Question

If mole fraction of the solvent in a solution decreases then:

• A. vapour pressure of solution increases
• B. boiling point decreases
• C. osmotic pressure increases
• D. all of the above

Answer 1

The correct option is C osmotic pressure increases

Osmosis is the diffusion of a fluid through a semipermeable membrane. When a semipermeable membrane (animal bladders, skins of fruits and vegetables) separates a solution from a solvent, then only solvent molecules are able to pass through the membrane. The osmotic pressure of a solution is the pressure difference needed to stop the flow of solvent across a semipermeable membrane. The osmotic pressure of a solution is proportional to the molar concentration of the solute particles in solution.

$\pi =\frac{nRT}{V}=MRT$

Her,e $\pi$ is osmotic pressure, $R$ is gas constant, $T$ is temperature, $M$ is molarity of solute, $n$ is number of moles of solute present.

When mole fraction of solvent decreases, moles of solvent will decrease and no of moles of solute will increase.

Osmotic pressure is directly proportional to number of moles of solute.

Osmotic pressure will increases with decrease of mole fraction of solvent.

Boiling point will increase with the decrease of mole fraction of solvent.

$\Delta T_b=i.m.K_b$

Vapour pressure will decrease with the decrease of mole fraction of solvent.

$p_A=x_A\times {p_A}^0$