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postlab7 - L aura Lanier Lab L2 Experiment 7 D iscuss ion...

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Laura Lanier Lab L2 – Experiment 7 10/22/09 Discussion /Conclusion Throughout the whole of the first part of the experiment (finding the unknown compound), the freezing point was found by averaging the temperatures recorded after the region of supercooling. Through this experiment, the freezing point of distilled water was found to be 1.48 ˚ C; although this is obviously not the freezing point of pure water, the percent error cannot be calculated because division by zero is an undefined number. This deviation was most likely caused by impurities in the water. The freezing point in the first trial was found to be -1.38 ˚ C and was found to be -0.51 ˚ C in the second trial. The observed measurements of the freezing points of the solution including the unknown were very different in each separate trial; this deviation can be attributed to the difference in the amount of water and the amount of unknown that were used in each trial. These observed freezing points caused a 2.86 ˚ C and 1.99 ˚ C change in the freezing point of water, respectively. Using this depression in the freezing point of water and its equation, the molality of the solutions was calculated to be 1.54 mol/kg and 1.07 mol/kg, respectively. To find the number of moles of unknown in each sample, the molality of the solution is multiplied by the kg of water, yielding 0.0152 moles in the first trial and 0.0103 moles in the second. Finally, to find the experimental molar weight of the unknown, the mass of the unknown, 0.510 g in the trial 1 and 0.551 in trial 2, is divided by the number of moles with the final result being 33.65 g/mol and 53.38 g/mol, respectively, yielding an
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