Cells with identical electrodes differing only in concentration, producing voltage from dilution tendency.
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A concentration cell has identical electrodes and electrolytes on both sides that differ only in concentration, so its standard potential is zero and its voltage arises entirely from the concentration ratio. The potential is E = -(0.0592/n) log Q, and electrons flow in the direction that reduces the concentrated side and oxidizes the dilute side, tending to equalize the concentrations. The principle matters in pH electrodes, where internal and external hydrogen ion concentrations differ, and in biological membranes, where nerve signals depend on ion concentration differences. Concentration cells show that electrochemical driving force can arise from dilution alone.
Key ideas: Both half-cells use the same electrode and ion but at different concentrations, so E standard is 0 and E = (0.0592/n) log10(C_conc/C_dil) at 25 C, with the concentrated side as cathode. Current flows until both concentrations equalize. Example: Cu2+ at 1.0 M versus 0.010 M with n = 2 gives 0.059 V.
Common mistakes and connections: Mistake: assuming E standard is nonzero, or putting the concentrated side at the anode (the concentrated side is the cathode, because it is reduced and becomes more dilute). Used to measure Ksp, pH and ion activity, and as a model for membrane potentials in nerve cells.
A concentration cell has E0 = 0 and its voltage comes only from the concentration ratio, falling to zero as the two sides equalize (about 0.059 V per tenfold for n = 1). The interactive lesson shows this as a live animation or chart.
Cu∣0.01 M Cu2+‖1 M Cu2+∣Cu gives about 0.059 V at 25 C, with the concentrated side reduced.
Cells with identical electrodes differing only in concentration, producing voltage from dilution tendency.
Concentration Cells is a advanced topic in Acids, Bases & Electrochemistry. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Acids, Bases & Electrochemistry first: Nernst Equation, Cell Potential and Free Energy, Cell Potential and Equilibrium.
The next topics in Acids, Bases & Electrochemistry are Faraday's Constant and Faraday's First Law.
Yes. The interactive lesson includes a self-check question on Concentration Cells, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Concentration Cells is topic 58 of 105 in Acids, Bases & Electrochemistry.