I seem to be having trouble with what should be a simple prac. It has worked beautifully every other year.
I Put starch solution in dialysis tubing and tied off the ends. Put this in a beaker of water. Add iodine solution to the water in the beaker. Iodine should diffuse into the bag and make the starch go black.
Didn't work the first time the students tried it. Decided starch solution was too weak. Then made up a really strong solution of starch and put this in a dialysis bag and put the bag into a beaker of water with a few squirts of iodine solution. Also Tested the starch solution and iodine in a beaker by putting a drop of iodine directly into the starch and it turned black. But no turning of starch black inside the dialysis bag.
Tried putting lots of squirts of iodine solution directly into the dialysis bags (students not watching at the time). Turned pinky browny black at the time but by the time the students went to check, the starch that had settled on the bottom was white again.
I just tried putting putting a few drops of iodine solution directly into starch solution in a beaker again. Turned black where the iodine contacted the starch. Left it to sit for awhile. Starch settled to the bottom and showed two pinky smudges that were barely visible.
Where is my problem?
The starch solution?
the dialysis tubing?
the iodine solution?
ps glucose moved through the dialysis tubing very well. That part of the experiment did work well.
Any thoughts would be appreciated. We need to do the prac again with another class next week.
Thanks
Tina
