need help with freezing point depression problem

[zaci1]

Hi to all =]

 

 

I have been trying to solve the following problem:

 

 

For propanoic acid:

 

delta T = delta (melting temperature) = 0.0193 K

 

m = molality = 0.01 mol/kg

 

Kk = cryoscopic constant = 1.86 K kg / mol

 

density = 1.00 g/ml

 

 

I need to calculate the dissociation constant.

 

 

(the correct answer is 1.42 * 10^-5 mol/l)

 

[form: Izbrana poglavja iz biokemije 1; A. Bavec et al.]

 

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So the way i tried to solve it is write this equation:

 

CH3-CH2-COOH <-> CH3-CH2-COO^- + H^+

 

 

I also know this equation:

 

delta T = Kk * m

 

or:

 

delta T = Kk * m * i > where i is the van't Hoff factor

 

 

1. I tried to calculate m by inserting the delta T and Kk values into the first equation.

 

2. I tried to calculate i by inserting all known values into the second equation.

 

I know that the delta T will be greater when there are more particles dissolved, so the equation for the dissociation will favor the right part of the equation (with the free protons).

 

But really, i'm kinda clueless what to do. I really hope someone will be able to help me solve this problem or point me to the right resources so i can solve this or similar problems... Any help greatly appreciated =]