Transport of Ions
We can begin the discussion of ion equilibria by considering a particularly simple practical instance. Let there be two solutions, say 10 mM and 100 mM potassium chloride, separated by a cation-permeable membrane. The membrane may be made, e.g., of a cation-exchange resin and contain pores lined with fixed negative charges. If the pores are sufficiently narrow and the density of fixed charges high, only potassium ions can move through the membrane from one negatively charged site to another, whereas chloride anions are prevented by electrostatic repulsion from entering the pores. In the absence of an external circuit, connecting the two solutions via electrodes and metallic conductors, the system will achieve an equilibrium with respect to ions. Water will not be in equilibrium, being osmotically driven from the more dilute toward the more concentrated solution; its equilibrium, however, can be easily achieved by applying a suitable hydrostatic pressure to the concentrated solution or adjusting the osmolality of the dilute one with a nonpermeating non-electrolyte.
KeywordsContinuous Layer Electrochemical Potential Sodium Pump Electrical Potential Difference Diffuse Double Layer
Unable to display preview. Download preview PDF.