MyQuestionIcon

1

You visited us 1 times! Enjoying our articles? Unlock Full Access!

Relationship between Vapor Density & Relative Molecular Mass

The vapour pr...

Question

The vapour pressure of pure water at $30^{\circ} C$ is $31.50 mm Hg$ . When 3.0 g of a non-volatile solute was dissolved in 54 g of water, the vapour pressure of the solution was found to be $31.30 m m H g$ . Calculate the molar mass of the solute.

Open in App

Solution

Given : $P_{A}^{o} = 31.50 m m H g, P_{A} = 31.30 m m H g,$
$W_{B} = 3.0 g, W_{A} = 54 g, M_{B} = ?$
$M_{A} = 2 \times 1 + 16 = 18 g / m o l$
$\frac{P_{A}^{o} - P_{A}}{P_{A}^{o}} = X_{B} = \frac{\frac{W_{B}}{M_{B}}}{\frac{W_{A}}{M_{A}} + \frac{W_{B}}{M_{B}}}$
$\Rightarrow \frac{31.50 - 31.30}{31.50} = \frac{3 / M_{B}}{\frac{54}{18} + \frac{3}{M_{B}}}$
$\Rightarrow \frac{0.20}{31.50} = \frac{(3 / M_{B}) \times (18 M_{B})}{54 M_{B} + 18 \times 3}$
$\frac{54}{54 M_{B} + 54} = \frac{1}{M_{B} + 1} = \frac{0.20}{31.50}$
$0.20 (M_{B} + 1) = 31.50 \times 1$
$0.20 M_{B} + 0.20 = 31.50$
$0.20 M_{B} = 31.50 - 0.20 = 31.30$
$M_{B} = \frac{31.30}{0.20} = 156.5 g/mol$

Suggest Corrections

thumbs-up

3

Similar questions

Q. A solution is prepared by dissolving 10 g of non-volatile solute in 200 g of water. It has a vapour pressure of 31.84 mm Hg at 308 K. Calculate the molar mass of the solute.
(Vapour pressure of pure water at 308 K = 32 mm Hg).

5.8 g

of non volatile solute was dissolved in 100 g of carbon disulphide

(C S_{2})

. The vapour pressure of the solution was found to be 190 mm. of Hg. Calculate the molar mass of the solute given the vapour pressure of pure

C S_{2}

is 195 mm. of Hg [Molar mass of

C S_{2} = 76 g m o l^{- 1}

Q. 10 g of a certain non-volatile solute was dissolved in 100 g of water at

20^{o} C

. The vapour pressure was lowered from 17.3555 to 17.235 mm. Calculate the molecular mass of the solute.

Q. 5.8 g of a non-volatile solute was dissolved in 100g of carbon disulphide

(C S_{2})

. The vapour pressure of the solution of the solution was found to be 190 mm of Hg. Calculate molar mass of solute given the vapour pressure of

(C S_{2})

is 195 mm of Hg.
[molar mass of

(C S_{2})

^{- 1}

Q. A solution containing

30 g

of a non-volatile solute in exactly

90 g

water has a vapour pressure of

21.85 m m H g

25^{\circ} C

. Further 18 gm of water is then added to the solution. The resulting solution has a vapour pressure of 22.18 mmHg at

25^{\circ} C

. Calculate (a) molar mass of the solute, and (b) vapour pressure of water at

25^{\circ} C

.

View More

Join BYJU'S Learning Program

similar_icon

Related Videos

lock

Introduction

CHEMISTRY

Watch in App

explore_more_icon

Explore more

Relationship between Vapor Density & Relative Molecular Mass

Standard X Chemistry

Join BYJU'S Learning Program

CrossIcon