the solute benzoic acid in the mixture that was measured using a lab balance in

# The solute benzoic acid in the mixture that was

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the solute, benzoic acid, in the mixture that was measured using a lab balance, in grams, divided by the moles of solute calculated above. Purpose : Determine the molar mass of benzoic acid by finding the freezing point of a sample of pure lauric acid and the freezing point depression of known masses of a mixture of benzoic acid and lauric acid. From this information, you can calculate the freezing point depression. The molar mass can then be calculated based on the theoretical foundation discussed in the background section above. Procedure : These steps should be your own steps or flowchart of how to complete the lab. Data : Trial 1 m L = Mass of solvent, lauric acid in the mixture. (g) 8.000 m B = Mass of solute, benzoic acid in the mixture. (g) 1.000 T L = Freezing temperature of pure lauric acid. (°C) 44.0 T (B + L) = Freezing temperature of the benzoic acid-lauric acid mixture. (°C) 41.4
Other observations : When heating the benzoic acid-lauric acid mixture, a white solid on the bottom of the test tube took much longer to melt. It melted much better heating directly over a flame.
Calculations : Freezing point depression of benzoic acid-lauric acid mixture ΔT = T L T (B + L) ΔT = 44.0 °C – 40.4 °C = 3.6 °C Molality of the mixture: Note K f = 3.9 °C•kg/mol for lauric acid as a solvent. f m K ∆Τ = acid lauric kg acid benzoic moles 0.92 0.9231 kg/mol C 3.9 C 6 . 3 = = ° ° = m m Mass, in kilograms, of lauric acid in the mixture m L = acid lauric kg 008000 . 0 g 1000 kg 1 acid lauric 8.000g = Moles of the solute, benzoic acid, in the mixture moles of solute = (molality)(kg solvent) moles of solute = (0.9231 moles benzoic acid/kg lauric acid)(0.008000 kg lauric acid) moles of solute = 0.007385 moles benzoic acid = 0.0074 moles benzoic acid Molar mass of the solute, benzoic acid Molar mass = m B /moles of solute Molar mass = 1.000 g / 0.007385 moles Molar mass = 135.42 = 135.4 g/mol = 140 g/mol