Diffusion of Iodine and Starch through the Semi-Permeable Membrane of a Visking Tubing.

Methodology

1. Place Heatproof Mat on a flat surface and place Bunsen burner onto the mat, ensure the Bunsen burner is open so the flame is visible whilst lighting, close the Bunsen burner off so it becomes a blue flame and place Tripod and Gauze over the Bunsen burner.
2. Fill a beaker with 200mls of Water.
3. Weigh 1g of Starch and place into the beaker of Water
4. Place the beaker on top of the heat and with the stirrer continuously stir the solution until it is clear.
5. Once clear remove the beaker from the heat and allow cooling for approximately 10 minutes.
6. Whilst allowing the solution to cool, fill another beaker with 200mls of Water.
7. Tie a knot at one end of the Visking Tubing and rinse under water to ensure it is clean; lightly rub the top to gently open the Visking Tubing.
8. Using a pipette, fill the Visking Tubing with the cooled down Starch Solution and tie a knot in the top of the Visking Tubing, ensure the outside remains clean for fair results.
9. Place the Visking Tubing into the Beaker of 200mls of water and add 10 drops of Iodine Solution or until the water is yellow.
10. Record results.

Results

Based on the observations the Iodine moved into the Visking Tubing turning the solution purple/black, whereas the Starch stayed in the same place.

Conclusion

In the experiment it was investigated to see whether large Starch molecules are too large to pass through the semi-permeable membrane, but Iodine is small enough to pass through the membrane, as the results table show after 15 minutes of observation, Iodine passed through the semi permeable Visking Tubing into the Starch, which once Iodine and Starch are together they react and go a purple/black colour, whereas the beaker stayed a yellowish colour.

This shows that the Starch Molecule could not pass through the Semi permeable membrane as it was too large and the Iodine which is an atom was small enough to pass through the membrane to react with the Starch which caused the colour change as the results shown.

The hypothesis is accepted. Substances consisting of small molecules can move across the semi-permeable membrane (Visking tubing).

Evaluation

If the experiment were to be carried out again there are certain things that could be changed these could include:

• The amount of Iodine drops used.
• Checking temperature accurately.
• Using stopwatch to record times.
• Use the same amount of Starch Solution in each Visking Tubing.