Raoult's Law

Author:Embibe Experts
JEE Main/Advance
IMPORTANT

Important Questions on Raoult's Law

HARD
IMPORTANT

Two liquids A and B are miscible over the whole range of composition and may be treated as ideal (obeying Raoult's law.) At 350 K the vapour pressure of pure A is 24.0 kPa and of pure B is 12.0 kPa. A mixture of 60% A and 40% B is distilled at this temperature. A small amount of the distillate is collected and and redistilled at 350 K ; what is the mole percent of B in the second distillate ?

EASY
IMPORTANT

The vapor pressure of chlorobenzene and water at different temperatures are

t°C 90 100 110
P°(ϕCl)/mm Hg 204 289 402
P°H2O/mm Hg 526 760 1075

At what temperature will ϕ Cl steam-distillation under a total pressure of 800 mm Hg?

EASY
IMPORTANT

Assuming the formation of an ideal solution, determine the boiling point of a mixture containing 1560 g benzene (molar mass =78 ) and chlorobenzene (molar mass  =112.5 ) using the following against an external pressure of 1000 Torr.

Question Image

EASY
IMPORTANT

Consider two liquids A & B having pure vapour pressures PA°&PB° forming an ideal solution. The plot of 1XAv/s1YA (where XA and YA are the mole fraction of liquid A in liquid and vapour phase respectively) is linear with slope and Y intercepts respectively:

HARD
IMPORTANT

A solution is prepared by mixing 8.5 g of CH2Cl2 and 11.95 g of CHCl3. If vapour pressure of CH2Cl2 and CHCl3 at 298 K are 415 and 200 mm Hg respectively, the mole fraction of CHCl3 in vapour form is: 

EASY
IMPORTANT

The relative lowering of vapour pressure is equal to the mole fraction of the solute. This is the statement of:

HARD
IMPORTANT

For a dilute solution containing 2.5 g.of a non- electrolyte solute. in 100 g of water, the elevation in boiling point at 1 atm pressure pressure is 2°C. Assuming concentration of  solute is much lower than the concentration of solvent, the vapour pressure (mm of Hg )  of the solution is (take Kb=0.76 K kg mol-1 )

MEDIUM
IMPORTANT

At 323 K, the vapour pressure in millimeters of mercury of a methanol-ethanol solution is represented by the equation, p=120XA+140, where XA is the mole fraction of methanol. Then the value of limxA1pXA is:

EASY
IMPORTANT

If P0 and P are the vapour pressures of a solvent and its solution, respectively, and N1 and N2 are the mole fractions of the solvent and non-volatile solute, respectively, then the correct relation is:

MEDIUM
IMPORTANT

The vapour pressure of pure water at 20°C is 17.5 mm Hg. If 18 g of glucose C6H12O6 is added to 178.2 g of water at 20° C, the vapour pressure of resulting solution will be

MEDIUM
IMPORTANT

A very small amount of a non-volatile solute (non-associative, non-dissociative) is dissolved in 100 cm3 of a solvent. At room temperature, vapour pressure of this solution is 98.7 mm of Hg while that of pure solvent is 100 mm of Hg. If the freezing temperature of this solution is 0.72 K lower than that of pure solvent, what is the value of cryoscopic constant of solvent (in K Kg/mol) ? Round off your answer to the nearest whole number. Report your answer as 0 (zero) if you find data insufficient. Given: Molar mass of solvent = 78 g/mol.

EASY
IMPORTANT

Following is false when in a volatile solvent A and a non volatile solute B is mixed (where symbols have their usual meaning):

EASY
IMPORTANT

The vapour pressure of two pure isomeric liquids X and Y are 200 torr and 100 torr, respectively, at a given temperature. Assuming a solution of these components to obey Raoult’s law. The mole fraction of component X in the vapour phase in equilibrium with the solution containing equal amounts of X and Y, at the same temperature, is

MEDIUM
IMPORTANT

Mole fraction of the toluene in the vapor phase which is in equilibrium with a solution of benzene (p° = 120 Torr) and toluene (p° = 80 Torr) having 2.0 mol of each is:

MEDIUM
IMPORTANT

The vapor pressure of a pure liquid A is 40 mmHg at 310 K. The vapor pressure of this liquid in a solution with liquid B is 32 mmHg. Mole fraction of A in the solution, if it obeys Raoult’s law is:

EASY
IMPORTANT

A solution at 20°C is composed of 1.5 mol of benzene and 3.5 mol of toluene. If the vapour pressure of pure benzene and pure toluene at this temperature are 74.7 torr and 22.3 torr, respectively, then the total vapour pressure of the solution and the benzene mole fraction in equilibrium with it will be, respectively:

EASY
IMPORTANT

On mixing heptane and octane form an ideal solution at 373 K, the vapour pressures of the two liquid components (heptane and octane) are 105 kPa and 45 kPa, respectively. The vapour pressure of the solution obtained by mixing 25.0 g of heptane and 35 g of octane will be (molar mass of heptane=100 g mol1 and of octane=114 g mol1)

MEDIUM
IMPORTANT

Two liquids X and Y form an ideal solution. At 300 K, the vapour pressure of the solution containing 1 mol of X and 3 mols of Y is 550 mm Hg. At the same temperature, if 1 mol of Y is further added to the solution, the vapour pressure of the solution increases by 10 mm Hg. Vapour pressure (in mm Hg) of X and Y in their pure states will be, respectively

EASY
IMPORTANT

At 80°C, the vapour pressure of a pure liquid 'A' is 520 mm Hg and that of a pure liquid 'B' is 1000 mm Hg. If a mixture solution of 'A' and 'B' boils at 80°C, at 1 atm pressure, the amount of 'A' in the mixture is (1 atm=760 mm Hg)

MEDIUM
IMPORTANT

A mixture of ethyl alcohol and propyl alcohol has a vapour pressure of 290 mm at 300 K. The vapour pressure of propyl alcohol is 200 mm. If the mole fraction of ethyl alcohol is 0.6, its vapour pressure (in mm) at the same temperature will be