Using Freezing-Point Depression to Find Molecular Weight
Abstract: In this lab, the purpose was to use the freezing point depression method to determine the molecular weight of aspirin. This was done by determining the freezing of t-butanol and that of a t-butanol and aspirin solution; then finding the molality of the solution, and moles of aspirin. In the results of the experiment, the molar mass was found to be 192.2 g/mol, which differed from the established value of 180.2 g/mol by 6.7% error.
Freezing point depression defined as a vertical medium in reference to boiling point elevation. The general definition is the effect of lowering the freezing point of a substance due to an increased amount of solute added
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This decrease in vapor pressure and increase in solute present caused the freezing point to became lower when mixed thin the solution. The purpose of this lab was to determine the molecular mass of aspirin by measuring the freezing point depression. This was done by reacting t-butanol with aspirin as a solute. A pure solvent of t-butanol’s freezing point was first determined by melting and freezing it and then the solute was added and the freezing point dropped. This difference was the freezing point depression of the solute. From this freezing point change, the molecular mass of the solute was calculated. The first trial with 0.200 g of the solute produced a molar mass of 748 g/mol and the second trial with 0.195 g of the solute produced a molar mass of 192.2 g/mol. The molar mass of the first trial was way off from the accepted value, while the molar mass of the second trial was quite close to the accepted value. These results were confirmed when a percent error of 315% in for the first trial and 6.7% in the second trial. Errors that contributed to the percent error could include impurities in the aspirin and