chemistry lab

Unit 8 Lab: Colligative Properties and Osmotic Pressure

CHEM 1806

Purpose: To observe freezing point depression and Osmotic pressure

Materials: Student Supplied – Karo Syrup, Salt, Distilled water, Vinegar, Egg, Ice, Glass, Measuring spoon

LabPaq materials: Test Tube, Thermometer, 100mL plastic beaker, 24-well plate

Procedure: Start the Osmotic Pressure procedure several days before the due date!

Freezing Point Depression

1. Place ice water in 100mL beaker, up to the 100mL mark. (not precise)

2. Add “some” salt to the ice water. This cools the water down faster. (Mythbusters proved this once. )

3. Fill the test tube about half way with distilled water and insert the thermometer.

4. Place the test tube assembly in the 24-well plate as a secure place to hold the test tube.

5. Read the thermometer, to the hundredths place, until the temperature is stable. Record in Table 1 below. Add rows to the table as needed.

6. Place the test tube assembly into the beaker of ice water.

7. Start the stop watch and take temperature readings every 30 seconds until the temperature remains constant. (Remember to read the thermometer to the hundredths place!) you might see the temperature cool rapidly to -2 or -3 then rise to 0C. That is expected. Continue to record 5 temperatures after that rise occurs.

8. Dump out the cold water and refill the test tube half way with room temperature distilled water.

9. Carefully add 1/8 teaspoon of table salt to the test tube. (The salt won’t dissolve as much in cold water, so it is best to restart with warmer water.)

10. Stir gently with the thermometer and take readings, as in #5, until the temperature is constant. Record these temperatures in Table 2 below.

11. Place the test tube assembly in the beaker of ice water.

12. Start the stop watch and take temperature readings every 30 seconds until the temperature remains constant. (Remember to read the thermometer to the hundredths place!)

You will graph this data in the Results & Discussion section.

Osmotic Pressure

1. Record physical observations of the egg in table 3. (Shape, color, texture, etc.)

2. Gently place the egg in a small glass (that it fits in) and cover the egg with Vinegar.

3. Make observations of the physical characteristics of the egg over the next 24 hours.

4. Record observations in Table 3.

5. Once the shell has been dissolved, gently remove the egg and record additional physical observations.

6. Rinse the egg and the glass with tap water (BE VERY CAREFUL not to break the membrane!) and replace the egg in the glass.

7. Cover the egg with light corn syrup (Karo is the only one we tested).

8. Observe the egg in corn syrup for 24-48 hours.

9. Record the observations

Data: (4pts)

Table 1: Temperature Readings - distilled water

Time lapsed	Temperature of TestTube	Temperature of Test Tube in Ice water

Table 2: Temperature Readings - Salted - distilled water

Time lapsed	Temperature of TestTube	Temperature of Test Tube in Ice water

Table 3: Egg observations

Initial Observations:

Time Lapsed: hours Observations:

Time Lapsed: hours Observations:

Time Lapsed: hours Observations:

Shell removed Observations:

Egg in Karo syrup

Time Lapsed: hours Observations:

Time Lapsed: hours Observations:

Time Lapsed: hours Observations:

Final Observations:

Results and Discussion:

1. (2pts)Graph your temperature observations in the ice water bath. Insert those graphs here. (temperature on y axis, time on x)

a. Distilled water results

b. Salted distilled water results

2. (2 pts)Draw a best fit line in the linear portions of the curves. The intersection of these linear portions on each graph is the freezing point.

i.e.

Where the Orange and blue lines intersect is the freezing point for this graph. You may estimate with a best guess.

Report your freezing point for Distilled water here:

Report your freezing point for Salted Distilled water here:

3. (2 pts) Explain why these freezing points are the same or different.

4. (5 pts) In the Osmotic pressure portion of the lab, the egg should have changed after it sat in the Karo syrup. Summarize the change you saw and explain why this occurred. Include in your summary whether the corn syrup was hypotonic or hypertonic to the egg. Hypotonic is when the concentration of the solution is lower than the cell system (egg, in this case); Hypertonic is when the concentration of the solution is higher than the cell system. Reason this out. (Complete sentences and show thought.)

5. (5pts) Insert a picture of your egg after it sat in the Corn Syrup.

When you are finished, save the file as LASTNAME_Colligative and upload it to the Dropbox for Unit 8 Labs.