Question

An aqueous BSA* solution in the tube on the left is in equilibrium with pure water in the tube on the right. The membrane that separates the two solutions is only permeable to water. When more BSA is added to the solution on the left, .. Why? aqueous BSA pure water A. the water level on the right increases B. the BSA solution level on the left increases C. no change in levels occur *BSA = Bovine serum albumin protein sin H20 permeable membrane National Science Foundation, Shell, CU-EEF & W Department of Chemical & Biological Engineering UNIVERSITY OF COLORADO BOULDER

Answer 1

Option (b) is the correct answer.

This can be explained in this term: Initially the system was at equilibrium so the rate of mass transfer is zero because there is no driving force(i.e. chemical potential of water or concentration is equal at both sides).Now when aqueous solution of BSA is added,we have destroyed the equilibrium by putting some concentration of water on left side and since the membrane is water permeable only so the BSA will not move to the right side.But on the right side we have pure water i.e. at higher concentration while on the left side we have lower concentration i.e. diluted water so their exists a driving force from higher concentration to lower concentration of water.Hence the mass transfer of water will occur to the left side and hence the level in the left column increases.