Question

Im not looking for answers. I'm looking for guidance or explanations.. here is my question:

Match the following aqueous solutions with the appropriate letter from the column on the right.


1. 0.21 m CuSO4 A. Highest boiling point

2. 0.15 m MnCl2
B. Second highest boiling point

3. 0.13 m CaBr2
C. Third highest boiling point

4. 0.36 m Sucrose(nonelectrolyte)
D. Lowest boiling point


I know that the boiling point of a solution increases with the number of dissolved particles. But how do you determine that..? Thanks

Answer 1

Well the number of dissolved particles for a solution is determined by how many ions a certain compound will dissociate into. For example NaCl will dissociate in water releasing 2 ions. CaBr2 dissociates into 3 ions in water.
Boiling point elevation can be described by
\[\Delta T_b=K_b(m)(i)\]
you can ignore K_b for this question as it is unchanged.
m being the molality and i being Van Hoff's Factor (which represent the number of particles in solution)

Answer 2

So for example looking at choice A.
You would say 2*(.21m) = .42m

Answer 3

This is because CuSO4 dissociates into 2 ions in water. So you multiply the molality by 2.

Answer 4

okay so.. for a different one. (NH4)2SO4.. it would have.. 12..?

Answer 5

No (NH4)2SO4 would dissociate into 3 ions

Answer 6

I dont understand :(

Answer 7

If you haven't looked over the common polyatomic ions, you'll have a very hard time determining how an ionic compound will dissociate.

this list has some common ones and their structures, http://www.chemistry.wustl.edu/~edudev/LabTutorials/PeriodicProperties/Ions/ions.html

So, going back to the example you provided, \((NH_4)_2SO_4\)

the compound dissociates into 3 parts: two ammonium ions \((NH_4^+)\) and one sulfate ion \((SO_4^{2-})\).