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Colligative Properties Essay

Abstract:

Several experiments were performed to observe the colligative properties. This includes the freezing point depression, and osmotic pressure. Two ice baths were made, one with pure water, the other with salt water. The lowest temperature was then record for each bath and compared. The salt water had a lower freezing point than the pure water by 2 degrees which supports the hypothesis that solutions have a lower freezing point than pure water. The second property observed was osmosis pressure. This experiment used a 6 inch piece of dialysis tubing that was filled 2/3 full with light Karo syrup and tied off. Then it was completely submerged in a large glass bowl of room temperature distilled water. The dialysis tubing acts as a semi-permeable barrier and water passed through to inside the tube and over the next several hours, this act caused the tube to swell. Osmosis is where water moves from an area of high concentration to low concentration, therefore causing the tube to swell.

The last experiment involved placing an egg in a jar of vinegar. After 24 hours, the shell of the egg completely disintegrated. Then the jar was rinsed and refilled with Karo syrup where the egg was submerged for 48 hours. This allows osmosis to take place where the water inside the egg leaves and moves outside where thereis a lower concentration of water. Thus, making the mass of the egg smaller. This series of experiments takes a closer look at the colligative properties, specifically the freezing point depression and the osmotic pressure. Colligative properties is where the concentration of solute particles in a solution is what is important and not necessarily the chemical identity of the solute.

The first part of this experiment focuses on the freezing point depression. The freezing point depression is based on the idea that a solution freezes at a lower temperature than the freezing point of pure water. Finding the freezing point of a substance allows the molar mass of a substance to be calculated. The second part of this experiment observes the colligative property of osmotic pressure. Osmosis is based on the idea that water will go from an area of high concentration to an area of low concentration. With this information, we can determine the identity of a substance.

Purpose:

Determine the freezing point of water
Find the freezing point of a solution
Observe osmotic pressure.
Procedures

First, an ice water bath was prepared filling a 100ml beaker halfway with cool tap water and adding a pinch of salt and some crushed ice. Then, the temperature was recorded with a thermometer placed in a test tube until a consistent temperature was observed and recorded. Then the test tube was placed in the ice bath. Then, the thermometer was stirred inside the test tube continuously while the temperature was recorded every 30 seconds until the temperature was consistent again for 5 consecutive readings. The same procedure was repeated a second time, though this time with some salt in the test tube. Another ice bath was prepared in a 100ml beaker filling it halfway with distilled water and a pinch of salt. An 1/8 teaspoon of iodized salt with distilled water filled up another test tube. The initial temperature was recorded until a consistent temperature was observed.

Then, the test tube was placed in the ice bath, while the thermometer was stirred inside the test tube recording the temperature at 30 second intervals until a consistent temperature was observed. Initially, the temperature of the salt water mixture did not decrease substantially so another 1/8 teaspoon of iodized salt was added. The second property we observed was osmotic pressure. A 6 inch piece of dialysis tubing was placed in room temperature water for 30 minutes to soak. One end of the tubing was sealed off by tying the end in a knot. Then the tubing was filled 2/3 full with light Karo syrup and the other end was tied shut leaving some space to expand.

Then the tubing was placed in distilled water over a period of several hours and recorded and observed. The last experiment also observed osmosis. An ordinary large white egg was placed in a quart size mason jar filled half way with white vinegar and the lid screwed shut. Then, it soaked for 24 hours and was rinsed off with distilled water. The jar was rinsed out as well and refilled half the mason jar with light Karo syrup. The egg was placed back in the jar with the Karo syrup with the lid shutThe egg’s changes were observed and recorded over several days. Temperatures for the Ice Bath experiment:

Answers to Lab Questions
Part 1

B. The freezing point of the pure water is -2 degrees while the freezing point of the salt solution is -5 degrees. C. The salt solution has a lower freezing point because water is the only thing that freezes, so the salt is left behind. Molecules must enter and leave the solid phase at the same rate. This occurs at a lower temperature for the solution because of the vapor pressure. D. Some practical applications of cognitive properties include salting the roads in the winter.

The salt lowers the freezing point of snow/ice, so it takes a lower temperature for roads to freeze over. Antifreeze in a car can be used to lower the freezing temperature and also it can be used to raise the boiling point so cars will not overheat in the summer months. Freeze drying is an example of vapor pressure lowering. The vapor pressure of the surrounding air is lowered, and it causes the surrounding air to take heat from the substance which then freezes which preserves perishable materials.

Part 2
A. The dialysis bag is comparable to a cell membrane. It allows water and small particles through, while stopping large particles from passing through. It is different from a cell membrane because a cell membrane uses many processes to transport materials across the membrane including active transport and passive transport, while the dialysis tubing simply uses diffusion. B. The Karo syrup is hypertonic to the egg. Th concentration is higher outside the egg than inside, so the water moves outside of the egg.

C. N=MRT
8.34 mmHg osmotic pressure
23.6 degrees Celcius
0.5 L of solution containing 0.302 grams of antibiotic
8.34 mmHg * 1atm/760 mmHG = 0.01097 atm
0.01097 atm = M (0.0821) (23.6 +273 = 296.6 K)
M = 0.01097atm/(0.0821*296.6K)
M = 0.01097atm/24.35086
M = 4.505X 10-4 moles of antibiotic
Moles = molarity X Volume
(4.505 X 10-4 moles/L) X (0.5 L) = 2.2525 X 10-4 moles
0.302g/2.2525 X 10-4 moles = 1340g/mole

Results/Analysis:

The freezing point of the solution was -5 degrees, while the freezing point of the pure water was -3 degrees, This is a 2 degrees difference in the freezing points. This supports the hypothesis that solutions have lower freezing points. The freezing point depression is a colligative property used to calculate the molar mass of a substance. However, It was not possible to calculate the molar mass of our substance because with a home lab kit there was no weighing involved. We were still able to record and determine the freezing point of both distilled water as well as salt water. Given more tools to properly execute the experiment, we would have come out with more accurate result and complete results.

For the Karo syrup experiment, after several hours of observing the Karo syrup in the dialysis tubing. The tubing swelled up some, however too much Karo syrup was placed in the bag and there was not much room left to swell. The egg was placed in vinegar and the shell completely disappeared after about 24 hours. Then, when placed in Karo syrup for a 48 hours, the egg’s mass appeared smaller. The water inside the egg moved out into the surrounding solution, therefore making the egg’s mass smaller. Conclusion:

The freezing point depression was observed for pure water as well as salt water. The salt water ice bath had a lower freezing point which supports our original hypothesis. Osmotic pressure was observed both in the egg experiment and in the dialysis tubing experiment. The egg lost its water content and the dialysis tubing swelled up. Even though the basic colligative properties were demonstrated with these experiments, more accurate results would have been obtained in a more controlled environment. Knowing the weight of the salt would have been helpful in determining the molecular mass.


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