19.5 g of CH2FCOOH is dissolved in 500 g | Class 12 Chemistry Chapter Solutions, Solutions NCERT Solutions

Question:

19.5 g of CH2FCOOH is dissolved in 500 g of water. The depression in the freezing point of water observed is 1.0°C. Calculate the van't Hoff factor and dissociation constant of fluoroacetic acid.

Answer:

Molecular mass of CH2FCOOH

14 + 19 + 12 + 16 + 16 + 1 = 78 g/mol

Now, Moles of CH2FCOOH = 19.5 / 78

= 0.25

Taking the volume of the solution as 500 mL, we have the concentration:

C = (0.25 / 500) X 1000

Therefore Molality =  0.50m

So now putting the value in the formula :

ΔTf = Kf x m

=1.86 x 0.50 = 0.93K

Van’t hoff factor = observed freezing point depression / calculated freezing point depression

= 1 / 0.93 = 1.0753

 

Let α be the degree of dissociation of CH2FCOOH

Now total number of moles  = m(1-a) + ma +ma = m(1+a)

Or

i = α(1+α) / α = 1 +α  = 1.0753

Therefore α = 1.0753- 1

= 0.0753

Now the Value of Ka is given as:

K= [CH2FCOO-][H+/  CH2FCOOH

(Cα x Cα) / (C (1-α))

= Cα2 / (1-α)

Ka = 0.5 X (0.0753)2  (1-0.0753)

= 0.5 X 0.00567 / 0.09247

= 0.00307 (approx.)

= 3 X 10-3

 

 

 

 

 


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Comments

  • lafo
  • 2019-11-27 00:55:41

Why do we take, K(f) to be 1.86?


  • Subham
  • 2019-06-01 20:48:27

Value of c will be equals to molality


  • Prince bharti
  • 2019-05-28 14:22:10

Great job


  • Prince bharti
  • 2019-05-28 14:21:30

Great job


  • priya
  • 2019-05-24 00:16:29

What a explanation


  • Hets
  • 2019-05-10 00:22:28

How the value of C is calculated for Ka...???


  • Ishan
  • 2019-03-06 16:20:11

C can be calculated by c=n/v


  • Akash shaw
  • 2018-12-18 12:08:20

How the value of 'C' is calculated for Ka value.


  • kandiwali
  • 2017-06-27 18:22:45

Great hard work.


Comment(s) on this Question

Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter . This page offers a step-by-step solution to the specific question from Excercise 2 , Question 33: 19.5 g of CH2FCOOH is dissolved in 500 g of water. The depression in the freezing point of water obs....