Access the Student Journal for Activity 5
Materials Needed :
1
beaker/plastic cup per group (3 groups total)
Corn starch
Tincture of
Iodine (important: must be tincture of iodine)
Plastic sandwich bags- cheap is
best (not the kind that zip shut)
1 spoon
Measuring cup or 50mL syringe
Eye dropper
Water
Timer or Clock
Activity #5 - Properties of Diffusion
1. Fill your beaker or plastic cup with about 1 cup (240mL) of water.
2. Place a spoonful of starch into your plastic bag. Make sure not to spill any of the starch on the outside of the bag. Put 50mL of water in the plastic bag. Try to get as much air out of the bag as possible without spilling any of the solution and then tie the bag so it will not leak. Be careful not to put too much pressure on the bag or it might tear.
3. Using the eye dropper, place the number of drops of iodine into the water as directed by your teacher (10, 25, or 50).
4. Place the bag with the starch solution into the beaker, making sure that the starch solution is covered by the iodine mixture.
5. Watch the solution for 10 minutes and record what happens.
6. Record your findings for 10 minutes. Note:
When did an initial color change occur?
What was the final color of the starch solution?
How much of the solution turned color?
Discussion:
1. Why did the starch solution change color?
2. Why didn’t the water in the beaker change color?
3. Which substance is the plastic bag permeable to?
4. How is the plastic bag like the cell membrane? How is it
different from the cell
membrane?
5. How did changing the concentration of the iodine solution affect
the color of the
starch solution and affect the time in which the
starch solution changed color? Why?
TEACHER NOTES:
If you need additional groups, you may want additional varying concentrations or vary the concentration of the starch solution in the bags. Make sure each group gets to see what the other groups did and compare results.
Experiment designed by JeanMarie Stanley, Texas A&M University