Colligative Properties

Topics: Freezing-point depression, Water, Osmotic pressure Pages: 5 (1437 words) Published: February 7, 2015


Cognitive Properties
Ashley Weber
Principles of Chemistry 2
Experiment 1
02/02/2015

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...
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