[KnightDoc2015]

1. Which of the following solutions would have the highest boiling point?  Solution 1 is made with 8.709 g of potassium sulfate in 250 mL of water.  Solution 2 is made with 15.95 g of copper(II) sulfate in 1000 mL of water. Solution 3 is made with 1.458 g of hydrogen chloride in 200 mL of water (becomes hydrochloric acid when aqueous.
NOTE: Do NOT assume the limiting factor for any ionic solution(s) made in this problem.  All the information needed for this problem is not given.  When using any constants or “factors” make sure you relate them to their exact concentration.


** I know that you need to use Delta (T) = kmi where k is the constant for water at the boiling point, m is the molality and i is the van't hoff factor. The part that is tripping me up is the fact I have to research the correct van't hoff factor based on its molality...not just assumed based on how many ions it disassociates into due to reassociation. So if anyone can find these factors and work out the problem and see if we get the same answer I would be SP THANKFUL!

 
A. solution of potassium sulfate                  B. solution of copper(II)sulfate
C. solution of hydrogen chloride              
D. both the solutions of copper(II)sulfate and hydrogen chloride have the highest boiling points
E. both the solutions of potassium sulfate and hydrogen chloride have the highest boiling points

[Arkcon]

You can start by computing the molality in each case anyway.  One may be so high that the answer may scream at you, or you could at least exclude one.  This is a trick you'll need during an exam, when time may be an issue.

[KnightDoc2015]

Yes, I calculated the molalities: solution 1 and 3 both have 0.2m and solution 2 has a 0.1m. I just can't seem to confirm the van't hoff factors associated with the solutes at their respected concentrations. I know for sure that the van't hoff factor is 2.17 for K2SO4, 1.12 for CuSO4, and somewhere between 1.9 and 2 for HCl. If my calculations are correct, K2SO4 should have the highest but I just wanted to double check and make sure I did this correctly...

Thank you!!

[vanthoff]

Where did you get the 1.12 for CuSO4 and 2.17 factors

I can't find anything verifying them.

[KnightDoc2015]

I just googled it. We can't assume that it will perfectly disassociate bc there's always some reassociation depending on the concentration (molality). I found a chart that stated van't hoff factors to the concentration and that's where I got those numbers. I checked them with my professor and he agreed those were correct. But he only said HCL is somewhere between 1.9 and 2. However, I calculated each temp change and I don't think it affects the problem if you use 1.9 or 2. When you order them from least to greatest, it's still the same. I got HCl < CuSO4 < K2SO4

Has anyone calculated this with the van't hoff factors I provided and got the same order I did?