Lab Manual - eScience Labs

Lab 6: Diffusion
Experiment 2: Concentraon Gradients and Membrane Permeability
We will dialyze a soluon of glucose and starch to observe:
• The direconal movement of glucose and starch.
• The effect of a selecvely permeable membrane.
In this lab, we will be using an indicator to test for the presence of starch and glucose. An indicator is a
substance that changes color when in the presence of the substance it indicates
Materials
Glucose soluon
(M.W.=180g/mol)
1% Starch soluon
(M.W.=>15,000g/mol)
Iodine-Potassium iodide (IKI)
4 Glucose test strips
15cm Dialysis tubing**
4 100mL Beakers
4 Small rubber bands
7 Graduated pipees
Water*
Watch*
*You must provide
** Cut to exact length
Note:
• You will need dialysis tubing in subsequent experiments, so be sure to cut the amount
specified in the direcons.
• Dialysis tubing can be rinsed and used again if you make a mistake.
• Dialysis tubing must be soaked in water before you will be able to open it up to create
the dialysis “bag”. Follow the direcons for the experiment, beginning with soaking the
tubing in a beaker of water. Then, place the dialysis tubing between your thumb and
forefinger and rub the two digits together in a shearing manner. This should open up
the "tube" so you can fill it with the different soluons.
Procedure
1. Fill one 100mL beaker with 50mL water and submerge the dialysis tube for 10 minutes. Fill a
second beaker with 80mL water (this is the one you will put the filled dialysis bag into in Step
9).
2. Aer the ten minutes have passed, remove the dialysis tube and close one end by folding over
3cm of one end (boom). Fold it again and secure with a rubber band (use two if necessary).
3. Make sure the closed end will not allow a soluon to leak out. You can test this by adding a few
drops of water and looking for leakage. Pour the water out before connuing.
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