lab final part 4.docx - Part Four Freezing point Depression...

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Part Four: Freezing point Depression Introduction: Freezing point depression is the lowering of the freezing point of a solvent by adding a solute. It is colligative property which means that the amount of solute particles, and not the specific solute present, determines the degree to which the freezing point is depressed. The mathematical expression for the freezing point depression is given in the equation ∆T = ik f m where i is the van’t Hoff factor and k f is the freezing point depression constant for a solvent and m is the molality. Molality is found by plugging into the formula (moles of solute/ kg of solvent) the freezing point depression for water is 1.86 C/m. The Van’t Hoff factor is the number of particles in a given solution. It is important to keep in mind that since ionic compounds form several aqueous ions, the theoretical van’t Hoff factors are greater than one. For covalent compounds, like sugar, that dissolves in water, the theoretical van’t Hoff factor is 1 because they do not break up in a solution. Remember that freezing point is a colligative property and so the number of particles in solution, and not the specific chemical present, effects the freezing point depression. In this part of the lab we will freeze 5g of a solution three times, let it soak in a salt ice bath, while stirring continuously, then use the micro lab to measure the freezing point (after super cooling) to determine if the recipe was stolen or not. We use salt a bath instead of a regular
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