Kristina Eskola
BL 1020
L01
Diffusion and Osmosis Lab Report (Dialysis)
Introduction:
Dialysis Tubing is a membrane made of regenerated cellulose fibers formed into a flat tube. If two solutions containing dissolved substances of different molecular weights are separated by this membrane, some substances may readily pass through the pores of the membrane, but others may be excluded.
We will be investigating the selective permeability of the tubing to reduce sugar, glucose, starch, and iodine potassium iodide. We will test this by placing a solution of glucose and starch into a dialysis tubing bag and then place this bag into a solution of iodine potassium iodide (I2KI).
Prediction: The I2KI solution will turn blue when adding Benedict’s reagent.
Hypothesis: The solution of water and I2KI will be the most permeable because they will mix and react with Benedict’s reagent and the heat so the cell membrane only allows certain molecules to enter and leave the cell
Materials and Methods: In the experiment we will be using two tests. In the first test, we will be using I2KI to test for the presence of starch. When I2KI is added to an unknown solution, the solution will turn purple or black if starch is present. If there is no starch in the solution, it will remain pale yellow. In the second test we will be using Benedict’s test for reducing sugar. When Benedict’s reagent is added to an unknown solution and the solution is heated, it will turn green, orange or orange-red if sugar is present. If no sugar is present in the solution, it will remain blue. The materials needed for this experiment are the 30% glucose substance, starch solution, I2KI solution, Benedict’s reagent, hot plate, 500 mL beaker with water, test tube holder, 3 test tubes, pipettes, 2 400 mL beakers, and a strip of moist dialysis tubing.
Procedure: The first thing we did was prepare the dialysis bag with the initial solutions. We added 4 pipettes of 30% glucose and 4 pipettes of starch to the bag. We then recorded its color. Then we added 300 mL to the beaker. Then added several drops of I2KI solution until the water was yellow, and then recorded its color. Then the dialysis bag was placed into the beaker with the H2O and I2KI solution. Let the bag sit for 30 minutes then took it out and placed it in a dry beaker and recorded its color. For the second test we had 3 test tubes labeled control, bag, and beaker. The control tube had 2 pipettes of water, the bag tube had 2 pipettes of solution from the bag, and the beaker tube had 2 pipettes of solution from the beaker. We added 1 dropper full of Benedict’s reagent to each tube. We then heated the test tubes in boiling water for 3 minutes and recorded the results.
Results:
The table below shows all results recorded during the experiment. SolutionSource | Original Contents | Original Color | Final Color | Color after Benedict’s test | Bag | 30% glucose and starch solution | Cloudy, Milky, White | Blue | Regular yellow | Beaker | H2O and I2KI Solution | Amber yellow | Amber yellow | Dark yellow, orange-red tint. | Control | H2O | Clear | Clear | Clear with blue tint |

In the control tube it had plain water to it was clear and nothing happened until we added the Benedict’s reagent, it had a little tint of blue to it. The bag with glucose and starch mixed to form a cloudy, milky, and white solution. When we added Benedict’s reagent it turned the solution blue. When it was boiled on the hot plate for 3 minutes, the color changed to yellow. The beaker with H2O and I2KI mixed to form an amber yellow solution. After Benedict’s reagent was added and it was boiled for 3 minutes, the color changes to a dark yellow with an orange-red tint. All of these results are shown in the table above.
Discussion:
In the beginning of this experiment I predicted that the I2KI solution will turn blue when adding Benedict’s reagent. I was wrong in this prediction. It turned a dark yellow with an orange-red tint. My hypothesis was the solution of water and I2KI will be the most permeable because they will mix and react with Benedict’s reagent and the heat so the cell membrane only allows certain molecules to enter and leave the cell. In this experiment we proved that when Benedict’s reagent was added and solutions were boiled, all the colors changed. This is significant because it means they reacted with the reagent and the heat to form something different. It also means they are permeable because they are letting only certain molecules in and out, either causing them to stay the same color, or causing them to change and become a different color. From my results I would predict that the I2KI molecules are larger than the glucose and starch. From this experiment, if it started with glucose and I2KI in the bag and starch in the beaker, the bag would be yellow and the beaker would be a blue tint.
Acknowledgments:
I would like to acknowledge my lab partners and also my lab TA for the help given through this experiment to help complete it.