Sciencemadness Discussion Board

Reverse Osmosis Question

Volitox Ignis - 30-3-2019 at 14:18

In reverse osmosis, pressure is used to force water containing solutes and other undesired impurities through a membrane whose pores are large enough to allow water molecules to pass through, but not large enough to allow the impurities to pass.
Upon being dissolved in water, an ionic compound, like lithium nitrate for instance, dissociates into ions, Li+ and NO3- in this case. Suppose that a solution of a salt were to be subjected to reverse osmosis, but the membrane's pores were large enough to only permit one of the ions through, but not the other. What would happen then? Would the smaller ion simply not go through due to electrical attraction by the larger one?

Metacelsus - 31-3-2019 at 00:34

A voltage gradient across the membrane would form, and eventually an equilibrium would be reached where the chemical potential and electrical potential would cancel. (https://en.wikipedia.org/wiki/Electrochemical_gradient)