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