Praxis: Testing for starch

By Medicine Hat News on September 22, 2018.

What a week it has been as we celebrated Science Literacy Week in Canada! We had a great start with a number of students attending our “Science Fair How To” at the Medicine Hat Public Library and we ended with a bang (literally!) with a full house of preschool scientists! It was an amazing group of students and it always excites me to see such enthusiasm from our youth in the city. To end the week, I thought we would share one of our favorite experiments to do at home. Let’s get started!

*Remember to ask an adult to help you with this experiment.

Materials

– potatoes

– tincture of iodine *poisonous*

– apples

– cornstarch solution (you will make this below)

– distilled water

– newsprint

– eye droppers

– knife or scalpel

– rubber gloves

– plate or dish

– safety goggles

– empty plastic container

– measuring cup

– measuring spoon

Procedure I

Making a Starch Solution

1. Mix two tablespoons (30 mL) of cornstarch with four tablespoons (60 mL) of cold water. It should make a paste.

2. Fill a kettle with distilled water and bring to a boil.

3. Measure one quarter of a cup (60 mL) of water.

4. Pour the boiling water into a bowl.

5. Slowly stir in the cornstarch mixture.

6. Stir well and quickly as it may form lumps.

7. Set aside and allow to cool.

Procedure II

1. Put on your rubber gloves and safety goggles.

2. Cover your work area with a couple of layers of newsprint. Iodine can be very messy and will stain anything that it touches.

3. Cut a piece of raw potato and set aside.

4. Cut a piece of apple and set aside.

5. Place one quarter of a cup (60 mL) of distilled water into a plastic container and set aside.

6. Place one drop of iodine in the distilled water. What do you see?

7. Repeat No. 5 for the apple, potato, and cornstarch solution. What do you see?

What is going on?

Iodine is often used as a test for starch. When you placed the iodine in the distilled water, the control, it should have been a yellowish brown colour. This means that there is no starch in the water. You should have seen a bluish black colour when you placed the iodine in the cornstarch solution. This caused a chemical reaction between the starch and the iodine. The apple and the potato should have also turned bluish black because they also have starch in them.

Try this experiment with other materials you can think of. Do they contain starch?

Patty Rooks is senior scientific consultant at PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook.

39
-38