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CHM151LL: DETERMINATIONOFMOLARMASSBYFREEZING-POINTDEPRESSION| 1Determination of Molar Mass by Freezing-Point DepressionOBJECTIVES:Gain familiarity with colligative properties of nonelectrolyte solutionsFind the molar mass of a solute by the method of freezing-point depressionEvaluate the accuracy of the method by comparison to a molar mass calculated from a molecular formula.DISCUSSION:When a solution forms, the freezing point of the solution is lower than the freezing point of thepure solvent. The magnitude of this freezing-point depression (∆Tf) depends only on the numberratio of solvent and solute molecules (or ions) in the solution, not on their chemical identity. Thismakes ∆Tfone of the colligative propertiesof solutions.If we use molalconcentration cmdefined so that 1 m=1 mol solute1 kg solventæèçöø÷, then the freezing-pointdepression follows a simple direct proportionality relationship:∆Tf= Kf cm(1)where the proportionality constant, Kf, is called the molal freezing-point depression constant.Lauric acid (the solvent in this experiment) has a reported Kf= 3.9 °C·kg/mol = 3.9 °C/m.In this experiment, you will determine the freezing point of the pure solvent, CH3(CH2)10COOH(lauric acid). You will then find the freezing point of a lauric acid solution that contains ameasured mass of solute C6H5COOH (benzoic acid) and determine the freezing-point depression.Using the experimental ∆Tfvalue and the reported Kfvalue in equation (1) will enable you tofind the amount (in moles) of benzoic acid in your solution. This value, along with the knownmass of benzoic acid, leads to the molar mass determination.PROCEDURE:Part I–Freezing point of pure lauric acid1.Set up two water baths (one above 70°C and one at room temperature) using 400-mL beakersfilled to about the 300-mL level. Obtain a sample of pure lauric acid in a sealed test tube.