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Chem. II Lab- Freezing Point Determination and Freezing Point Depression of a Solvent

# Chem. II Lab- Freezing Point Determination and Freezing Point Depression of a Solvent

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Lab Report Devon Corcoran Chem. II Lab Dr. Ward Freezing Point Determination and Freezing Point Depression of a Solvent Introduction As solids are heated, their temperatures rise until they meet their melting point. When the melting point is reached, the temperature will remain constant until all of the solid is melted. The temperature will then continue to rise until the liquid reaches its boiling point. When the boiling point is reached, the same phenomena occurs. The temperature remains constant until all the liquid is vaporized, and then continues to rise. The melting point and the freezing point are the same, and can be determined by graphing the rise in temperature of the solid as it melts and continues to rise after melting and continuing to graph as the liquid refreezes. This graph demonstrates how the temperature levels off at points of phase change and then continues to rise: Boiling Point of Water 0 20 40 60 80 100 120 140 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 Time (Minutes) Temperature When a solute is added to a solvent, it’s freezing point is lowered. The freezing point depression for a one molal is called the freezing point constant ( K f ). Using the K f and the Δ T , we can find the molar mass of the added solute by means of the equations m T K f = and solvent solute kg moles m = . The equation for molality ( m ), can be rearranged to read ( 29 ( 29 solute solvent solute M kg g m = , and thus becomes very useful in identifying the solute. The objective of these experiments is to learn to determine the freezing point of a liquid and to determine the freezing point after a solute is added and to calculate the molar mass of that solute.

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Experimental A 600 mL beaker ¾ full of water was placed on a ring stand and heated to almost boiling. Two
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Chem. II Lab- Freezing Point Determination and Freezing Point Depression of a Solvent

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