The vapour pressure of pure liquid ' A ' is 70 torr, at 27 ° C . It forms an ideal solution with another liquid ' B ' . The mole fraction of ' B ' is 0 . 2 and total pressure of the solution is 84 torr at 27 ° C . Find the vapour pressure of pure liquid B at 27 ° C .

As we know that, x A + x B = 1 ⇒ x A = 1 - 0 . 2 = 0 . 8 p A ∘ = 70 torr . p ° B = ? p total = 84 torr . From Dalton’s law of partial pressure, p total = p A + p B . . . . . . ( 1 ) From Raoult’s law of vapour pressure, p A = p A ∘ ⋅ x A ⇒ p A = 70 × 0 . 8 = 56 Again, from Raoult’s law of vapour pressure, p B = p B ∘ ⋅ x B p B = p o B × 0 . 2 Substituting these values in equation (1), we have 84 = 56 + 0 . 2 × p o B ⇒ p ° B = 84 − 56 0 .2 = 140 torr . Hence, the vapour pressure of pure liquid B is 140 torr .

An aqueous solution of glucose is made by dissolving 10 g of glucose C 6 H 12 O 6 in 90 g of water at 303 K If the vapour pressure of pure water at 303 K be 32 . 8 mm Hg , what would be the vapour pressure of the solution?

Here, molar mass of glucose ( C 6 H 12 O 6 ) = 180 gm / mol Molar mass of water = 18 gm / mol t So, moles of sugar solute = given mass / molar mass = 10 180 = 0 . 05 mol Moles of solvent water = 90 18 = 5 mol So, mole fraction of solvent = moles of water / moles of solution = 5 5 + 0 . 5 = 0 . 99 Now, we have vapour pressure of solution, P solution = X solvent × P solvent 0 Where, P solvent = pure vapour pressure of solvent (water) = 32 .8 mm Hg (as given) and X solvent = mole fraction of solvent (water) So, P solution = 0 .99 × 32 .8 = 32 .47 mm Hg

Write two differences between ideal and non-ideal solutions.

Ideal solutions : An ideal solution is the solution which obeys Raoult's law perfectly over entire range of concentration and temperature and during its formation there is no change in its enthalpy and volume. Such solutions are formed by mixing the two components which are identical in molecular size, in structure and have almost identical intermolecualr forces. Examples of ideal solution:- Chlorobenzene and bromobenzene; Benzene and toluene; Ethyl bromide and ethyl iodide. Non-ideal solutions : Those solutions which do not obey Rault's law are called non-ideal solutions. Non ideal solutions are formed when the components differ much in their structures and polarities. Non ideal solutions show either positive or negative deviations from Rault's law. Examples of non-ideal solution :- Ethanol and cyclohexane; Acetone and benzene; Water and methanol.

HARD

12th West Bengal Board

IMPORTANT

Earn 100

Vapour pressure of chloroform $({CHCl}_{3})$ and dichloromethane $({CH}_{2} {Cl}_{2})$ at $298 K$ are $200 mm Hg$ and $415 mm Hg$ respectively.
Calculate the vapour pressure of the solution prepared by mixing $25.5 g$ of ${CHCl}_{3}$ and $40 g$ of ${CH}_{2} {Cl}_{2}$ at $298 K$

Important Questions on Solutions

HARD

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 16

Vapour pressure of chloroform

({CHCl}_{3})

and dichloromethane

({CH}_{2} {Cl}_{2})

298 K

are

200 mm Hg

and

415 mm Hg

respectively. Calculate mole fractions of each component in vapour phase.

MEDIUM

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 17

Heptane and octane form an ideal solution at

373 K .

The vapour pressure of the pure liquids at this temperature is

105.2 k Pa

and

46.8 k Pa,

respectively. If the solution contains

25 g

of heptane and

28.5 g

of octane. Calculate vapour pressure exerted by heptane.

MEDIUM

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 17

Heptane and octane form an ideal solution at

373 K .

The vapour pressure of the pure liquids at this temperature is

105.2 k Pa

and

46.8 k Pa,

respectively. If the solution contains

25 g

of heptane and

28.5 g

of octane. Calculate vapour pressure exerted by the solution.

MEDIUM

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 17

Heptane and octane form an ideal solution at

373 K .

The vapour pressure of the pure liquids at this temperature is

105.2 k Pa

and

46.8 k Pa,

respectively. If the solution contains

25 g

of heptane and

28.5 g

of octane. Calculate vapour pressure exerted by the octane.

HARD

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 18

The vapour pressure of pure liquid

' A'

70

torr, at

27 ° C .

It forms an ideal solution with another liquid

' B' .

The mole fraction of

' B'

0.2

and total pressure of the solution is

84

torr at

27 ° C .

Find the vapour pressure of pure liquid

B

27 ° C .

HARD

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 19

An aqueous solution of glucose is made by dissolving

10 g

of glucose

(C_{6} H_{12} O_{6})

90 g

of water at

303 K

If the vapour pressure of pure water at

303 K

32.8 mm Hg,

what would be the vapour pressure of the solution?

HARD

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 20

The vapour pressure of pure benzene at a certain temperature is

0.850 bar .

A non-volatile, non-electrolyte solid weighing

0.5 g

is added to

39.0 g

of benzene (molar mass

78 g {mol}^{- 1}

). The vapour pressure of the solution then is

0.845 bar .

What is the molecular mass of the solid substance?

HARD

12th West Bengal Board

IMPORTANT

NEW SYSTEMATIC MODERN CHEMISTRY>Chapter 2 - Solutions>Follow Up Problems>Q 21

What mass of non-volatile solute, sucrose, need to be dissolved in

100 g

of water to decrease the vapour pressure of water by

30 % ?

Vapour pressure of chloroform CHCl3 and dichloromethane CH2Cl2 at 298 K are 200 mm Hg and 415 mm Hg respectively. Calculate the vapour pressure of the solution prepared by mixing 25.5 g of CHCl3 and 40 g of CH2Cl2 at 298 K

Important Questions on Solutions

Learn and Prepare for any exam you want !

Vapour pressure of chloroform $({CHCl}_{3})$ and dichloromethane $({CH}_{2} {Cl}_{2})$ at $298 K$ are $200 mm Hg$ and $415 mm Hg$ respectively.
Calculate the vapour pressure of the solution prepared by mixing $25.5 g$ of ${CHCl}_{3}$ and $40 g$ of ${CH}_{2} {Cl}_{2}$ at $298 K$