Freezing Point Depression

Freezing Point Depression - Freezing Point Depression of...

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Freezing Point Depression of Water Group Participants: Jason Christian , Connor Dennis, Josh Istas Section Number: 416 Meeting Time: 7:30-10:20 November 16, 2006 TA: Amanda Reeves Introduction All pure substances have a set freezing temperature. When another substance is added to the pure substance, the freezing temperature lowers. For example, pure water freezes at 0°C. When another liquid is added to the pure water, the freezing temperature of the solution is below 0°C. The reason for this is by adding impurities, the entropy of the solution increases. As entropy increases, stability of the solution increases. The change in temperature of a pure solution to the lower temperature of an impure solution is called the freezing point depression. This is known as a colligative property of a solution. A colligative property of a solution is a property that changes according to the type and amount of solute in the solution. Colligative properties of a solution include: freezing point depression, boiling point elevation, and osmotic pressure. The freezing point depression of a solution is related to molality by the equation: ° ΔT f = K f m where ΔT f is the freezing point depression ΔT f = T f (H 2 O) – T f (Solution) K f is a constant for the solvent ~ for H 2 O, K f = 1.858 m C ° m is molality = Solvent of Kilograms Solute of Moles Molecular Weight = Compound of Moles Compound of Grams Through the experiment, the molecular weight of the compound added to water was calculated. By using experimental values of ΔT f , the molecular weight of an unknown solution was experimentally found.
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Experimental Freezing Point of H 2 O (Part One) First, about 30 mL of deionized water was massed and poured into a 50 mL Erlenmeyer flask. Then, an “ice bath” was made using dry ice (without water) in a 600 mL beaker. The Erlenmeyer flask was placed into the dry ice bath.
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This note was uploaded on 04/07/2008 for the course CHEM 185 taught by Professor Berrie during the Spring '08 term at Kansas.

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Freezing Point Depression - Freezing Point Depression of...

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