Osmosis related question

Question

The reason for osmosis is :-

 

(1) The vapour pressure of solvent is less than that of solution

(2) The vapour pressure of solution is less than that of solvent

(3) Movement of solvent molecules from solvent side to solution

(4) Movement of solute molecules form solution side to solvent

Answer 1

In osmosis, solvent molecules move from the solvent side of a membrane to the solution side of the membrane. 

 

This is because the relative rate of solvent molecules passing through the membrane is related to their mole fraction - on the pure solvent side the mole fraction is 1.00 or 100% solvent molecules, so they will want to go through the membrane to the other side based on natural entropy and migration.  But on the solution side, there are solute particles that reduce the relative number of solvent molecules.  Thus, the rate of migration through the membrane in the other direction (from the solution to the pure solvent side) is slower. 

 

Overall the solvent molecules will migrate toward the solution until the rates of osmosis both directions through the membrane are equal (solution is infinitely diluted, it will have no osmotic pressure).