CHEM 2 lab 4

CHEM 2 lab 4 - Bobby Bardin II 10/10/07 Chemistry...

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Bobby Bardin II 10/10/07 Chemistry experiment 4 Colligative properties Laboratory Purpose: The purpose of this lab was to determine the molar mass of an unknown sample by studying the freezing point depression of lauric-acid solution with a known concentration of the sample by using the formula ∆T = K f m where K f is the freezing point constant of the solvent and m is the molality. Procedure: Refer to handout for Exp. # 4. Data and observations: Refer to the attached charts and graphs for the data. From looking at these graphs, it is apparent that the freezing point of lauric acid is 42.6 o C. In part B, after adding the unknown sample, the freezing point appears to drop to 40.3 o C. Results and calculations: ∆T = K f m . ∆T = the change in temperature, so ∆T = 42.6 – 40.3 = 2.3 o C K f is the freezing point constant, which, for lauric-acid, is 3.9 o C / m m is the molality of the solution, which can be calculated by m = ∆T / K f = 2.3 / 3.9 = .590 Since the molality is .590, and molality is the mol solute / kg solvent:
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CHEM 2 lab 4 - Bobby Bardin II 10/10/07 Chemistry...

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