In order to determine the molar mass of an unkown non-electrolyte through FP dep

Question

In order to determine the molar mass of an unkown non-electrolyte through FP depression experiment, the following data was collected:

Mass of test tube = 123.2g, mass of test tube and cyclohexane = 132.11g, mass of test tube, cyclohexane and non-electrolyte = 134.11g, FP of pure cyclohexane = 6.4C, FP of the non-electrolyte in cyclohexane = 2.9C

If Kfp for cyclohexane = -20C/m, calculate the molar mass of the non-electrolyte.

Please show how to do it (decent handwriting and organization is appreciated if written on paper)

Explanation / Answer

weight of cyclohexane = 8.91 g

weight of non-electrolyte = 2 g

delta T = Kf x m

6.4 - 2.9 = -20 x m

m = 0.175 molality

2 g in 8.91 g is 224.46 g in 1000 g

which is 0.175 molality

224.46 is 0.175 moles so 1 mole is 1282 .6 g/mole is the molar mass

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