Freezing Point Depression Determination SCIENCE LAB EXPERIMENT

Topics: Melting point, Freezing-point depression, Thermodynamics Pages: 14 (2033 words) Published: May 17, 2004
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!


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:


Where Kf is the molar freezing-point depression constant unique for each solvent.

Super cooling often occurs in this system. The cooling curve will show a momentary dip below the mixture's freezing point, and then will revert back up to the freezing point. This is usually helpful in determining the freezing point, provided the super cooling is not too pronounced. Excess super cooling may be avoided by seeding the melt with very small crystals of the solid.

B. Purpose of the investigation.

This experiment as stated above shows how one determines the temperature-composition diagram for a two-component system. The freezing point of a solvent depends upon the concentration of the dissolved solute and the nature of the solvent. If you follow the procedure stated below you will learn about freezing point depression as well as understand why we use certain solutions for different applications like antifreeze and break fluid, and it's not just limited to cars.

II. Procedures

First thing you will need to do is Preview the procedure and understand what is going on so you know all the precautions, how to obtain chemicals execute the experiment clean up and make the calculations. In the first step you will need to gather all the supplies you need.

Needed interments and chemicals(Gather the following ):

1. A cooled down hot plate

2. A support ring

3. 600 ml beaker filled of tap water and 2 or 3 boiling chips

4. 16x150-mm test tube

5. A bent wire or glass rod for stirring

6. 2 clamps

7. thermometer

8. cork to hold thermometer

9. chemicals stated below as needed

B. Outline of procedure

Steps to execute procedure


2. Gather supplies

3. Clean all glassware and thermometer and wipe clean with chem. wipes

4. Set up apparatus like to the right

5. Measure the test tube to the nearest .01 gram

6. Add 5 to 6 grams of 2,4,dichloralbenzne

7. than re-measure the test tube

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