Destroyer #18 lowest freezing point

[Xtian]

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Hi all,

I'm prepping for my DAT and quickly discovering all I've seemed to forgotten pertaining to G chem.

#18 Destroyer: Which solution has the lowest freezing point?
a. 0.2M KCl
b. 1.2M C6H12O6
c. 1.4M NA2SO4
d. 2.4M C2H5OH
e. 1.8M NaNO3

Answer is C. Please help.

Thanks,

Xtian

 

[osimsDDS]

you have to look at the vont-hoff factor for this problem...

Na2SO4 can dissociate into 3 components while the others dissociate into less...then multiply by the Molarity...im not gonna do the math but im guessing since Na2SO4 can dissociate into 3 the answer is prob that one...

 

[topdent1]

Hi all,

I'm prepping for my DAT and quickly discovering all I've seemed to forgotten pertaining to G chem.

#18 Destroyer: Which solution has the lowest freezing point?
a. 0.2M KCl
b. 1.2M C6H12O6
c. 1.4M NA2SO4
d. 2.4M C2H5OH
e. 1.8M NaNO3

Answer is C. Please help.

Thanks,

Xtian

The solution with the lowest freezing point relates to a colligiative property called freezing point depression. It depends on the number of ions in solution. In order to figure this out, you have to multiply the number of ions that result from each compound by the molarity given to get the 'effective concentration' For example, c. Na2SO4 dissociates into 2Na+ and SO42-. Therefore three ions are produced right? Multiply this by 1.4 and you will get the highest effective concentration which means it will have the lowest freezing point.

 

[PooyaH]

As everyone else said: find the number of ions and multiply it by the concentration given, whichever gives the highest number would have the lowest freezing point.
But remember, sometimes they ask you which one has the highest freezing point!? Then, you still do the same thing but pick the lowest number!

 

[Xtian]

Ya'll ROCK!

Thanks,

Xtian

 

[klutzy1987]

The formula for freezing pont depression is DeltaT=Kf*m*i.

i= the ions in solution, therefore the more ions, the more the freezing point is depressed.