Modeling Diffusion and Osmosis

Procedure 2: Modeling Diffusion and Osmosis Lab

 

Introduction:

In this lab, my partner and I were required to models of living cells using dialysis tubing. The tubing serves as a selectively permeable membrane to water and some solutes. We were required to get multiple bags to place a total of 3 different solutions and they were soon each placed into 3 different beakers with different solutions as well. These solutions consisted of ovalbumin, sodium chloride, and glucose. The dialysis tubing is a replica of the inside of the cell, while the beaker serves as the outside of the cell. The purpose of this experiment is to observe the rate and direction of water.

Materials:

  • 1 M Sucrose
  • 1 M NaCl
  • 1M Glucose
  • 5% Ovalbumin (Egg White Protein) 0.002M
  • 20 cm-long Dialysis Tubing
  • A Scale
  • Beakers or Cups

Procedures:

  • Refer back to the lab packet

Hypothesis:

Null Hypothesis: All solutions diffuse in the same direction and at the same rate.

Experimental Hypothesis: If the ovalbumin were to be placed in a beaker containing sodium chloride for 15 minutes, then the sample will diffuse into the bag causing a change in weight as well. When the sodium chloride is placed into a beaker containing sucrose for 15 minutes, then the content within the bag will diffuse out of the bag and create a change in weight. When the glucose in dialysis tubing is placed into a beaker with ovalbumin, then the glucose will move out of the bag and decrease the weight inside the bag.

Data and Observations:

Time

Dialysis Tubing Contents

(8 mL)

Temperature

Color

Beaker

Contents  (50 mL)

Temperature

Color

Start

Ovalbumin

13 C

Yellow

NaCl

22 C

Clear

NaCl

22 C

Clear

Sucrose

22 C

Clear

Glucose

22 C

Clear

Ovalbumin

13 C

Yellow

After 30 Minutes

Ovalbumin

13 C

Cloudy white/gray

NaCl

22 C

Yellow

NaCl

22 C

Clear

Sucrose

22 C

Clear

Glucose

22 C

Clear

Ovalbumin

13 C

Clear

 

Solution in the Dialysis Tubing

Initial Weight

(In grams)

Final Weight

(In grams)

Change in Mass

(In grams)

Percent Change in Mass

Ovalbumin

8.08 g

7.69 g

– 0.39 g

-5 %

NaCl

8.00 g

7.98 g

– 0.02 g

-.25%

Glucose

7.30 g

5.86 g

– 1.44 g

-20%

Independent Variable:

Water Potential

Dependent Variable:

Weight

Analysis:

                                   Water Potential = Water solute + Water pressure

Water solute= -ionization x concentration x r x temperature

 

  •  NaCl (outside):          -(2)(1)(0.0831)(295)            = -49.029

-49.029 + 1 atm = -48.029

Ovalbumin (inside): -(1)(0.002)(0.0831)(286)   = -0.0475332

-0.0475332 + 1 atm = 0.9524668

  • Sucrose (outside):     -(1)(1)(0.0831)(295)           = -24.5145

-24.5145 + 1 atm = -23.5145

NaCl (inside):             -(2)(1)(0.0831)(295)            = -49.029

 -49.029 + 1 atm = -48.029

  • Ovalbumin (inside): -(1)(0.002)(0.0831)(286)   = -0.0475332

-0.0475332 + 1 atm = 0.9524668

Glucose (outside):     -(1)(1)(0.0831)(295)           = -24.5145

-24.5145 + 1 atm = -23. 5145

 As you can see, none of the solutions within the dialysis tubing increased in mass after they were each put into different solutions. However, the third pairing of solutions, glucose on the inside and ovalbumin on the outside, received a significant amount of change in mass. Also, in each of the solutions water moved out of the bag and this is observed by the shrinkage of the contents within the bag and the water potential calculations, where the water is supposed to move from a high concentration on onto a lower concentration.

Conclusion: 

            Each of the solutions: glucose, sodium chloride, and ovalbumin move in the same direction and at the same rate. For the first pairing, the sodium chloride went from a water potential of -48.029 to a water potential of 0.9524668, in the second pairing, sucrose moved from a water potential of -23.5145 to a water potential of -48.029, and for the final pairing the ovalbumin moved form a water potential of 0.9524668 to a water potential of -23.5145. Unfortunately, only the pairings of sucrose with sodium chloride and ovalbumin with glucose proved to move from higher water potential to a lower one. However, because our experiment was controlled to 30 minutes, the rate of movement was not a factor when calculating water potential. The pairings of sucrose/NaCl and glucose/ovalbumin moved from a higher water potential to a lower water potential when the calculations were conducted, although our actual experiment proved that in each of the solutions, the water moved outside of the dialysis tube and acted as a hypotonic solution (or the cell shrunk). Although ultimately the null hypothesis was supposed to be proven wrong, factors such as the length of time some of the solutions have been sitting out and the breaking down of those solutions could have possibly affected the results of our experiment somehow.

 

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