Question

A solution containing 16.9 grams of a molecular compound dissolved in 250 grams of water has a freezing point of -0.744 degrees celcius.

Find the molaltity of the solution.
I have -0.744=-1.86*m*i. how do i find i.

what is the gfm of the solute?
I know that the GFM=Mass/moles. So i have 16.9/moles. how do i do that?

Determine the boiling point. how do i do that??

Answer 1

i is the number of particles. Since the problem states that this a molecular compound, then i = 1. That allows you to calculate molality from delta T = kf*m.
Then molality = # mols/kg solvent
molality = # mols/0.250 kg water an this allows you to calculate # mols.
Finally, # mols = g/GFM. You know # mol and g, calculate GFM.

Determine boiling point.
delta T = kb*m
You know molality, you know Kb (or can look it up--I think it's about 0.5 degrees C/m). Then boiling point water is 100 + delta T.
Post your work if you get stuck. Please note the correct spelling of Celsius.

Answer 2

thanks!