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>>Calculate the depression in the freezing

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Calculate the depression in the freezing point of water when 10 g of CH

3

CH

2

CHClCOOH is added to 250 g of water.

[Ka=1.4×10

−3

,K

f

=1.86 K kg mol

−1

]

Hard

Updated on : 2022-09-05

Solution

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The molar mass of 2-chloro butanoic acid is 122.5 g/mol.

Number of moles =

122.5

10

=0.0816 mol

Molality of solution =

250

0.0816×1000

=0.3265 m

Let α be the degree of dissociation and c be the initial concentration. The concentration after dissociation is as shown.

c(1−α)

CH

3

CH

2

CHClCOOH

⇌

cα

CH

3

CH

2

CHClCOO

−

+

cα

H

+

The equilibrium constant expression is

K=

c(1−α)

cα×cα

=cα

2

α=

c

K

=

0.3265

1.4×10

−3

=0.065

Calculation of vant Hoff factor:

(1−α)

CH

3

CH

2

CHClCOOH

⇌

α

CH

3

CH

2

CHClCOO

−

+

α

H

+

i=

1

1−α+α+α

=1+α=1+0.065=1.065

The depression in the freezing point ΔT

f

=iK

f

m=1.065×1.86×0.3265=0.647

o

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