting solution, it can trigger reactions that create new substances. Metals such as copper and aluminum are classified as good conductors, while materials like rubber and glass are considered poor conductors. 

1.0Conductors And Insulator

• The materials which conduct electricity are called good conductors of electricity. Example-Iron, Copper, Human Body
• The materials which don’t conduct electricity at all are bad conductors of electricity. Example- Plastic, Glass, Rubber
• There are also some material which conduct electricity under specific conditions. They are not completely bad conductors. Example-Tungsten Filament in a Bulb

2.0Good And Poor Conductor of Electricity

• For any solution to conduct electricity, we need ions or free electrons.
• Pure water does not conduct electricity, but naturally occurring water(rain water, tap water etc.) contains salts(ions) dissolved in it and this makes it a good conductor of electricity.
• Soda compounds (a common name for chemicals mostly containing sodium) contain ions when dissolved in water and ions help conduct electricity.

3.0Chemical Effects of Electric Current

when electricity flows through a conducting solution

Experiment

1. Take two carbon rods from two discarded cells, These two  rods are called electrodes.
2. Clean their metal caps. Wipe them dry.
3. Tie copper wires around the metal caps of the carbon rods. Join the ends of the copper wires to a battery.
4. Take a solution which is a good conductor of electricity (tap water, lemon juice) . Immerse the rods in the solution such that the metal caps are outside the water.
5. Now the circuit is complete. Wait for about 5 minutes.

Observation: Bubbles are observed near the electrodes when current passes through them.

Analysis

• The above changes are seen due to the Chemical Effects of Electric Current. The transition of electric current through a conduction solution causes one or any of the following reactions depending on the solution and electrode used
• Bubbles of gas are seen on the electrodes.
• Metal deposits can be seen on the electrodes.
• The solution could change colors.

4.0Electroplating

The process of applying a layer of a specific metal onto another material using electricity is known as electroplating.

Artificial jewellery is shining when it is new and after sometime it begins to lose its shine. Same case with bicycle handlebars, nuts, bolts etc. This is because these metals are coated with another metal to give it their lustrous appearance and still keep it cost effective.

Experiment:

1. Take distilled water in a beaker and dissolve some copper sulphate in it. Add a couple of  drops of dilute sulphuric acid to it to make it more conducting.
2. Take two clean copper plates, Clean it with sandpaper, then wash them with water and dry them.
3. Combine the copper plates to the terminals of the battery.
4. Immerse them in the copper sulphate solution.
5. Allow the current to pass through the circuit for 15 minutes.
6. Remove the electrodes and observe them.

Observation:

• The plate connected to the positive terminal looks corroded.
• The plate connected to the negative terminal has a thin layer of metal on its surface.

Analysis:

• The above changes are seen due to the Chemical Effects of Electric Current.
• When electric current passes through the copper sulphate solution, the copper sulphate dissociates into copper and sulphate.
• The free copper gets attracted towards the negative terminal and is deposited on the plate connected to the negative terminal.
• The copper present in the copper plate which is connected to the positive terminal gets dissolved in the copper sulphate solution, thus replacing the loss of copper from the solution.
• And this process continues, This process is called Electroplating.

Applications of Electroplating

• Artificial jewellery usually made of less expensive metals is often plated with a thin layer of precious metal like gold and silver to make it more lustrous and appealing but cheaper.
• Many industrial applications use electroplating to create a protective barrier on a metal substrate. This protective barrier prevents tarnishing and gives a glossy appearance.