Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: hmrobinson09 on February 24, 2009, 08:16:37 PM
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Can someone help me with this?
A solution of 2.24 x 10-1g of an organic compound of unknown molecular weight in 1.664g of camphor gave a freezing point of 176.44 Celsius. The freezing point of camphor is 179.80 Celsius, and the freezing point depression constant Kf 39.7 Celsius/m. Calculate the molecular weight of the unknown.
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What is formula for calculation of freezing point depression?
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Here is a formula which can be used to calculate the Molecular Weight of the solute:
ΔTf = (kfxW2x1000)/(M2xW1)
where ΔTf = Depression of freezing point
kf = Molal Depression Constant(Cryoscopic constant)
W2 = Weight of the solute
W1 = Weight of the solvent &
M2 = Molecular Mass of the solute.
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ΔTf = (kfxW2x1000)/(M2xW1)
While it is not wrong, it may be confusing, as it makes several conversions in one step, instead of concentrating on the general concept:
ΔTf = kf m
where m is molality.