Concentration Cell
Definition and meaning of Concentration Cell in chemistry.
A concentration cell is a specific type of galvanic cell where both the anode and cathode compartments contain the exact same chemical substances, but at different concentrations. The voltage generated is driven entirely by the natural tendency of the concentrations to equalize.
In more detail
In electrochemistry, most batteries and galvanic cells generate electricity using two completely different metals, relying on the different chemical reactivity of those metals to push electrons through a wire. A concentration cell is unique because it uses the exact same electrodes and the exact same electrolyte solutions in both halves of the cell.
The only difference between the two sides is the molarity of the dissolved ions. The driving force behind a concentration cell is chemical equilibrium. Nature inherently seeks to balance concentrations, driving solutes from areas of high concentration to areas of low concentration.
In the cell, this balancing act cannot happen by simple diffusion because the solutions are separated. Instead, the equalization happens via a redox reaction. Oxidation occurs in the less concentrated half to generate more ions, while reduction occurs in the more concentrated half to consume ions.
As the reaction proceeds, electrons flow from the less concentrated side (the anode) to the more concentrated side (the cathode) through an external wire, generating a measurable electric current. This flow of electricity will continue until the ion concentrations in both compartments become exactly equal.
Once equilibrium is achieved, the voltage of the cell drops to absolute zero, and the battery is completely dead. The voltage produced by a concentration cell is typically very small compared to traditional batteries, but it is highly predictable. Chemists use the Nernst equation to calculate the exact voltage based on the ratio of the two concentrations.
In biology, the principles of the concentration cell are vital for human life; nerve cells in the brain and heart generate the electrical impulses required for thought and movement by maintaining different concentrations of sodium and potassium ions across cell membranes.
Key facts
| Field | Physical Chemistry |
|---|---|
| Components | Identical electrodes and electrolytes |
| Driving Force | Tendency to equalize concentrations |
| Anode (Oxidation) | Less concentrated side |
| Cathode (Reduction) | More concentrated side |
| Voltage Equation | Nernst equation |
By placing two identical copper strips into two copper sulfate solutions of different molarities, the student created a working concentration cell that produced a small voltage.
Frequently asked questions
Why does a concentration cell produce electricity?
The cell produces electricity because the system is trying to reach equilibrium. Electrons flow through the wire to balance the ion concentrations in the two separate compartments.
When does the concentration cell stop working?
The cell dies and the voltage drops to zero the exact moment the ion concentration in the anode side becomes equal to the ion concentration in the cathode side.
What happens at the anode in a concentration cell?
At the anode (the less concentrated side), the solid metal electrode undergoes oxidation, dissolving into the solution as ions to increase the concentration.