Class 9 Science Note

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Ionisation

Ions are the charged particle of an atom which carries positive or negative charge. Ions are produced when ionic substances are kept in a solution which undergoes dissociation into two components, one in positively charged component and the other in negatively charged component. For example: ionization of NaCl.

The process of decomposition of chemical compound into ions is known as ionization.

 Example: NaCl              Ø                 Na+ + Cl-

 

 

Electrolysis

The process of the decomposition of the electrolytic solution into constituent when the electric current is passed through it is called Electrolysis.

 The process of the separation of the metal from its ores is done through electrolysis. Molecules of an electrolyte which can easily break down into the ions are strong electrolyte.

 

 

Electrolysis of water

The process of the decomposition of the water into oxygen and hydrogen gas when the electric current is passed through the water is called Electrolysis of water.

 

When dil. H2SO4 is mixed with water

H2O (HOH)  →   H++ OH-

 

At anode

OH-- → OH + e-

4OH → 2H2O + O2

 

At cathode

H+   + e- → H

4H → 2H2                      

 

Overall reaction is

2H2O →   2H2 + O2

 

Electrolysis of copper sulphate

 

 

 

During the electrolysis of copper Sulphate, the copper Sulphate breaks down into Cu++ and SO4--solution. When the solution is electrolyzed, Cu++ ions move towards cathode and SO4—ions move towards anode. At the cathode, Cu++ ion receives two electrons and become neutral Cu atom, and at anode, SO4—ion releases two electrons to form SO4 radical. This results the separation of Cu++ ions from anode which move in the electrolyte.

 

 

 

Electroplating of copper

 

 

Here CUSO4 solution is taken as electrolyte. When the electric current passes through the circuit, thin layer of the copper is deposited over the metal.

 

Chemical reaction involved

‘When CuSO4 dissolves in water

CuSO4→  Cu++ + SO4

 

At anode:      Cu   +   SO4 →      CuSO4 + 2e

At cathode:    Cu++ +2e       →   Cu

 

 

Uses of electrolysis

Purification of metal

Electroplating

Extraction of metal

Production of hydrogen and oxygen gas


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