A beaker is divided by a membrane that is permeable to water and

impermeable to sodium ions. The sodium-water solution on side A is more concentrated than the sodium-water solution on side B. Which of the following statements will be true when equilibrium is reached across the membrane?

a) The absolute number of water molecules will be different on the two sides of the membrane, whereas the final solute concentration will be equal.

b) Equal numbers of water molecules will exist on each side of the membrane at equilibrium.

c) Since the solute can't cross the membrane, the solution will not reach equilibrium.

d) The solute will maintain the original concentration on both sides of the membrane. e) All answers are correct.

a) The absolute number of water molecules will be different on the two sides of the membrane, whereas the final solute concentration will be equal.

Explanation:

According to the concept of osmosis, solvent molecules pass via a semi permeable membrane from area of lower solute concentration to higher solute concentration. Here, solution A and B have different concentration and they are separated by a semi permeable membrane which is only permeable to the water molecules.

Water will move from side B to side A since side B is less concentrated so it has more free water molecules. Eventually, the concentration will become equal on both sides and net movement of water molecules will become zero. However, absolute number of water molecules will be different in both the sides because originally there was more solute in side A so to make the concentration equal, more water molecules will now be present here than side B.