# Mass of benzoic acid Freezing temperature of pure lauric acid

Using Freezing­Point Depression to Find Molecular WeightDATA TABLEMass of lauric acidMass of benzoic acidFreezing temperature of pure lauric acidFreezing point of the benzoic acid­lauric acidmixtureT (the amount of freezing point depression8.540g1.042g43.06C41.089C1.66CDATA ANALYSIS1. Calculate molality (m) in mol/kg using the formula T = Kf m. The Kf value for lauric acid is3.9°C•kg/mol.2. Calculate moles of benzoic acid solute using the molality and the mass (in kg) of lauric acid solvent.3. Calculate the experimental molecular weight (molar mass) of benzoic acid in g/mol.4. Determine the accepted molecular weight (molar mass) of benzoic acid from its formula C6H5COOH.5. Calculate the percent discrepancy between the experimental and accepted values. Using Freezing PointDepression to Find Molecular Weight QUESTIONS6. What is the equation for calculating molality? Why do we use molality rather than molarity as ourconcentration unit for this experiment?7. Use the equation above along with the freezing­point depression equation to derive an expression forcalculating the molar mass of a solute. (Hint: Consider the types of calculations you used in questions 1­3and try to put them together into one mathematical formula.)8. What types of intermolecular forces are present in a molecular solid such as lauric acid? Describe what ishappening with regard to intermolecular forces as a molecular liquid freezes.9. A student spills some of the solvent before the solute was added. What effect does this error have on thecalculated molar mass of the solute? Mathematically justify your answer.10. A different student spills some of the solution before the freezing­point was determined. What effectdoes this error have on the calculated molar mass of the solution? Justify your answer. 11. The freezing point of diet soda is higher than the freezing point of regular soda but lower than 0 °C thefreezing point of pure water.a) Explain why both diet and regular soda freeze at temperatures lower than 0 °C.b) Why does diet soda freeze at a higher temperature that regular soda?12. In order to find the molar mass of an unknown compound a research scientist prepared a solution of0.930 g of unknown in 125 g of a solvent. The pure solvent had a freezing point of 74.2 °C and thesolution had a freezing point of 73.4 °C. Given the solvent’s freezingpoint depression constant K f = 5.50°C/m find the molar mass of the unknown.

Categories Uncategorized