The osmotic pressure for aqueous solutions of n-dodecylhexaoxyethylene, C12H2s(O

Question

The osmotic pressure for aqueous solutions of n-dodecylhexaoxyethylene, C12H2s(OC2H4)40C2Hs, were measured at 25°C. At concentrations below Co-0.038 g/L no osmotic pressure develops indicating a species is completely permeable across the membrane. Above this concentration an osmotic pressure develops indicating a species is not permeable across the membrane. In the following data, the osmotic pressures are reported for various C - Co values. What is the molecular weight of the species responsible for the osmotic pressure and its second virial coefficient? Explain this phenomena, why is it permeable at low concentrations but not at high concentra- tions? (cm) 1.90 6.53 7.62 10.58 C-Co (g/L) 72 38.12 43.90 58.46

Explanation / Answer

Osmosis is a process that occurs between two containers separated by a semi-permeable barrier. If the barrier has pores large enough to allow water molecules to pass but small enough to block the molecules of a solute, water will flow from the side with the smaller concentration of solute to the side with the larger concentration.

This process continues until either the concentration of solute is equal on both sides or the pressure resisting volume change on the side with the greater concentration exceeds the force driving the water through the barrier. This pressure is osmotic or hydrostatic pressure, and it varies directly with the difference in solute concentration between the two sides.

At low concentration, membrane will allow certain molecules or ions to pass chosen on the basis of size by diffusion .Hence it is permeable at low concentration .At high concentration ,it will not allow to pass ions by diffusion.

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