Using Dialysis Bags to Investigate Osmosis

Introduction:

In this experiment you will use dialysis tubing to investigate the relationship between solute concentration and the movement of water through a selectively permeable membrane by the process of osmosis.

When two solution have the same concentration of solutes, they are said to be isotonic to each other (iso-means same, -ton means condition, -ic means pertaining to). If the two solutions are separated by a selectively permeable membrane, water will move between the two solutions until dynamic equilibrium is reached. There will be no net change in the amount of water in either solution.

If two solutions differ in the concentration of solutes that each has, the one with more solute is hypertonic to the one with less solute (hyper-means over, or more than). The solution that has less solute is hypotonic to the one with more solute (hypo-means under, or less than). These words can only be used to compare solutions.

Now consider two solutions separated by a selectively permeable membrane. The solution that is hypertonic to the other must have more solute and therefore less water. At standard atmospheric pressure, the water potential of the hypertonic solution is less that the water potential of the hypotonic solution, so the net movement of water will be from the hypotonic solution into the hypertonic solution.

Hypothesis:______

Procedure:

• Each group will be assigned one of the five sucrose concentrations (0.0M, 0.2M, 0.4M, 0.6M, and 0.8M)
1. Tie a knot in one end of a strip of dialysis tubing (selective permeable membrane “cell”).
2. Using a funnel, fill the bag with 15 mL your assigned sucrose solution. Tie a knot in the other end of the tubing, leaving ample space between the sucrose and your knot.
3. Blot the tubing dry with paper towel.
4. Tare “zero” a solo cup on the electronic balance. Do not remove the cup from the electronic balance.
5. Place your tubing inside the solo cup that is located on the electronic balance.
6. Record the mass of the dialysis tubing on your data table.
7. Place each dialysis bag in a separate cup after obtaining the individual masses.
8. Fill each plastic container about 2/3 full of distilled water. Be sure each bag is submerged in the water.
9. Let the bags stand for 30 minutes.
10. At the end of 30 minutes, measure the mass of your dialysis tube. Remember to tare the cup and place the dialysis tube directly in the cup when taking the mass.
11. Record your data on your data table 1. Record the class data on data table 2

Data Table 1: Dialysis Bag Results (Group Data)

Contents in Dialysis Bag / Initial Mass / Final Mass / Mass Difference
(Final Mass-Initial Mass) / Percent Change in Mass *
0.0M Distilled Water (Clear)
0.2M Sucrose (Yellow)
0.4M Sucrose (Green)
0.6M Sucrose (Red)
0.8M Sucrose (Blue)

* To calculate: Percent Change in Mass = (Final Mass- Initial Mass)* 100

(Initial Mass)

Data Table 2: Dialysis Bag Results (Class Data)- % Change in mass

Group 1 / Group 2 / Group 3 / Group 4 / Group 5 / Total / Class Average
0.0M Distilled Water (Clear)
0.2M Sucrose (Yellow)
0.4M Sucrose (Green)
0.6M Sucrose (Red)
0.8M Sucrose (Blue)

Graphing Results of Data:

1. Graph the results for the class average data on Graph 1

For this graph you will need to determine the following:

1. The independent variable: ______

Use this to label the horizontal (x) axis

1. The dependent variable: ______

Use this to label the vertical (y) axis

Title: ______

Analysis of Results:

1. How is the % change in mass related to the molarity of sucrose within the dialysis bags?
1. Predict what would happen to the mass of each bag, and movement of water in this experiment if all the bags were placed in a 0.4M sucrose solution instead of distilled water. Identify the type of solution for each container.
1. Why did you calculate the percent change in mass rather than simply using the change in mass?
1. A dialysis bag is filled with distilled water and then placed in a sucrose solution. The bag’s initial mass is 20g and its final mass is 18g. Calculate the percent change of mass, showing your calculations here.
1. The sucrose solution in the beaker would have been ______to the distilled water in the bag. (Circle the word that best completes the sentence.)

Isotonichypertonichypotonic

1