Concentration Cells

(or concentration circuits), a type of galvanic element. A distinction is made between concentration cells with and without ion transfer.

Concentration cells with ion transfer are produced by the immersion of two identical electrodes (for example, silver electrodes) in a tank divided by a semipermeable partition and containing the same electrolytic solution (for example, silver nitrate) on both sides of the partition, but in different concentrations. In such concentration cells the electromotive force (emf) arises as a result of direct transfer of the electrolyte from the more concentrated solution to the less concentrated solution. In concentration cells of the second type the concentration of the electrolyte is equalized as a result of chemical processes taking place on two dissimilar electrodes. An example of a concentration cell without ion transfer is a cell with platinum and silver electrodes immersed in a hydrochloric acid solution. For the same ratio of electrolyte concentration the emf of a concentration cell without ion transfer is twice that of a cell with ion transfer. Concentration cells are used in measuring activity coefficients and transference numbers.