Colligative Properties Osmotic Pressure free essay sample

Important terms to study from this lab assignment are colligative properties, membrane permeability and osmotic pressure. First, colligative properties are â€Å"those of a solution that depend solely on the number of solute particles present, not the identity of those solute particles. These properties include: vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure† (p. 17 lab manual). In this experiment freezing point depression is illustrated by comparing the freezing point of distilled water to the freezing point of distilled water mixed with a non volatile solute, salt. Another important term taken from this lab experiment is membrane permeability, which is the ability of the membrane to pass a solution through it. Membrane permeability is crucial in the effectiveness of dialysis. Lastly, osmotic pressure is â€Å"the pressure that must be applied to stop the movement of solvent through the membrane† (p. 19 lab manual). Membrane permeability and osmotic pressure is demonstrated by using the dialysis tubing when submerged in distilled water, and the raw egg when immersed in the Karo syrup. Purpose: One goal of this experiment is to understand the differences in freezing points of a pure solvent compared to a solution with salt. Another goal is to â€Å"observe the phenomenon of osmosis and gain a fundamental understanding of the principle on which dialysis is based† (p. 15 lab manual). Procedure (Part 1: Colligative Properties): To begin this experiment a water bath was assembled using a 100 mL beaker, and filling it half way with cool tap water. Then, crushed ice was placed in the remainder of the beaker just below the top. Salt was finally added to the beaker and the solution was stirred well. After, a test tube was filled with distilled water, and the temperature was recorded every 30 seconds until the temperature reading was steady for five consecutive 30 second intervals. Then the same test tube was placed in the ice water bath and the temperature was recorded the same way as it previously was. Once, the temperature was consistent, the test tube was removed from the ice water bath, and emptied in the sink. The same test tube was used, and again filled half way will distilled water, but this time 1/8 teaspoon of salt was added to the tube. This solution was mixed well until all the salt was dissolved. The temperature was then recorded, as it was in the previous steps. The test tube was also submerged into a fresh ice bath, and the temperature was recorded yet again (same as previous steps). Once all of the data was recorded, the solution from the test tube, and the ice bath were emptied in the sink. Data and Observations: Data Table 1: Pure Water and Salt Solution Seconds Distilled H20 Room temp Distilled H20 Ice bath Saltwater Room temp Saltwater Ice bath 0 10 -2 11 -1 30 10 -1 11 -1 60 10 -1 11 -3 90 10 0 11 1 120 10 0 11 0 150 0 0 180 0 0 210 0 0 240 0 As the above tables show, the freezing point of the distilled water, â€Å"pure water†, experienced super cooling, but not exactly how the lab manual explained it would. The temperature dropped to -2 degrees Celsius, but rose back to zero. In the second table, labeled â€Å"Salt Solution†, super cooling was also experienced by the saltwater in the ice bath. This super cooling was â€Å"textbook†, compared to the first super cooling of the distilled water in the ice bath. This was not supposed to happen in that order according to the lab manual. In this part of the experiment we see how non volatile solutes affect the freezing point of the solution. Procedure (Part 2 Osmotic Pressure): To begin this part of the experiment, a glass bowl was filled half way will distilled water. The dialysis tubing was then submerged in the bowl for 30 minutes. After 30 minutes, the dialysis tube was taken out of the bowl and placed on a paper towel. The bowl was emptied in the sink, rinsed with distilled water, and then filled half way again with more distilled water. A rubber band was cut and used to tie off one end of the dialysis tubing, while the other end was filled 1/3 way with Karo syrup. After, the other end of the dialysis tube was tied off with a second rubber band, and the tubing was placed in the distilled water bowl for 10 hours. The dialysis tubing was carefully observed over that time span. The second part of this â€Å"Part 2† was called the â€Å"Raw Egg†. First an intact egg was gently placed into a glass jar. The egg was then covered with vinegar, and the lid was securely fastened for 19 hours. After the shell dissolved completely in the vinegar, the egg was carefully removed from the jar, and rinsed with cool tap water. The glass jar was also emptied into the sink and rinsed thoroughly. From there, the egg was placed back into the jar, and Karo syrup covered it. The lid was again securely fastened for 24 hours. Once all data was recorded, the egg was thrown away in the trash and the syrup was rinsed down the sink. Data and Observations: When the egg was in the jar of vinegar it was observed an hour later, and the egg was floating more than when it was sunken to the bottom at the beginning