Question

Lue the term osmotic pressure. What is the advantage of using Osmotic pressure as compared to other colligative properties for the determination of molar masses of solutes in the solutions? Arrange the following solutions in increasing order of their osmotic pressure.
A. ${\text{34}}{\text{.2g/lt sucrose}}$
B. ${\text{60g/lt }}$ of Urea
C. ${\text{90 g/lt}}$ of glucose
D. ${\text{58}}{\text{.5 g/lt}}$ of sodium chloride
Give the reason in support of your answer

Answer 1

Hint: In osmotic pressure instead of molality, molarity of the solution is used, biomolecules are not so stable at higher temperatures thus osmotic pressure can be used for molar mass determination of solutes.

Complete step by step answer:
The vapour pressure of the solution decreases with the addition of non-volatile solute to the volatile solvent and there are many properties of the solutions which cause the decrease in vapour pressure. Some of them are
1. Relative lowering of vapour pressure of solvent
2. Elevation of boiling point of the solvent
3. Depression of freezing point of solvent
4. Osmotic pressure of the solution
All of these properties depend on the number of solute particles irrespective of their nature relative to the total number of particles present in the solution. Such properties are called colligative properties.
The movement of solvent molecules across the semipermeable membrane from pure solvent to the solution is called osmosis and the external pressure applied to stop the movement of solute molecules to solution across the membrane is called osmotic pressure. The osmotic pressure method has got advantages over other colligative properties as the measurement of pressure is around the room temperature and molarity of the solution is used instead of molality.
The order of increase in osmotic pressure is
${\text{NaCl > Urea > Glucose > Sucrose}}$

Additional information:
At a given temperature if two solutions are having the same osmotic pressure, they are called as isotonic solutions. When such solutions are separated by a semipermeable membrane there won’t be the process of osmosis. The solution is said to be hypertonic if the salt concentration is more than 0.9% and if the salt concentration is less than 0.9% it is called a hypotonic solution.

Note: The molar mass of solutes in biomolecules can be determined by osmotic pressure because the biomolecules are usually not stable at higher temperatures and the polymers have got poor solubility.