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Starch and iodine lab

October 21, 2011 by christie24 · 1 Comment · Uncategorized


Starches are found in potatoes, a type of plant that contains carbohydrates. The topic is important because it shows how starch can change over time:)


Does starch or iodine travel through a semi-permeable membrane (dialysis tubing)?


If iodine travels through a semi-permeable membrane, then it will dissolve into the starch.


  1. Soak dialysis tubing in water for approximately 2 minutes.
  2. Open dialysis tubing by placing between fingers and moving fingers back-and-forth.
  3. Tie dialysis tube by twisting, folding and using piece of string approximately 2 cm from edge.
  4. Add 8mL of starch solution to dialysis tube.
  5. Seal second end of dialysis tube by repeating Step 3.
  6. Rinse dialysis tube well with water and dry gently.
  7. Fill 250mL beaker with 200ml of water.
  8. Add drops of idoine until the soluiton is “tea” color, approximately 20 drops.
  9. Place dialysis tube in the beaker and let sit for 20 minutes.
  10. Record observations every 5 minutes.



I think that the starch will start to bubble up.


If iodine travels through a semi-permeable membrane, then it will dissolve into the starch. My hypothesis was correct. Starch and iodine does not travel through a semi-permiable membrane. The color from the starch did not leake through dialysis tube, there was no colored water, it was clear. It took 4 days  for the changes to occur in the beaker. A way to improve this experiment is to tie the ends of the dialysis bag tighter.



Quantitative (#)observasions   filled beaker with 250

ml of water

 used 20 drops of iodine
 Qualatative(words) Observations  took 4 days for changes to occur  the liquid in the daysis tube turned dark purple

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One Comment so far ↓

  • drott22

    background is not complete; hypothesis was correct, but your statement that it didn’t occur is incorrect; we know iodine moved across the membrane because the starch turned purple; more discussion of modifications and error

    T: 4
    C: 1

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