Lab 1: Colligative Properties & Osmotic Pressure

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Ankur SindhuSep 20, 2011
CHEM 182-DL1
Prof.: Dr. Nidhal Marashi

Lab 1: Colligative Properties & Osmotic Pressure

Purpose: The purpose of this laboratory was to gain an understanding of the differences between the freezing points of pure solvent to that of a solvent in a solution with a nonvolatile solute, and to compare the two.

Secondly, osmosis was to be observed to gain a proper understanding of how the principal of dialysis functions.

Procedure:

1. Make a water bath assembly by doing the following:
a. Half-fill the 100-mL beaker with cool tap water.
b. Place crushed ice in the beaker so the water level is just below the top of the a. beaker. The water level should not be higher than the length of the test tube. b. Sprinkle a little salt into the ice water. Mix well. 1. Half-fill the test tube with distilled water. Set the tube into the 24-well plate. (The well plate will function as a test tube holder.) 2. Insert the thermometer into the test tube and take readings every 30 seconds until the readings remain constant, then record the temperature of the distilled water. 3. Place the test tube in the beaker‘s ice water bath and set your stopwatch at zero. 4. Carefully stir the water in the test tube with the thermometer and record the temperature of the water at 30-second intervals. You should see the temperature of the water rapidly decrease to from -1C to -3C then rise to 0C. At that time the readings should remain constant before again decreasing. This is super cooling. 5. Caution: Do NOT let the water in the test tube freeze completely or the thermometer may break. 6. Once five consecutive readings have been made at a constant temperature, remove the test tube from the bath and empty it into a sink.

7. Refill half of the test tube with room temperature distilled water (at least 10C) and add 1/8 teaspoon of salt to the distilled water in the test tube. Mix well until dissolved.
8. Either prepare a fresh water bath or add more ice and a little salt to the existing water bath. 9. Repeat Steps 2 - 5 above using the saltwater solution prepared in Step 7 above. You may not observe super cooling this time. 10. Pour the water from the test tube and from the water bath down the drain. Clean up your equipment and replace it in the LabPaq.

Two graphs were then made for each of the two experiments. The y-axis of the graph was the temperature recordings and the y-axis was the time in 30-second intervals. Two straight lines were then drawn on each of the graphs from the initial temperature to coldest temperature observed and straight across the 5 constant temperature recordings. The point at which these lines intersected was recorded as the freezing points of the pure solvent and the solution. In the second part of this laboratory a glass bowl was filled with distilled water and dialysis tubing was placed in it for 30 minutes. After 30 minutes, the dialysis tubing was taken out of the water and the water was discarded. At one end of the dialysis tubing a small rubber band was wrapped around it to ensure a tight seal. The dialysis tubing was then was then filled to ⅓ capacity with clear Karo syrup, with the assistance of a small funnel. The open end of the dialysis tubing was then closed tightly using a small rubber band, as was previously done with the other end. The dialysis tubing was then placed in a bowl and the bowl was filled up with distilled water. An effort was made to ensure that the dialysis tubing was completely submerged in the distilled water.

Observations of the dialysis tubing were made every hour for a total of 5 hours and recorded. Following the dialysis tube observation, a raw egg placed in a pint jar. Observations of the egg were then made and recorded. White vinegar was then poured over the egg until it was completely submerged. The jar was then sealed and the egg was observed after 12 and 24 hours had...
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