Dave Morneau
1/11/10
Teacher Instructions
Objectives: Show a basic chemical reaction, starch and iodine to create an
invisible ink and show the beginning of digestion.
First Experiment:
Materials
- cornstarch
-2 cups
-iodine solution (Warning: do not eat; avoid eye contact) (can be purchased at
drug store)
Have students mix water and cornstarch in a cup and then add iodine solution to
it. The solution will turn a dark purple. This will show that iodine, when in the
presence of starch, turns purple, the basis of the other two experiments.
Second Experiment:
Materials
-crackers (three for each student/group)
-iodine solution (Warning: do not eat; avoid eye contact) (can be purchased at
drug store)
-paper plates/ paper towels
Give each student three crackers. Have the students crumble up one of the
crackers, keep one untouched and have the other one be chewed up well and
then spit out. This is best done on a paper plate. Then add drops of iodine to
each of the three crackers, or have students do this (iodine can be harmful if
eaten) make sure this is clear that the crackers cannot be eaten after iodine is
added.
The untouched cracker should show no change. The crumbled cracker will show
purple as iodine and starch will form this color. The chewed cracker will not show
this purple because saliva converts starch to sugar. The cracker must be chewed
well to make sure most starch is converted.
Third Experiment
Invisible ink
Materials
-starchless paper
-cornstarch
1
-iodine solution (Warning: do not eat; avoid eye contact) (can be purchased at
drug store)
-paint brush
-q-tips
-beaker
Have each student create a cornstarch/ water mixture and then write a message
using the q-tip on a piece of paper. Let the message dry and then lightly paint
over the paper with iodine and watch the message appear in nice purple color
From
Exp 2:
www.coolscience.org/coolscience/kidscientist/iodinestarch.htm
Exp 3:
Page 180 of Championship Science Fair Projects by Sudipta Bardhan-Quallen
2
Name___________________________
Date_______________
Let’s begin!
1. In one cup put water and the other water and corn starch
2. Add iodine solution to each one
3. Draw what you happens
How does food change as you eat it?
1. Get three crackers and place them on a paper towel
2. Crumble the middle cracker with your hand
3.
Chew one of the others and spit it out
Spit
out!
4. Add iodine drops to each
What happens to each? Write down what happened
Cracker?
Cracker crumbs?
Spit out cracker?
Spit
out!
The spit out cracker acts differently than the chewed one because your spit
begins breaking down starch in the cracker. You begin digesting food before it
reaches your stomach
Invisible Ink
1. Mix cornstarch with water in a cup
2. Use q-tip to write a message on a piece of paper
3. Let your message dry
4. Softly paint iodine over to reveal the message
Notice how the message turns the same color as the crumbled cracker when the
iodine is added
1
Why do you think this is?
2
2