Analyzing a Donnan equilibrium

Suppose that two equal volumes of 0.200 m NaCl(aq) solution are separated by a membrane and that the left-hand side of the experimental arrangement contains a polyelectrolyte Na P at a concentration of 50 g dm . Assuming that the membrane is not permeable to the polyanion, which has a molar mass of 55 kg mol , calculate the molar concentrations of Na and Cl in each compartment. 

Strategy We saw above that the sum of the equihbrium concentrations of Na+ in both compartments is 

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