Question

Define osmotic pressure and reverse osmosis. Define how molecular mass of a substance can be determined on the basis of osmotic pressure.

Answer 1

Hint: Reverse osmosis is the basis of filtering and osmotic pressure is the colligative property which is dependent upon the concentration of the solute particles present in solution.

Complete step by step answer:
Osmotic pressure can be defined as the minimum pressure that must be applied to a solution to halt the flow of solvent molecules. This property is dependent upon the concentration of the solute particles present in solution and hence is one of the colligative properties.
It can be calculated by the following formula:
${\rm{\pi }} = {\rm{iCRT}}$
Where,
${\rm{\pi }}$is osmotic pressure
i is the van’t Hoff factor
C is the molar concentration of the solute in the solution
R is the universal gas constant
T is the temperature.
If we see, basically osmosis refers to the movement of the solvent molecules through the semipermeable membrane from a region where the concentration of the solute is low to the region where the concentration of solute is high and eventually equilibrium is established to the both sides resulting in the same concentration on the both sides. Osmosis is the special case of the diffusion.
Now if we discuss reverse osmosis, It is the process by which solvent passes through the semipermeable membrane in the opposite direction to that of natural osmosis. Reverse osmosis is the water purification process which removes ions, unwanted molecules and larger particles from drinking water.
${\rm{\pi }} = \,\dfrac{{{n_B}}}{V}RT$
Where,
nB is moles of the solute
V is volume of the solution
If WB grams of solute whose molecular mass is MB is present in the solution then,
If we know the value of WB, T , ${\rm{\pi }}$and V then we will be able to determine the value of MB .
${M_B} = \,\dfrac{{{W_B}RT}}{{\pi V}}$
Molecular mass of a substance can be determined on the basis of osmotic pressure by various processes like using Barkley and Hartley’s apparatus.

Note: Equation which is used to calculate the osmotic pressure only holds true for the solutions that behave like ideal solutions. One of the disadvantages of purification of water by the reverse osmosis process is that sometimes with unwanted ions, the good ions also get removed which is basically needed by our body.