Q. 334.0( 21 Votes )

19.5 g of CH2FCOOH is dissolved in 500 g of water. The depression in the freezing point of water observed is 1.00 C. Calculate the vant Hoff factor and dissociation constant of fluoroacetic acid.

Answer :

Given- w1 = 500g

W2 = 19.5g

Kf = 1.86 K kg mol-1

Molar mass of CH2FCOOH = 12 + 2 + 19 + 12 + 16 + 16 + 1

= 78 g mol-1

The depression in freezing point is calculated by,

ff (where, m is the molality)

f (calculated) = 0.93

To find out the vant Hoff’s factor, we use the formula,


To find out the degree of dissociation α, we use

With degree of dissociation, known to us, we can easily calculate the dissociation constant, Ka using the formula,

Thus, the vant Hoff’s factor is 1.07 an the dissociation constant is 2.634x10-3

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