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April 29, 2016

# Homework Help: Chemistry

Posted by Holly on Tuesday, September 25, 2012 at 1:21am.

Ok so reviewing my notes I also got 11,326.6 as the volume in ml. The density of water he wanted us to use was (0.9975) and I went from 1 gal of H2O = 3.785 liters = 3785 grams then multiplied by 3 giving me 11,355g H2O. The only other step I could come up with was using the molality of solute 15.48 mols/kg x 11.355 kg of solvent and working my way back from grams to gallons of ethylene glycol which gave me 0.260 gal. The computer did not like that answer. I'm a little confused on the g/lbs you mentioned in your previous answer.
• Chemistry - DrBob222, Tuesday, September 25, 2012 at 2:16pm

I might point out that 3785 mL is not 3785 g but 3785*0.9975 = 3775 g.
Here is the problem as I worked it. I have rounded here and there but I think all of it is ok in general.
delta T = Kf*m
25.9 = 1.86m
m = 25.9/1.86 = 13.9

3 gallons H2O = 11.356 L
mass = v*d = 11,356 mL x 0.9975 = 11,329 grams = 11.329 kg.

m = mols/kg solvent
mols solute = m*kg solvent = 13.9*11.329 = 157.5 mols solute.

mols solute = grams solute/molar mass solute
g = mols x molar mass = 157.5 x 62.068 = 9787.5 g ethylene glycol.

m = v*d and v = m/d = 9787.5/1.141 = 8578 mL solute.
Convert that to gallons = 2.266 which I would round to 2.27 gallons. I hope this helps you find your trouble.