Determination of Molar Mass using freezing point depression Data Analysis/Calcul

Question

Determination of Molar Mass using freezing point depression

Data Analysis/Calculations Use the following questions to assist in determining the molecular mass of the unknown. Be sure to show all calculations. Include the proper significant figures and units! Determine the Delta Tf for the two trials performed. Using the Kf for acetic acid, determine the molality of the solutions for the two trials perform using the equation for freezing point depression in the introduction. Covert the mass of acetic acid from g to kg for each trial. Use the mass of acetic acid in each solution and the molality of the solution calculated in =2 determine the number of mol of unknown present in each solution. Determine the molecular weight of the unknown using the mass weighed out for each trial. Calculate the average molecular weight of the unknown based on the two trials.

Explanation / Answer

Kf for acetic acid= 3.9

delta tf= kf*m

1) delta tf= (16.3+14.7/2)-(13+11/2)= 3.5

2)m=3.5/3.9=.897 m

3)0 .021172 1st trial

0.0206 2nd trial

4)for 1st trial

1.09/mol wt*.021172= .897

mol wt.1= 57.39g

for 2nd trial

1.08/mol wt*.0206=.897

mol wt.2= 58.44

5) avg. mol wt.= 57.39+58.44/2

57.91 g

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