A reverse osmosis cell operates for desalination of water and uses a flat, semipermeable membrane that allows water to pass through and completely retains salt. An aqueous solution of NaCl at CAO concentration flows, under pressure, parallel to the membrane. The ability of the membrane to retain salt gives rise to a salt concentration gradient close to the membrane. The film, of thickness D, where this effect is felt is assumed to be stationary. Determine, from a mass balance for salt, under established regime conditions, the expression that gives the salt concentration at the membrane/solution interface, CAM , when the permeate flux of water through the membrane is N0. Consider the diffusion coefficient of salt in water, (DAB), known and constant. Assume, also, the global concentration ,C, constant.