Tuesday, July 12, 2011

Chemistry Form 4: Chapter 6 - Daniell Cell

Daniell cell is also known as Galvanic cell which using same working principle as voltaic cell. It converts chemical energy to electrical energy. Daniell cell is a part of a battery consisting of two metals joined by a salt bridge or a porous pot.

  • More electropositive metal acts as negative terminal which undergoes oxidation process (release electron)
  • Less electropositive metal acts as positive terminal which undergoes reduction (gain electron).
  • Electron flow from negative terminal to positive terminal.
  • The function of salt bridge or porous pot is to allow the movement of ions to pass through it to complete electrical circuit. Another function is to separate two electrolyte solutions. 
  • Examples of salt bridge are sodium chloride or potassium nitrate.

At Negative Terminal: More electropositive metal ( Zinc )

Observation:  Zinc plate dissolves or becomes thinner, its mass decreases
Half chemical equation :     Zn  ------>     Zn2+   +    2e

At Positive Terminal: Less electropositive metal ( Copper )
Observation:  Copper plate becomes thicker
Half chemical equation :     Cu2+     +    2e   ------>    Cu

Click on the diagram below to play!


Anonymous said...

could you explain, why the less electropositive electrode undergoes reduction process?

Anonymous said...

electropositive is the tendency of an element to release electrons. when an element is less electropositive, it is harder for it to release any electrons compared to more electropositive element. rememeber, more electropostitive means HIGHER tendency to release electrons. therefore, the less electropositive element will receive the electrons. when this happens, the element is reduced because it gains electrons from the more electropositive element. :)