ABSTRACT
An electrolyte concentration cell involves connecting two identical half-cells via a salt bridge, for example M(s)|M+(aq, a=x)||M+(aq, a=y)|M(s). The only difference in the two half-cells is the difference in ion activity, x and y. The cell reaction is M+(aq, a=y)→M+(aq, a=x) and the Nernst equation is:
as is the same for both half-cells. This reaction also occurs when there is a membrane between the two M+ solutions across which only M+ can transfer. An example is the junction between the inside and outside of a neuron cell membrane, where an imbalance in K+ activity is developed, producing the potential difference Ecell that drives the nerve impulse. The potential is positive in the solution of high M+ concentration and negative in the low M+ solution and is established to increase the rate of transfer from high concentration to low and equalize the M+ activity.
