Quick Revision Notes & Formula Sheet

Class: 8th Science
Board: MP Board (Madhya Pradesh)
Chapter: Chemical Effects of Electric Current

### 1. Important Definitions (महत्वपूर्ण परिभाषाएँ)

Electric Current (विद्युत धारा): The flow of electric charges through a conductor.
Good Conductors (सुचालक): Materials that allow electric current to pass through them easily (e.g., metals like copper, iron, and tap water).
Poor Conductors / Insulators (कुचालक): Materials that do not allow electric current to pass through them easily (e.g., rubber, plastic, wood, and distilled water).
Electroplating (विद्युत लेपन): The process of depositing a layer of any desired metal on another material by means of electricity.
LED (Light Emitting Diode): A glowing device used in testers to detect even a weak electric current. It glows even when a very small current passes through it.
Electrolyte (विद्युत अपघट्य): A liquid that conducts electricity and undergoes chemical changes (decomposition) when electric current passes through it.
Electrodes (इलेक्ट्रोड): Metal rods or plates immersed in an electrolyte through which electric current enters and leaves the solution.
- Cathode (कैथोड): The electrode connected to the negative terminal of a battery.
- Anode (एनोड): The electrode connected to the positive terminal of a battery.

Most liquids that conduct electricity are solutions of acids, bases, and salts.
Distilled Water (शुद्ध जल) is a poor conductor of electricity because it is free of salts.
Adding a little common salt (NaCl), acid, or base to distilled water makes it a good conductor.

When electric current passes through a conducting solution, some chemical effects take place:

Gas Bubbles: Bubbles of gas may be formed at the electrodes (e.g., Hydrogen at the cathode, Oxygen at the anode during the electrolysis of water).
Deposit of Metal: Deposits of metal may be seen on electrodes (metal coating).
Change of Color: Color changes of solutions may occur depending on the current and solutions used.

Electroplating is a prime application of the chemical effects of electric current.

Setup Requirements:
- An electrolyte (a salt solution of the metal to be deposited).
- An anode (made of the coating metal).
- A cathode (the object to be coated).
- A DC source (Battery / Cell).
Working Principle:
- When the electric current passes through the electrolyte solution, the metal salt breaks down.
- The free metal ions are drawn towards the cathode (object) and get deposited on its surface, forming a shiny, protective, or decorative layer.
Common Applications of Electroplating:
- Chromium Plating: Done on car parts, bath taps, wheel rims, etc., to give a shiny appearance and prevent rust.
- Gold and Silver Plating: Used for plating cheaper metals to make artificial jewelry look like gold or silver.
- Tin Plating: Used on iron cans used for storing food, because tin is less reactive than iron and prevents food from spoiling.
- Zinc Plating: Done on iron objects (like bridges and-road barriers) to protect them from corrosion and formation of rust.

Why use an LED instead of a bulb? An ordinary bulb requires a higher current to heat its filament enough to glow. An LED glows even with a very weak current.
Why is tap water a conductor? Because it naturally contains small amounts of dissolved mineral salts.
Waste disposal: Electroplating factories discharge polluting chemical waste. Safe disposal methods must be followed to protect the environment and water bodies.