delta T = i*Kf*m
1.2 = 1*1.86*m
Solve for m = molality.
Then molality = moles/kg solvent = moles/0.130 kg
Solve for moles.
Then moles = grams/molar mass.
Plug in for moles from above and grams from the problem and solve for molar mass.
Round to two significant figures. Post your work if you get stuck.
An aqueous solution containing 32.9 g of an unknown molecular (nonelectrolyte) compound in 130.0 g of water has a freezing point of -1.2 ∘C.
Calculate the molar mass of the unknown compound.
Express your answer using two significant figures.
Please help, thank you.
4 answers
Im sorry I still have no idea how to do this.
1.2 = 1*1.86*m
= 1.2 = 1.86*m
1.2/1.86 = 0.645... m
Molality = 0.64
But multiply it by 0.13 and you get 0.084 and I know thats too low
1.2 = 1*1.86*m
= 1.2 = 1.86*m
1.2/1.86 = 0.645... m
Molality = 0.64
But multiply it by 0.13 and you get 0.084 and I know thats too low
waiiiit, did you mean 32.9/130 = 0.253 ???
Your first step was right. m = 0.645 but I would have kept all the numbers until finishing before rounding anything.
Your second step was right. moles = 0.0839 but I didn't round off. Your error is that is NOT the end of the problem. The number of moles = 0.0839. I had another step.
mols = grams/molar mass
0.0839 = 32.9/molar mass or molar mass = 32.9/0.0839 = 392 which when rounded to two significant figures is 390. Your mistake? Apparently you equation # mols (that 0.0839 as the molar mass. It isn't. You just didn't do the last step. I would be interested in knowing why. Please tell me what about my three-step solution confused you. Good luck.
Your second step was right. moles = 0.0839 but I didn't round off. Your error is that is NOT the end of the problem. The number of moles = 0.0839. I had another step.
mols = grams/molar mass
0.0839 = 32.9/molar mass or molar mass = 32.9/0.0839 = 392 which when rounded to two significant figures is 390. Your mistake? Apparently you equation # mols (that 0.0839 as the molar mass. It isn't. You just didn't do the last step. I would be interested in knowing why. Please tell me what about my three-step solution confused you. Good luck.