# Chemistry Class 12 NCERT Solutions: Chapter 2 Solutions Part 14

Q: 33. of is dissolved in of water. The depression in the freezing point of water observed is . Calculate the van't Hoff factor and dissociation constant of fluoroacetic acid.

Answer:

It is given that:

We know that:

Therefore, observed molar mass of

The calculated molar mass of is:

Therefore, van’t Hoff factor,

Let α be the degree of dissociation of

Now, the value of is given as:

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

Therefore,

Q: 34. Vapour pressure of water at 293 K is 17.535 mm Hg. Calculate the vapour pressure of water at 293 K when 25 g of glucose is dissolved in 450 g of water.

Answer:

Vapour pressure of water, of Hg

Mass of glucose,

Mass of water,

We know that,

Molar mass of glucose

Molar mass of water,

Then, number of moles of glucose,

And, number of moles of water,

We know that,

Hence, the vapour pressure of water is of Hg.