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Class 8, Science, Chapter-11, Lecture-2, Electrolysis (Notes)

ELECTROLYSIS: 

The chemical decomposition produced by passing an electric current through an electrolyte solution is called electrolysis.

ELECTROLYSIS of Water: 

The chemical decomposition of water into Hydrogen and Oxygen produced by passing an electric current through acidified or alkaline water is called electrolysis of water.

$${{\rm{WATER}}\mathrel{\mathop{\kern0pt\longrightarrow}
\limits_{Chemical{\rm{ }}{\mathop{\rm Re}\nolimits} action}^{Electric{\rm{ }}Current}} \mathop {{\rm{HYDROGEN}}}\limits_{{\rm{(Cathode)}}}  + \mathop {{\rm{OXYGEN}}}\limits_{{\rm{(Anode)}}} }$$

In the process: 

  1. One Graphite rod acts as Anode ( +ve ) 
    Another Graphite rod acts as Cathode ( –ve )
    Acidified water acts as electrolyte.
  2. Oxygen Gas is formed at Anode
  3. Hydrogen Gas is formed at Cathode

ELECTROPLATING: 

The process of depositing a thin layer of a desired metal over a metallic object with the help of electric current is called electroplating. 

In the process: 

  1. Metal to be deposited acts as anode ( +ve )
    Metallic Object acts as cathode ( –ve )
    Solution of the Salt of the metal to be deposited act as electrolyte.
  2. Metal at anode becomes positive ions an goes to the electrolyte
  3. Positive metal ions from electrolyte goes to the Cathode.
  4. Ions of Desired metal becomes atoms and gets deposited over the metallic object at cathode

ELECTROLYTIC REFINING: 

The purification of impure metal by electrolysis of metal salt in which impure metal acts as anode and pure metal acts as cathode is called electrolytic refining. 

  • used for copper, gold, zinc, chromium, nickel

In the process: 

  1. Impure metal acts as anode ( +ve )
    Pure metal acts as cathode ( –ve )
    Metal salt solution act as electrolyte.
  2. Pure metal is deposited at cathode
  3. More reactive metals pass into the solution
  4. Less reactive metals fall at the bottom as ANODE MUD