of the procedure. Over the 19 hour time span, the egg formed a foamy layer on top of the vinegar, due to the egg shell dissolving. The egg also appeared to be bigger than when it was first placed in the vinegar, and the surface of the egg was covered with tiny air bubbles. Once the egg was taken out of the jar, the membrane was soft and slimy, and the shell was completely dissolved. When the egg was in the jar of Karo syrup, the egg was obviously not protected by a shell, so the membrane was soft. Over the 24 hour time span, the syrup started to turn a very yellow tint, and the egg membrane, at first, seemed to be unchanged. Over the hours, the membrane shape was oval but looked to be getting flatted almost as if someone pressed it together from the top and bottom. At the end of the 24 hours, the bottom of the egg was concaved. Questions (Part 1) B. Record the freezing point of the pure water and the freezing point of the salt solution. The freezing point of the pure water is 0 degrees Celsius. (not in this data, the freezing point is -2) The freezing point of the salt solution is -1. C. How do these two freezing points compare? If there was no experimental error in this lab, the freezing point of the salt solution would be lower than that of the pure water. In this case it is the opposite due to error. D. What are some practical applications of freezing point depression, boiling point elevation, and vapor pressure lowering? An example of freezing point depression is when one adds anti-freeze to car fuel to prevent the fuel from freezing in cold temperatures, like we are experiencing in the north east region now. An example of boiling point elevation would be the same. The antifreeze in the car also elevated the temperature of the fuel preventing your car from overheating. An example of vapor pressure lowering would be freeze drying. Freezing occurs because the vapor pressure from the surrounding air is lowered, and causes the substance to freeze. Questions (Part 2) A. To what biological structure is the dialysis bag comparable? How is it similar? How is it different? Cell membranes are comparable to the dialysis bag. They are similar because both are permeable. They differ though because cell membranes are semi permeable; regulating what enters and exits the cell. This is also different because cell membranes regulate what enters and exists on basis of survival. 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? In this experiment the Karo syrup is hypotonic because the egg expanded with Karo syrup. The egg could also be hypertonic, because the Karo syrup seemed to have a yellow tint. The explanation for this could be the yolk of the egg permeating the membrane into the Karo syrup. C. Historically certain colligative properties – freezing point depression, boiling point elevation, and osmotic pressure – have been used to determine molecular mass. (Now there are instrumental methods to determine this. ) Of these three, osmotic pressure is the most sensitive and gives the best results. Molecular mass can be found according the following equation: ? = MRT Where:? = osmotic pressure, M = molarity of solution, R = the ideal gas constant (0. 0821 L? atm/mol? K), and T = Kelvin temperature. Problem for Lab Report: At 23. 6 °C, 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 mm Hg * 1 atm/760 mm Hg = 0. 010973684 atm. 0. 010973684 atm = M ( 0. 0821) (273 + 23. 6); M = 0. 010973684 / (0. 0821 * 296. 6) M = 0. 000450649 = 4. 50 x 10^-4 Molarity = moles / L: 4. 50 x 10^-4 = moles / . 500L (4. 50 x 10^-4) * (0. 500) = moles moles = 0. 000225 = 2. 25 x 10^-4 If 2. 25 x 10^-4 = 0. 302 grams, Then 1 mole = 0. 302g / 2. 25 x 10^-4 = 1342 g/mole which is the molar mass of the antibiotic Conclusion: In conclusion, the first part of the experiment exemplified how freezing points differ when solutes are added to a solvent. This is an important concept to grasp when learning and understanding the boiling and freezing points of many different solutions. In the antifreeze example above, it is extremely important to understand in freezing temperatures. Even though the data in this part of the experiment did not hold true, as explained in the lab manual, we can conclude that the addition of salt; solute, to distilled water; solvent, will cause a super cooling effect to the temperature. Errors could be explained in this portion to human error when reading and recording temperatures. Super cooling happens so rapidly, so this could be a plausible answer to error. Another error that could have explained the data could be due to the amount of salt in the ice water bath. If too much was used it could affect the results. The second part of the experiment helped show membrane permeability, and osmotic pressure of the dialysis tubing and the egg. As stated above permeability and semi permeability are crucial in the effectiveness of dialysis. In this experiment we can conclude that the dialysis tubing was more permeable than the egg. Understanding osmotic pressure is important to understand the rate at which osmosis will occur. In this experiment the osmotic pressure was greater in the dialysis tubing, than the egg.