CHEM 1203L Kristen Alarcon 04-29-18 Using Freezing Point Depression to Find Molecular Weight Lab Report Abstract- The purpose of this experiment was to determine the freezing of the pure solvent (lauric acid) and the mixture of the lauric acid and benzoic acid to calculate the freezing point depression of the mixture and to lastly calculate the molecular weight of benzoic acid. The mass of the lauric acid was 8.03g and the mass of benzoic acid was 1.025g. After the procedures done in lab the freezing temperature of pure lauric acid was 43.6ºc and the freezing point of benzoic lauric acid mixture to be 38.1º. The moles of benzoic acid solute were then calculated based on the molality and mass of lauric acid solvent, which gave 1.19mol. The experimental molecular weight of benzoic acid was calculated to be 103.95g/mol, which compared to the accepted value of 122g/mol gave a percent of 14.79%. Introduction- In proportion to the number of moles of solute added when a solute is dissolved in a solvent, freezing temperature is lowered. The colligative properties are properties of solutions that are dependent on the ratio of the number of solute particles to the number of solvent molecules in a solution instead of it being compared to the nature of chemical species present. This relationship is shown in the equation below: ΔT = K f xm T is the freezing point depression. Kf is the freezing point depression constant for a solvent. M is the molality of the solution. Benzoic acid and lauric acid in the mixture were measured. From the measurements, the freezing point depression was calculated (molecular weight= mass/moles).
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