   # Freezing Point Depression Determination SCIENCE LAB EXPERIMENT

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This paper is a full determination for certain chemicals and their boiling points. It lists some already but given the atomic numbers of any material this project includes a conversion and calculation chart to find the freezing point of most any material. GOOD LUCK!

Abstract:

In this lab we determined the freezing point, and Kf, of pure 2,4,dichloralbenzne as well as a 2,4,dichloralbenzne/biphenyl solution. We used this information to determine the molar mass of an unknown (#24) by the 3rd step in the experiment which was a 2,4,dichloralbenzne/unknown solution. All of the above we charted the time temperature for the later calculations.

I. Introduction

A. Background

This experiment shows how one determines the temperature-composition diagram for a two-component system. The procedure will consist of obtaining cooling curves for the pure substances and a number of their mixtures. A cooling curve is constructed by melting a sample, then allowing it to cool, measuring the temperature at regular intervals. When only melt is present, there is a constant cooling rate. As the solid begins to form, the system remains at a constant temperature until the melt is completely converted to solid. The eutectic composition is that at which two solids crystallize out in a ratio equal to that of the melt, and the cooling curve obtained would have the same characteristics as that of a pure substance. The eutectic temperature is the melting point of such a mixture.. The addition of impurity to each of the pure components decreases the freezing point so that two curves are obtained which intersect at the eutectic point.

The freezing point of a solvent depends upon the concentration of the dissolved solute and the nature of the solvent. If the dissolved solute is a nonelectrolyte, then the decrease in the freezing point, DELTA T, is proportional to the molality, m,( moles of solute per kg of solvent) of a dilute solution according to the equation:

DELTA T = Kfm

Where Kf is the

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