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

HARD

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A solution of $x$ moles of sucrose in 100 grams of water freezes at $- 0.2 ° C$ . Calculate the amount of ice separate out when it is cooled upto $- 0.25 ° C$ :-

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Important Questions on Solutions

MEDIUM

Chemistry>Physical Chemistry>Solutions>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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

HARD

Chemistry>Physical Chemistry>Solutions>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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>Depression in Freezing Point of the Solvent

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})

A solution of x moles of sucrose in 100 grams of water freezes at -0.2°C. Calculate the amount of ice separate out when it is cooled upto -0.25°C:-

Important Questions on Solutions

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A solution of $x$ moles of sucrose in 100 grams of water freezes at $- 0.2 ° C$ . Calculate the amount of ice separate out when it is cooled upto $- 0.25 ° C$ :-