12 gm of a solid solute is dissolved in 90 gm pure water. Vapour pressure of the resulting solution is 750 mm Hg at 100 o C temperature. Calculate molecular mass of the solute. (Solute does not undergo any dissociation or association in its aqueous solution).

According to raoult's law, p ∘ - p p ∘ = w × M m × W p ∘ is Vapour pressure of pure water p is vapour pressure of solvent w is weight of solute m is molecular weight of solute W is weight of solvent M is molecular weight of solvent 760 - 750 760 = 12 × 18 m × 90 m = 12 × 18 × 760 10 × 90 = 164160 900 m = 182 . 4 Therefore, molecular mass of the solute = 182 . 4 g

Raoult's law: According to this law, the partial pressure of any volatile constituents of a solution at a constant temperature is equal to the vapour pressure of pure constituents multiplied by the mole fraction of that constituent in the solution. For liquid-liquid solution: Let a mixture (solution) be prepared by mixing n A moles of liquid A and n B moles of li quid B . Let P A and P B be the partial pressures of two constituents A and B in solution and P A 0 and P B 0 the vapour pressures in pure state respectively. Thus, according Raoult's law, P A = X A P A 0 and P B = X B P B 0 .

MEDIUM

Earn 100

State Raoult's law. Derive its mathematical expression for a solution of the non-volatile solute in a volatile solvent.

Important Questions on Solutions

EASY

Chemistry>Physical Chemistry>Solutions>Raoult's Law

What is Raoult's law? Give its two limitations.

HARD

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct? Assume that the temperature is constant at

25^{o} C

. (Given vapour pressure data at

25^{o} C

, benzene = 12.8 kPa, toluene = 3.85 kPa)

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

For ethanol-acetone mixture solute-solvent interaction is weaker than solute-solute and solvent-solvent interaction. Does this solution obey Raoult's law ?

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Mixing acetone and chloroform occurs with reduction in volume. Name the type of deviation from Raoult's law shown by the above mixture and state whether the process is endothermic or exothermic.

HARD

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Liquids

A

and

B

form an ideal solution in the entire composition range. At

350 K,

the vapour pressure of pure A and pure B are

7 \times 10^{3} Pa

and

12 \times 10^{3} Pa

, respectively. The composition of the vapour in equilibrium with a solution containing 40 mole percent of A at this temperature is:

EASY

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Draw a graph depicting the deviation from Raoult's law exhibited by a solution prepared by mixing ethanol and acetone.

HARD

Chemistry>Physical Chemistry>Solutions>Raoult's Law

State Raoult's law. How is the molecular mass of a solute determined from lowering of vapour pressure measurement?

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

A mixture of toluene and benzene boils at

100^{o} C

. Assuming ideal behaviour, the mole fraction of toluene in the mixture is closest to [Vapour pressures of pure toluene and pure benzene at

100^{o} C

are

0.742

and

1.800

bar respectively. 1 atm

= 1.013

bar]

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

State Raoult’s law for a solution containing volatile components. Write two characteristics of the solution which obeys Raoult’s law at all concentrations.

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Show that total vapour pressure over the solution ot two liquids

1

and

2

at a particular temperature varies linearly with the mole fraction of a component.

HARD

Chemistry>Physical Chemistry>Solutions>Raoult's Law

A plot of vapor pressure vs. mole fraction for a solution comprising two components $A$ and $B$ is shown below. Which of the following is CORRECT?

Question Image

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Vapour pressure of water at

293 K

17.535 mm Hg

. Calculate the vapour pressure of water at

293 K

when

25 g

of glucose is dissolved in

450 g

of water.

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

The vapour pressures of pure liquids

X

and

Y

350 K

are

200 mm

and

300 mm

Hg

respectively. Then the correct vapour pressure (in

mm

Hg

) of an ideal solution containing

X

and

Y

in the mole ratio

3 : 2

at the same temperature is

HARD

Chemistry>Physical Chemistry>Solutions>Raoult's Law

12 gm

of a solid solute is dissolved in

90 gm

pure water. Vapour pressure of the resulting solution is

750 mm Hg

100^{o} C

temperature. Calculate molecular mass of the solute. (Solute does not undergo any dissociation or association in its aqueous solution).

HARD

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Liquids A and B form ideal solution over the entire range of composition. At temperature

T

, equimolar binary solution of liquids A and B has vapour pressure

45 T o r r

. At the same temperature, a new solution of A and B having mole fractions

x_{A} and x_{B}

, respectively, has vapour pressure of

22.5 T o r r

. The value of

\frac{x_{A}}{x_{B}}

, in the new solution is ____.

(Given that the vapour pressure of pure liquid A is

20 Torr

at temperature

T

)

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

For a solution formed by mixing liquids

L

and

M

, the vapour pressure of

L

plotted against the mole fraction of

M

in solution is shown in the following figure, Here,

X_{L}

and

X_{M}

represent mole fractions of

L

and

M

, respectively, in the solution. The correct statement(s) applicable to this system is(are) -

Question Image

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

A solution is prepared by mixing

8.5

g of

{CH}_{2} {Cl}_{2}

and

11.95 g

{CHCl}_{3}

. If vapour pressure of

{CH}_{2} {Cl}_{2}

and

{CHCl}_{3}

298

K are

415

and

200

mm Hg respectively, the mole fraction of

{CHCl}_{3}

in vapour form is:

(M o l a r m a s s o f Cl = 35.5 g m o l^{- 1})

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

Vapour pressure of benzene is

200 mm Hg

. When

2 g

of non-volatile solute is dissolved in

78 g

benzene, benzene solution has vapour pressure

195 mm Hg

. Calculate the molar mass of the solute in

{gmol}^{- 1}

( molar mass of benzene =

78 {gmol}^{- 1}

EASY

Chemistry>Physical Chemistry>Solutions>Raoult's Law

State Raoult's law.

MEDIUM

Chemistry>Physical Chemistry>Solutions>Raoult's Law

A solution at

20^{o} 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:

State Raoult's law. Derive its mathematical expression for a solution of the non-volatile solute in a volatile solvent.

Important Questions on Solutions

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