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. . 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. . 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 ? 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 passed and the observations were recorded.
The egg was then removed after 24 hours and placed in another pint jar and submerged in Karo syrup. The lid was then placed on the jar and an observation was made and recorded. Observations of the egg were then made after 12 hours and 24 hours had passed and the observations were recorded. After 24 hours had passed, the egg was removed from the syrup and rinsed with tap water and observations were made and recorded. Data Tables and Graphs: Temperature of Distilled Pure Water Time | Temperature (C)| 0| 1| 30| -1| 60| -1| 90| -1| 120| -1| 150| -1| Temperature of Salt Water Solution
Time (s) | Temperature (C)| 0| 0| 30| 8| 60| 5| 90| 2| 120| 0| 150| 0| Part 2. Osmosis Observations of Syrup Filled Dialysis Tubing 0 Hours | Tubing limp and filled ? of way with syrup| 1 Hours| Tubing appears to have accumulated more liquid inside. Still a little limp| 2 Hours| Tubing is now half filled with liquid and is more stiff| 3 Hours| Tubing is ? of the way filled with liquid and is very stiff| 4 Hours| Tubing is almost completely full of liquid and very stiff| 5 Hours| Rubber band at one of the end of the tubing has come off| Observations of Raw Egg
Time| Raw Egg| Raw Egg in Vinegar| Raw Egg in Syrup| Raw Egg Rinsed off with tap water| 0 Hours| Oval shaped, white, opaque and hard shelled| Oval shaped, white, opaque, bubbles rising out of vinegar| Oval shaped, large, translucent yellow, no shell| Still soft and small and is pale yellow in colour| 6 Hours| | Slightly yellow, bubbles in vinegar| Translucent yellow, large size, no shell| | 12 Hours| | Yellow bubbles in vinegar, shell thinning | Slightly smaller in size, translucent yellow, no shell| | 24 Hours| | Translucent yellow, larger in size, no shell| Noticeably smaller in size, still yellow| |
Observations: In the second part of this laboratory, osmosis caused the syrup in the dialysis bag to enter the water and water to enter the dialysis bag until they were at equilibrium. I do not think that equilibrium was reached because the osmotic pressure caused the rubber band to come off the end of the dialysis tubing. With the raw egg experiments, I believe that a certain element in the eggshell must have bonded with another element in vinegar and left in the form of the bubbles. This is what probably caused the shell to disappear.
The vinegar was also hypotonic to the egg clearly making the egg larger. The syrup solution was hypertonic to the egg making the egg smaller. Questions A. To what biological structure is the dialysis bag comparable? How is it similar? How is it different? The dialysis bag is similar to the cell wall of a cell. It is similar in that it allows water in and out in order to achieve equilibrium through osmosis. It is different because a cell also allows things in through active and passive transport. The dialysis tubing only allows things in and out based on the size of the permeations in the dialysis tubing. B.
In biological systems if a cell is placed into a salt solution in which the salt concentration in the solution is lower than in the cell, the solution is said to be hypotonic. Water will move from the solution into the cell, causing lysis of the cell. In other words, the cell will expand to the point where it bursts. On the other hand, if a cell is placed into a salt solution in which the salt concentration in the solution is higher than in the cell, the solution is said to be hypertonic. In this case, water will move from the cell into the solution, causing cellular death through crenation or cellular shrinkage.
In your experiment is the Karo® hypertonic or hypotonic to the egg? The Karo is hypertonic to the egg. This is clear because the egg shrunk in size. Problem for Lab Report: At 23. 6C, 0. 500 L of a solution containing 0. 302 grams of an antibiotic has an osmotic pressure of 8. 34 mmHg. What is its molecular mass? 8. 34 mmHg x 1 atm/760 mmHg =0. 01097 atm 0. 01097 atm = M(0. 0821) (273 + 23. 6) 0. 01097 atm = M(0. 0821) ( 296. 6) M= 0. 01097/ ( 0. 0821)(296. 6) = 4. 5 x 10^-4 Molarity = moles/L 4. 5 x 10^-4 = moles/0. 5 = 2. 25 x 10^-4 moles 0. 302 grams/2. 25 x 10^-4 moles = 1342. 2 grams/moles Conclusion:
In the fist part of this lab, the results surprised me. I had thought prior to completing the experiment that the salt-water solution would have lower freezing point than the distilled water. It was also surprising that the rubber band came undone from the end of the dialysis tubing. The osmotic pressure must have been extremely high. I was also fascinated to see the eggshell dissolve in the vinegar. I did not expect that to happen, even though the lab manual said it would. Vinegar contains acetic acid, which breaks apart the solid calcium carbonate crystals that make up the eggshell into their calcium and carbonate parts.
The calcium ions float free, while the carbonate goes to make carbon dioxide. The bubbles that I observed were actually carbon dioxide floating away. I had expected the egg to enlarge when placed in the vinegar and I had expected it to shrink when I placed it into the syrup. I thought that I had a decent understanding of what would be hypotonic and what would be hypertonic, until the end of the experiment. I thought that when I rinsed the egg off, that it would increase in size again. Frankly, it may have if I submerged it in the tap water for a prolonged period of time.