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Why Does The Indicator Change Colors?
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Science Area:  Life Science
Concept:  Iodine Starch Test

 Iodine Starch Test     

 

Materials:

Iodine

Dropper

Paper plates

Samples of various foods such as a cooked egg, an onion, an apple, bread, crackers

 

 

Safety Considerations:

 Be careful with the iodine.  It is toxic by ingestion and do not use near fire.

Iodine can also irritate the eyes and can temporarily stain skin. 

 

Discrepancy:

Students will not expect the food to change colors when it comes in contact with the Iodine.

 

Procedures:

 

Place each specimen of food onto a paper plate.

Place a drop of iodine on a food that doesn’t contain starch (such apple, or onion).

This will be your control group.

Next ask the class what will happen if you drop the iodine on the bread or cracker.

Drop the iodine onto the bread or cracker

Observe

 

Questions:

1.  What do think will happen (predictions).

2.  Why does the color change occur with some foods and not others?

 

3.  What do all of these foods have in common that may be causing the color change?

 

4.  Once you have done a few, ask students to predict which foods will change and which ones will not.

 

Explanation:

 

The iodine acts as an indicator and reacts with the starch in the foods to cause a color change.  Starch is a complex carbohydrate that your body breaks down into simple sugars for energy.  

 

 

Source:  Bilash, Borislaw and Shields, Martin. A Demo A Day.  Flinn Scientific.  Batavia, IL. 2001.  p.42-43.