Question

3. The molar mass of an unknown solid compound was determined by measuring the freezing poist depression of 1.50 grams of the unknowm in 20.00 grams of Phenol Phenol &Unknown nutes)Temperature 12.5 8.6 1.0 8.2 1.5 6.9 7.8 7.7 .0 75 4.0 7.3 5.0 าอ -3.1 12 60 7.0 3.1 72 9.0 -2.1 7.2 100 7.2 120 7.1 13.0 7.1 15.0 16.0 7.1 On scientific graph paper draw the cooling curves for phenol and the phenol and B. Use the data from the graphs to complete the following table Mass of phenol Mass of unknown Freczing point of mixture (from graph) Freezing point of phenol (from graph) Freezing point depression, AT Freezing point depression constant, K Molality of solution Molar mass of the unknown

The molar mass of an unknown solid compound was determined by measuring the freezing point depression of 1.50 grams of the unknown in 20.00 grams of phenol.

a.) do not need the cooling curve.

b.) please show calculations

Answer 1

∆Tf=Kf×(molality of solution)

Kf=7.4

Here ∆Tf=(7.2-2.2)=5.0

∆Tf= Kf×(mass of solute in gm /molar mass of solute)×(1000/mass of solvent)

5.0 =7.4× (1.5÷m)×(1000÷20)

5.0=7.4{1.5÷m}×5

m=1.5×7.4 =11.10

molar mass of solute=11.10gram