# chem

posted by on .

delta T = Kf*molality
Plug in 5.00 C for delta T, 1.86 for Kf and calculate molality.
Then molality x kg solvent x molar mass = grams.
You know molality, kg solvent, and molar mass. Calculate grams.

molar mass? where did u got the molar mass from ?

• chem - ,

You want grams, don't you?
The formula I have came from this.
molality = mols/kg solvent. Solve for mols.
mols = molality x kg solvent.

mols also = grams/molar mass
so we set mols = mols

so molality x kg solvent = g/molar mass
multiply both sides by molar mass an we have
molality x kg solvent x molar mass = grams.
You didn't copy your question but it was something with an OH on/in it. That's what you want the molar mass of. I think I remember the question as being determine the mass of the material to make the freezing point decrease to -5.00 C.

• chem - ,

That's ethylene glycol

• chem - ,

No. I went back and reread the problem. It asks for mols, not grams.
so molality = mols/kg solvent and this can be rearranged to
molality x kg solvent = mols
You know m and you know kg solvent. Solve for mols.