Computer 4 Advanced Chemistry with Vernier 4 - 1Using Freezing-Point Depression to Find Molecular Weight When a solute is dissolved in a solvent, the freezing temperature is lowered in proportion to the number of moles of solute added. This property, known as freezing-point depression, is a colligative property; that is, it depends on the ratio of solute and solvent particles, not on the nature of the substance itself. The equation that shows this relationship is t= Kfwheretis the freezing point depression, Kfis the freezing point depression constant for a particular solvent (3.9°C•kg/mol for lauric acid in this experiment1), and mis the molality of the solution (in mol solute/kg solvent). OBJECTIVES In this experiment, you will Determine the freezing temperature of the pure solvent, lauric acid. Determine the freezing temperature of a mixture of lauric acid and benzoic acid. Calculate the freezing point depression of the mixture. Calculate the molecular weight of benzoic acid. mFigure 1 MATERIALS Vernier computer interface lauric acid-benzoic acid mixture computer hot water bath Temperature Probe two 18 150 mm test tubes ring stand utility clamp 400 mL beaker paper towel or tissue lauric acid, CH3(CH2)10COOH 1 “The Computer-Based Laboratory,” Journal of Chemical Education: Software, 1988, Vol.1A, No. 2, p. 73.
Computer 4 4 - 2Advanced Chemistry with VernierPROCEDURE 1. Obtain and wear goggles.