Experiment 3 - Experiment 3 Colligative Properties Freezing...

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Experiment 3: Colligative Properties Freezing Point Depression Lacey Frigaard Lab Partner: Sam Thompson February 12, 2008 Section: 13 Purpose: To explore one of the properties of a solution: freezing point depression. Also, to use this property to determine the molar mass of an unknown substance.
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I. DATA AND CALCULATIONS Table 1: Experimental Data p-dichlorobenzene unknown Table 2: Freezing Point Constant for p-dichlorobenzene Calculations Sample 1 Sample 2 Freezing Point Depression T f = T f ° -- T f = 9.1 ° C—(-2.1 ° C) = 9.2 ° C—(-2.2 ° C) 11.2 ° C 11.4 ° C Moles of solute, p- dichlorobenzene = 0.3 g (1 mol/ 147.0 g) 2.04 x 10 -3 mol 2.04 x 10 -3 mol Molality of solution= Moles of solute Kg of solvent (3.9 g = 3.9 x 10 -3 kg solvent) = 2.04 x 10 -3 mol 3.9 x 10 -3 kg 0.52 m 0.52 m Molal Freezing Point T f = K f m K f = T f /m = 11.2 ° C/ 0.52 m = 11.4 ° C/ 0.52 m 21.5 ° C/m 21.9 ° C/m Percent error Theoretical-Actual *100 Actual = (21.5-20.2)/20.2 *100 = (21.9-20.2)/20.2 *100 6.4 % 8.4 % Table 3: Molar Mass of Unknown Calculations Sample 1 Sample 2 Freezing Point Depression T f = T f ° -- T f = 9.2 ° C – 0.5 ° C = 9.2 ° C – 0.8
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