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

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Academic session 2026-27, Chapter 1 in the current curriculum.

Welcome to the NCERT Solutions for Class 12 Chemistry - Chapter Solutions. This page offers a step-by-step solution to the specific question from Exercise 2, Question 33:

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.

. With detailed answers and explanations for each chapter, students can strengthen their understanding and prepare confidently for exams. Ideal for CBSE and other board students, this resource will simplify your study experience.

Question 33:

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:

Ka  = [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
  • Nov 27, 2019

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


  • Subham
  • Jun 01, 2019

Value of c will be equals to molality


  • Prince bharti
  • May 28, 2019

Great job


  • Prince bharti
  • May 28, 2019

Great job


  • priya
  • May 24, 2019

What a explanation


  • Hets
  • May 10, 2019

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


  • Ishan
  • Mar 06, 2019

C can be calculated by c=n/v


  • Akash shaw
  • Dec 18, 2018

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


  • kandiwali
  • Jun 27, 2017

Great hard work.


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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....

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