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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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obpopnurse obpopnurse
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11 years ago
Find the new boiling point and freezing point of the solvent ethanol in a solution made by dissolving 18 grams of the non-electrolyte fructose C6H12O6 in 200 grams of ethanol, C2H5OH. Normal f.p for ethanol is -114.6 oC and normal b.p. for ethanol is 78.4 oC. Kf for ethanol is 1.99 oC m-1 and Kb is 0.512 oC m-1
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#1
11 years ago
Without actually doing the problem:

First, convert the grams of solute (fructose) into moles.
Next, convert the grams of solvent (ethanol) into kilograms.
Calculate the molality of the solution (molality = moles solute / kilograms solvent)

Change in BP = i (Kb)(molality)
Where:
i = number of dissolved species (1 in this case since it is a nonelectrolyte)

New BP = Original BP + Change in BP

Change in FP = i (Kf)(molality)

New FP = Original FP - Change in FP (Assuming that you are using a positive Kf)
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