A solution containing 18 g from a non-volatile solute in 200 g of H 2 O freezes at 272 . 07 K . Find the molecular mass of the solute. ( K f = 1 . 86 K m - 1 )

Given: The weight of water, W 1 = 200 g The weight of the solute, W 2 = 18 g Molal freezing point depression constant, K f = 1 . 86 K m - 1 The freezing point of the solution is = 272 . 07 K Depression in freezing point ∆ T f = 273 - 272 . 07 = 0 . 93 K If the molecular mass of the solute is M 2 then, M 2 = K f × W 2 × 1000 ∆ T f × W 1 M 2 = 1 . 86 × 18 × 1000 0 . 93 × 200 M 2 = 180 g / mol

EASY

Earn 100

When acetic acid is dissolved in benzene, it shows an increase in molecular weight. How many times does it increase, than that of actual molecular weight of acetic acid?

50% studentsanswered this correctly

Important Questions on Solutions

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

The freezing point of a

4 %

aqueous solution of

X

is equal to the freezing point of a

12 %

aqueous solution of

Y

. If the molecular weight of

X

A

, then the molecular weight of

Y

will be

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

The vapour pressure of acetone at

20^{o} C

185 torr

. When

1.2 g

of a non-volatile substance was dissolved in

100 g

of acetone at

20^{o} C

, its vapour pressure was

183 torr

. The molar mass

(g m o l^{- 1})

of the substance is:

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Solution of

' A'

containing

3 \cdot 42 g

of it in

100 {cm}^{3}

of water is found to be isotonic with a

6.84 %

(W / v)

solution of sucrose, what is the molar mass of '

' A' ?

(at. wt;

C = 12, H = 1, 0 = 16

)

EASY

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Give reasons for the following:
Elevation of boiling point of

1 M KCl

solution is nearly double than that of

1 M

sugar solution.

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

A non-volatile solute,

{}^{'}A^{'}

tetramerises in water to the extent of

80 %

2.5 g

{}^{'}A^{'}

100 g

of water, lowers the freezing point by

0.3 ° C

. the molar mass of

A

g {mol}^{- 1}

is (

K_{f}

for water

= 1.86 K kg {mol}^{- 1}

)

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Acetic acid dimerises when dissolved in benzene. As a result boiling point of the solution rises by

0.36 ° C,

when

100 g

of benzene is mixed with

X g

of acetic acid. In this solution, if experimentally measured molecular weight of acetic acid is

117.8

and molar elevation constant of benzene is

2.57 K kg {mol}^{- 1},

what is the weight

%

and degree of dissociation (in

%

) of acetic acid in benzene?

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

The boiling point of benzene is

353.23 K

. When

1.80 g

of non-volatile solute was dissolved in

90 g

of benzene, the boiling point of is raised to

354.11 K

. Calculate the molar mass of the solute. (

K_{b}

for benzene is

2.53 K Kg {mol}^{- 1}

)

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

A solution containing

18 g

from a non-volatile solute in

200 g

H_{2} O

freezes at

272.07 K

. Find the molecular mass of the solute.

({K_{f}}^{} = 1.86 K m^{- 1})

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

When the same amount of the solute

' P'

and

' Q'

are separately dissolved in

500 g

water, the

Δ

T_{f}

values are

0.15 K

and

0.30 K

respectively. If the molecular weight of

{}^{'}P^{'}

80 g {mol}^{- 1}

, then the molecular weight of

{}^{'}Q^{'}

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

58.5 g of NaCl and 180 g

of glucose were separately dissolved in

1000 mL

of water. Identify the correct statement regarding the elevation of boiling point (b.pt.) of the resulting solutions.

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Give reasons for the following:
Measurement of osmotic pressure method is preferred for the determination of molar masses of macromolecules such as proteins and polymers.

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Determination of the molar mass of acetic acid in benzene using freezing point depression is affected by:

HARD

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Calculate the mass of ascorbic acid

(Molar Mass = 176 g {mol}^{- 1})

to be dissolved in

75 g

of acetic acid, to lower its freezing point by

1 . 5^{°} C

(K_{f} = 3.9 K kg {mol}^{- 1})

EASY

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

An aqueous solution containing

1.0 g

of urea boils at

100.25 ° C .

The aqueous solution containing

3.0 g

of glucose in the same volume will boil at:

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Visha took two aqueous solutions — one containing 7·5 g of urea (Molar mass = 60 g/mol) and the other containing 42·75 g of substance Z in
100 g of water, respectively. It was observed that both the solutions froze at the same temperature. Calculate the molar mass of Z.

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

A solution is prepared by dissolving $9.25 g$ of non-volatile solute in $450 mL$ of water. It has an osmotic pressure of $350 mm$ of $Hg$ at $27 ° C$ . Assuming the solute is non-electrolyte, determine its molecular mass. ( $R = 0.0821 L atm K^{- 1} {mol}^{- 1}$ ).

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

A $5 %$ solution of non-volatile solute in water has vapour pressure $745 mm$ of $Hg$ at $373 K$ . Calculate the molar mass of the solute.

Given vapour pressure of pure water at $373 K$ is $760 mm$ of $Hg$ .

MEDIUM

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

8 g

of a non-electrolyte solute is dissolved in

114 g

n -

octane to reduce its vapour pressure to

80 %,

the molar mass (in

g {mol}^{- 1}

) of the solute is [Given that molar mass of n-octane is

114 g {mol}^{- 1}

]

EASY

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

In 108 g of water, 18 g of a non-volatile compound is dissolved. At

100^{o} C

the vapor pressure of the solution is 750 mm Hg. Assuming that the compound does not undergo association or dissociation, the molar mass of the compound in

g m o l^{- 1}

HARD

Chemistry>Physical Chemistry>Solutions>Van't Hoff's Factor

Molecules of benzoic acid

(C_{6} H_{5} COOH)

dimerise in

30 g

of benzene. '

w

g

of benzoic acid shows a depression in freezing point equal to

2 K

. If the percentage association of the acid to form dimer in the solution is

80

, then

w

is:

(

Given that

K_{f} = 5 K kg {mol}^{- 1}

, molar mass of benzoic acid

= 122 {gmol}^{- 1})

When acetic acid is dissolved in benzene, it shows an increase in molecular weight. How many times does it increase, than that of actual molecular weight of acetic acid?

Important Questions on Solutions

Learn and Prepare for any exam you want !