AP LAB - Freezing Point Depression - LAB Using Freezing-Point Depression to Find Molecular Weight When a solute is dissolved in a solvent the freezing

AP LAB - Freezing Point Depression - LAB Using...

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LAB - Using 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: ΔT = K f • m where Δ T is the freezing point depression, K f is the freezing point depression constant for a particular solvent (3.9°C-kg/mol for lauric acid in this experiment), and m is the molality of the solution (in mol solute/kg solvent). Purpose : In this experiment, you will first find the freezing temperature of the pure solvent, lauric acid, CH 3 (CH 2 ) 10 COOH. You will then add a known mass of benzoic acid solute, C 6 H 5 COOH, to a known mass of lauric acid, and determine the lowering of the freezing temperature of the solution. By measuring the freezing point depression, ΔT, and the mass of benzoic acid, you can use the formula above to find the molecular weight of the benzoic acid solute, in g/mol. Equipment : Data collection device, Stainless Steel Temperature Probe, 18x150 test tube, 400 mL beaker, hot plate Materials : lauric acid, benzoic acid, water Procedure : 1) Prepare the apparatus for data collection by making sure the data collection device (laptop, calculator, etc.) and the temperature probe are linked and working properly.
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  • Fall '16
  • Algebra, Freezing-point depression, Lauric acid

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