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Concentration Cells

The cells whose Description: 31477.png is zero are called concentration cells. This means that the two compartments (cathode and anode) of the electrochemical cell involve same chemical species but the concentrations of the chemical species in the two compartments are different. The concentration cells are of basically two types:
  1. electrode concentration cells and
  2. electrolyte concentration cells.

Electrode concentration cells

In such cells, two similar electrodes at different concentrations/pressures are dipped in the same solution with similar concentration. Let us have an electrochemical cell represented as
 
Pt | H2 (P1 atm) | H+ (c M) || H+ (c M) | H2 (P2 atm) | Pt
 
For the given cell, the reactions occurring are
 
At cathode: Description: 31487.png
 
At anode: Description: 31496.png
 
Net cell reaction: Description: 31503.png
 
Description: 31512.png

Electrolyte concentration cells

In such cells, two electrodes of the same metal are dipped in solutions of metal ions of different concentrations. Let us have an electrochemical cell represented as
 
Pt | H2 (P atm) | HA (c1 M) || HB (c2 M) | H2 (P atm) | Pt
 
In such cells, HA and HB would represent strong acids, if their Ka’s are not given, while they would be weak acids, if their Ka’s are mentioned.
 
For the given cell, the reactions occurring are
 
At cathode: Description: 31521.png
 
At anode: Description: 31529.png
 
Net cell reaction: Description: 31538.png or Description: 31547.png
 
Description: 31554.png




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