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Electric Current and Its Chemical Effects

CBSE Class 8 Science • Chapter 16 • Detailed Master Notes

Chapter Overview

We know that solid metals like copper and aluminium conduct electricity. In this chapter, we explore whether liquids can conduct electricity and the chemical changes that occur when current flows through a conducting solution.

16.1 Do Liquids Conduct Electricity?

Some liquids are good conductors of electricity, and some are poor conductors. To test whether a liquid allows electric current to pass through it, we can use a tester consisting of a cell, a bulb or LED, and conducting wires.

Good Conductors: Materials which allow electric current to pass through them are good conductors of electricity. Examples: Lemon juice, vinegar, tap water.

Poor Conductors: Materials which do not allow electric current to pass through them easily. Examples: Distilled water, honey, vegetable oil.

Why does Tap Water Conduct Electricity?

The water that we get from sources such as taps, hand pumps, and wells is not pure. It contains small amounts of mineral salts dissolved in it. These dissolved salts make it a good conductor of electricity.

By contrast, distilled water is free of salts and is a poor conductor of electricity.

Topic Practice: Conductors

Q1. Why should you never handle electrical appliances with wet hands?

Ans: Ordinary water (like tap water) contains dissolved salts, making it a good conductor of electricity. Touching electrical appliances with wet hands risks letting current flow into the body, causing a dangerous electric shock.

16.2 Chemical Effects of Electric Current

When electric current passes through a conducting solution, it causes chemical reactions. This is called the chemical effect of electric current.

A British chemist, William Nicholson (1753–1815), showed that if electrodes were immersed in water and a current was passed, bubbles of oxygen and hydrogen were produced.

Signs of Chemical Effects

The passage of an electric current through a conducting liquid causes chemical reactions. The resulting effects are:

Formation of gas bubbles: Bubbles of gas may be formed on the electrodes.
Metal deposits: Deposits of metal may be seen on electrodes.
Change in colour: Changes of colour of solutions may occur.

16.3 Electroplating

One of the most common applications of the chemical effects of electric current is electroplating.

Electroplating: The process of depositing a layer of any desired metal on another material by means of electricity is called electroplating.

How Electroplating Works (Example: Copper Plating)

Take copper sulphate solution in a beaker. This acts as the conducting liquid (electrolyte).
Take a copper plate and connect it to the positive terminal of the battery.
Take the object to be coated (e.g., an iron spoon) and connect it to the negative terminal of the battery.
When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate.
The free copper gets drawn to the electrode connected to the negative terminal (the spoon) and gets deposited on it.
To keep the solution balanced, an equal amount of copper dissolves from the copper plate (positive terminal) into the solution.

AI Image Prompt: A scientific diagram showing electroplating. A glass beaker containing blue copper sulphate solution. Inside the beaker, a solid copper plate is on the left (positive terminal), and a metal spoon is on the right (negative terminal). Wires connect them to a battery at the top. Clean lines, educational style.

Uses of Electroplating

Automobile parts and bathroom taps: Chromium plating is done on these objects. Chromium has a shiny appearance, does not corrode, and resists scratches. However, chromium is expensive, so objects are made from a cheaper metal and only coated with chromium.
Jewellery: Makers electroplate silver and gold on less expensive metals to make artificial jewellery appear expensive but cost less.
Tin Cans: Tin cans used for storing food are made by electroplating tin onto iron. Tin is less reactive than iron, preventing the food from spoiling.
Iron Bridges: Iron is used in bridges and automobiles to provide strength. A coating of zinc is deposited on iron to protect it from corrosion and rust.