[kaoru-m]

I'm a little stumped by one of my homework problems, and I hope some of you could help me get started.

The problem is as follows:

To prepare an aqueous solution of glycerol C3H5(OH)3, in which the mole fraction of the solute is 0.093, what mass of glycerol must you add to 425g of water to make this solution?  What is the molality of the solution?

I realize that I need to find the total # of moles for both the solute and the solution as a whole, but I'm a bit rusty on this. Am I wrong to presume I should just look at the formula for glycerol to find that number?

Any help you could provide is greatly appreciated.

BN

[DevaDevil]

you have the mass of water, so have the number of moles of water.

The fraction will give you the moles of glycerol. and with the molar mass (based on the chemical formula) you have the mass of glycerol.

Molality is moles solute per 1000g solvent.

[kaoru-m]

Thank you!  I for some reason, I wasn't able to set it up properly before.

[AWK]

From definition
molality = moles_of_glycerol / mass_of_water_in_kg

For diluted solutions molarity and molality are practically the same.
For 0.5 M solution an error in molality (or inversely) is of order a few percent. To be more precise you should know a density of molal solution