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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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michaelg2547 michaelg2547
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11 years ago
0.206 moles of a salt of the general composition M1X1 are dissolved in 545.538 grams of water (Kf = 1.86 K·kg/mol).  Assuming that the salt completely dissociates into individual ions, what is the freezing point of the solution (in °C)?  Assume the pressure to be 1 atm.
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#1
11 years ago
(delta)T = i x k x m

where (delta)T is the change in freezing point, i is the van't Hoff factor, k is the freezing point depression constant, and m is the molality

The MX ionic salt will dissociate to produce 2 ions per mole, so you should multiply by 2. The van't Hoff factor is 2.

molality = 0.206 mol divided by 0.545538 kg water to give a molality of 0.378.

(delta)T = (2)(1.86)(0.378) = 1.4

So the solution would freeze at a temp of NEGATIVE 1.4 degrees Celsius.
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