Starch and Iodine Lab


I am studying the process of diffusion and how iodine is affected by a semi-permeable membrane filled with starch. I am studying this lab to watch and see how diffusion works. This topic is important because in order to survive our cells need to be able to transport materials into and out of our cells. One way of bringing materials into and out of the cell is through the process of diffusion. I already know that diffusion is the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration. I also know that diffusion is a type of passive transport- a type of movement of molecules across a cell membrane without energy input from the cell. I have observed food coloring diffusing through various types of water.

Sugars provide living things with energy. All carbohydrates are sugars. Starch is a complex carbohydrate made up of simple sugars. Starch is the polymer of a monosaccharide (one sugar) , glucose (the simplest sugar). This means that the complex carbohydrates are units of sugar bonded together in large chains. Some  examples of starch are: corn, peas, potatoes and winter squash, and breads.


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



If iodine travels through a semi-permeable membrane, then diffusion will occur and the starch will turn into the tea-color.



  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 predict that the  iodine will diffuse through the dialysis tube and react with the starch, causing the starch to become the “tea” color.





According to my hypothesis, iodine would travel through a semi-permeable membrane and it would turn the liquid inside the dialysis tube a tea-color. My hypothesis was incorrect. Iodine travels through a semi-permeable membrane because iodine molecules are smaller than starch molecules. Since we were unable to achieve results from our experiment, we used data from another class to complete this lab. Since iodine molecules are small, they are able to diffuse across the semi-permeable membrane from an area of high concentration to an area of low concentration turning the liquid (starch) dark purple. The starch molecule was too big to pass across the semi-permeable membrane so the liquid outside the membrane remained clear. Errors occurred because we were unable to tie the dialysis tube tight enough, which caused it to leak. In addition, there could have been a measurement error putting in too little or too much iodine or starch. If I were to repeat this experiment I would conduct multiple trials, and I would allow more time setting up the experiment (sealing the tubing) to get more accurate results.

2 thoughts on “Starch and Iodine Lab

  1. great background; just add how we will use starch and iodine to test diffusion in the lab

    excellent; yours is example worthy


Leave a Reply

Your email address will not be published. Required fields are marked *