Gen Chem Question

[gwest]

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Which of the following concentration is temperature dependent?
................the answer is Molarity

fellow SDNers does any1 have a quick explanation for this? thanks for the help

 

[Ex_EE]

Molarity is moles of solute / volume of solution. Volume changes with temperature because density varies with temperature.

 

[dddsmack]

true

 

[gwest]

thanks for the easy explanation! i have another...

If the following solutes are used to prepare 0.1 molal solutions in water, which solute will give the solution with the lowest freezing point?

1. CaCl2
2. NaCl
3. C2 H4 O2
4. C2 H6 O
5. C6 H12 O6

so my logic was: well 2 find which solute that has the lowest freezing point, which 1 has the highest mm. Glucose I though. But the answer is 1, Calcium Chloride. y?????

 

[celeron_266]

freezing point depression is a collagative property, meaning that it depends solely on the amount of dissolved stuff is in the solution, the more stuff, the lower the freezing point

assuming 1kg of 0.1m calcium chloride, when dissociated, gives 0.1mol calcium and 0.2mol chloride, sodium chloride gives only 0.1mol sodium and 0.1mol chloride, the other three choices either does not dissociate well or does not dissociate at all

since the calcium chloride have the most dissolved substances (total 0.3mol in a 1kg solution), its freezing point is the lowest