Class 9 - Chemistry - Chapter 8

Electro-Chemistry

Electro-Chemistry:

The branch of chemistry which deals with the study of chemical energy to electrical energy or electrical energy to chemical energy is called electro-chemistry.

Conductors:

Those substances through which electric current can pass are called conductors. For example all metals are conductors.

Non-Conductors:

Those substances through which electric current cannot pass are called non-conductors. For example plastic, wood are non-conductors.

Electrolysis:

The process in which electricity passes through the aqueous or infused state of some substance. The substances itself decompose into its component. This process is called electrolysis.

Electrolyte:

The compound in molten state or in aqueous solution through which electricity can pass are called electrolyte.

Non-Electrolyte:

Those compounds through which electricity cannot pass are called non-electrolyte.

Strong Electrolyte:

The substances which are highly soluble and completely ionized are called strong electrolyte. For example acids, bases and salts are strong electrolytes.

Weak Electrolyte:

The substances which are not highly soluble and remain in un-ionized form are called weak electrolyte.

Electroplating:

A process in which metal is deposited on the surface of another metal by electrolysis is called electroplating.

Objectives of Electroplating

Decoration

It is done for decoration. Noble and precious metals like gold or silver are deposited on the inferior metals to enhance their beauty and look beautiful.

Protection

Electroplating is done to protect the metals from rusting as well as from attack of other substance like organic acids and acidic gases.

Repair

It can be used to repair the broken machinery by electroplating with other metals. Usually the metals like copper, silver, chromium, nickel and gold are used for electroplating.

Procedure of Electroplating

The metal which is to be electroplated is first cleaned with sand and then washed with caustic soda solution and finally with a lot of water.

This metal is made cathode and the metal which is going to be deposited is made anode. The electrolyte is a salt of metal being deposited and electroplating is carried out in a tank made of cement, glass or wood. It is called an electrolytic tank.

The electrolyte should have following properties:

1. It must be very soluble in water.

2. It must be good conductor.

3. Cheap

4. May not easily oxidized or reduced or hydrolyzed.