tricky collagative concept

[Smooth Operater]

---

Members do not see this ad.

20 gram of an unknown non-volatile substance is dissolved in 1.0 Kg of solvent, and the resulting freezing pt of the solvent is measured and compared to the freezing pt of the pure solvent. In ordeer to calculate the molecular weight of the unknown solvent, what else must be known?

I. the freezing pt depression constant of the solvent
II. the degree to which the solute ionizes in the solvent
III. the density of the resulting solution

I say all 3 are required, but the answer said only I and II are required. I though dentistry of solution is require to convert from molality to molecular weight? am I right?

 

[doc toothache]

The freezing point depression (and other colligative properties) of the solution is proportional to the molal concentration of the solution.

molality= moles of solute/kilogram of solvent

In this example you already know that you have 1 kg of solvent. If the quantity of solvent was given in liters, the density of the solvent[/I] would be needed to calculate the weight of the solvent.

 

[Hyphae]

yup, doc is right. only I & II are needed.

dT F.P. = (Kf)x(m)x(i)