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Unformatted text preview: AP fpd lab v3 Dr. Breinan Chemistry Molar mass by freezing point depression Introduction : Freezing point depression is a classic example of a colligative property. The freezing point of a solution will always be lower than that of the pure solvent. In fact the lowering of the freezing point is proportional to the concentration of solute. Specifically, T f = -k f m, where T f is the freezing point depression, k f is the molal freezing point constant characteristic of the solvent, and m is the molality of the solution. In this lab you will graph a cooling curve (temperature vs. time) for a known amount of pure molecular solvent (stearic acid) and a solution of a known amount of naphthalene (the active ingredient in moth balls) in the solvent. The graph will allow you to determine the freezing point of each, and therefore the freezing point depression. Knowledge of the freezing point depression constant of stearic acid will allow you to determine the molality of the solution and the molar mass of naphthalene. Objectives :- To determine the molar mass of a molecular solute by freezing point depression.- To observe freezing curves for a pure solvent and a solution Materials : stearic acid, naphthalene, large test tube, hot plate, 600 mL and 400 mL beakers, thermometer. CAUTION : * Do not tip the hot water bath. Be careful not to get splashed by the hot water boiling over....
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