A student determines the freezing point of a solution of (0.157 g of an unknown

Question

A student determines the freezing point of a solution of (0.157 g of an unknown solid in 10.24 g of benzene and obtains the following time and temperature data for the solution. Using the data from the table at left, plot 0.0 10.53 Temperature vs. Time on a graph. Use the 0.5 10.04 National Brand Engineering Form #12-188 graph paper specified for this course and read the 8.76 freezing point of the solution from the intersection 8.18 2.0 of the two straight-line plots to the nearest 0.01 degree C. Staple your graph and calculation pages to this 7.04 3.0 prestudy, Cooling time runs from zero to 4.5 3.5 minutes. Freezing time runs from 5 to 8.5 minutes Freezing point of solution K_f for benzene is 5.12 degree C/m the freezing point of pure benzene (Tr degree) is 5.48 degree C. Determine delta T_f and calculate the molecular weight of the unknown solute using Equation 4. Use the masses of solute and solvent given above.

Explanation / Answer

a) please attach the NBE form.

b) Let the molar mass of the solute be 'M g/mole

Now, depression in F.P = Kf*m = 5.12*m ; where 'm = molality of the solution = moles of solute/mass of solvent in kgs = (0.157/M)/0.01024

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