Help with Soltn/Solvent + Molality

[delco714]

THIS MAKES NO SENSE. IT's like starting at Latin.. actually, latin makes more sense... does anyone know about molality, and figuring out all the different stuff, like the mole, and molar mass for this given question?:

 

A 0.517-g sample of a nonvolatile solid solute dissolves in 15.0 g of t-butanol. The freezing point of the solution is 22.7ºC.

 

a. What is the molality of the solute in the solution

b, Calculate the molar mass of the solute.

 

(BTW: t-butanol>> Freezing point = 25.5 C, Kf = ( (C*kg) / mole) = 9.1)

 

If you can explain how you do it... pleeeassee. I have no idea how to do this.. The lab book doesn't tell us how, it just throws us numbers and questions. This is an important inorg. chem concept and I do want to learn how to do it!!

[Riogho]

Molality is Moles of solute / kg of solvent.

 

Do you remember learning Raoult's Law? It had a little something talking about the Kf and freezing point that directly relates to molality.

 

http://en.wikipedia.org/wiki/Raoult%27s_law