Question

Calculate the molar mass of each Compound :

Gycerol

NaCl

CaCl

This is for the lab experiment on Molar Mass and freezing point,
and these are the results l got.

Solution. Freezing point
in degreesC

H2O.
0

Gycerol.
-3.5

NaCl.
-5.7

CaCl.
-4.0

How do these molar masses compare to the theoretical. Calculate the
percent error. glycerol I have 0.04470, and 0.0383 for NaCl and
0.01792 for CaCl. I know there is a constant l am supposed to use
to get the theoretical molar mass, but l am stuck.

Answer #1

Depression in freezing point and molar mass calculation

dTf = -iKfm

Kf = 1.86 oC/m

For glycerol solution in water

molality = dTf/iKf

= 3.5/1 x 1.86

= 1.882 m

molality = grams of solute/molar mass x kg of solvent

[pl. note mass of solvent is not given here]

then,

molar mass = grams of solute/molality x kg of solvent

= 0.04470/1.882 x kg of solvent

= molar mass (g/mol)

Similarly we can do the calculation for the rest

For NaCl take i = 2

For CaCl2 taken i = 3

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