BE.011/2.772 Problem Set 3 Due March 3, 2004 1. Dialysis is common laboratory procedure used to remove low molecular weight solutes from protein solutions. Example situations include: removal of removal of free, unreacted label after fluorescently labeling a protein; and removal of urea from a denatured protein solution to allow refolding of the protein. The protein solution is sealed inside a dialysis bag or tubing and placed in container with a large excess of pure water, as shown in the figure. The system is then allowed to come to equilibrium. For this problem, consider an idealized system where the only solute in the dialysis bag is the low molecular weight solute (i.e., no protein is actually present.) (a) Explain why the combined system of the protein solution (system “A”) and the water (system “B”) may be considered to be an isolated system. (b) Use a lattice model, with each individual water molecule occupying a single site in the lattice, to show that the entropy of System B is zero at the start of the experiment. Designate
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