EXERCISE 1B: Osmosis


Materials:

As indicated in the procedure.

Procedure:

  1. Obtain one 15-cm strip of presoaked dialysis tubing. If you are doing the lab alone you will need 6 strips of dialysis tubing.
  2. Tie off one end of your piece of dialysis tubing to form a bag. Pour 10 mL of one of the following solutions into this bag. The choice of solution depends upon where your lab station is.

    a)

    distilled water

    b)

    0.2-M sucrose

    c)

    0.4-M sucrose

    d)

    0.6-M sucrose

    e)

    0.8-M sucrose

    f)

    l .0-M sucrose

  3. Remove most of the air from the bag by drawing the dialysis bag between two fingers. Tie off the other end of the bag leaving sufficient space for the expansion of the contents in the bag. (The solution should fill only about one-third to one-half of the piece of tubing.)
  4. Rinse each bag gently with tap water to remove any sucrose spilled during filling
  5. Carefully blot the outside of the bag and record its initial mass (grams) in Table 1.2.
  6. Fill a 100-mL beaker or cup two-thirds full with distilled water.
  7. Immerse the bag in the beaker of distilled H2O and label the beaker to indicate the molarity of the solution in the dialysis bag.
  8. Let stand for 30 minutes.
  9. At the end of 30 minutes remove the bag from the water. Carefully blot and determine the mass the bag.
  10. Record data in Table 1.2 and graph the group results in Figure 1.1. (See Appendix for a discussion of graphing.)

 

Table 1.2: Dialysis Bag Results: Individual Data

Contents in Dialysis Bag
Initial Mass
Final Mass
Mass Difference
Percent Change in Mass*

a) distilled water

.

.

.

.

b) 0.2-M sucrose

.

.

.

.

c) 0.4-M sucrose

.

.

.

.

d) 0.6-M sucrose

.

.

.

.

e) 0.8-M sucrose

.

.

.

.

f) 1.0-M sucrose

.

.

.

.

* To Calculate:

Graph of Result on Separate Page. Graph the results for both your individual group data and the class average. For this graph you will need to determine the following:

  1. The independent variable using this to label the horizontal (X) axis _______________________
  2. The dependent variable using this to label the vertical (Y) axis ____________________________

Analysis of Results

1. Explain the relationship between the increase in mass and the molarity of sucrose within the dialysis bags?

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2. Predict what would happen in an experiment if all the bags were placed in a 0.4-M sucrose solution instead of distilled water?

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3. Why did you calculate the percent change in mass rather than simply using the change in mass?

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4. A dialysis bag is filled with distilled water and then placed in a sucrose solution. The bag's initial mass is 20 g, and its final mass is 18 g. Calculate the percent change of mass, showing your calculations in the space below.