We weighed 05g of benzoic acid and 40g of lauric acid for the solution and

# We weighed 05g of benzoic acid and 40g of lauric acid

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acid for the solution and followed the same previously listed steps. RAW DATAWe observed the pure lauric acid solvent begin to solidify at about 54.0°C and completely solidify at about 43.4°C. We observed the lauric acid-benzoic acid solution begin to solidify at about 47.1°C and completely solidify at about 44.6°C. The graphs in Appendix A show the temperature vs. time recorded on the LoggerPro for the pure solvent and for the solution. CALCULATIONS/RESULTSWe determined the difference in freezing temperatures, ΔT, between pure lauric acid and lauric acid-benzoic acid solution. ΔT = 54°C – 47.1°C = 6.9°CUsing this and the ΔT = Kf*m formula, we calculated the molality (mol/kg). (Kf= 3.9°C-kg/mol)ΔT/Kf= m 6.9°C/3.9°C-kg/mol = m 1.8 mol/kg = mWe calculated the moles of benzoic acid solute using m and the mass (in kg) of lauric acid solvent.1.8 mol/kg*(0.004 kg lauric acid) = 0.0071 mol benzoic acidThen we calculated our experimental molecular weight of benzoic acid (g/mol) using the mass of benzoic acid solute and the moles of benzoic acid.0.5 g benzoic acid/0.0071 mol = 71g/mol benzoic acidWe found the accepted molecular weight of benzoic acid from its formula C6H5COOH, which is 122.088g/mol benzoic acid.

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• Spring '15