Praxis: Starch testing

By Medicine Hat News on October 20, 2018.

It is that time of the year, I need to get out and dig my potatoes from the garden. Despite the weather, it appears that this was a great year to grow potatoes as there is an abundance out in the garden! In order to help use up some of these potatoes, I thought I would come up with a fun experiment to do. Let’s get started!

*Remember to ask an adult before doing this experiment. Caution: Iodine is used in this experiment, which is poisonous. When doing this experiment, adults should be present to ensure the iodine is used correctly.

Materials

– potato

– tincture of iodine *poisonous*

– other fruits and vegetables

– distilled water

– newsprint

– medicine dropper

– knife

– rubber gloves

– plate

– safety goggles

– empty plastic container

– measuring cups

Procedure

Put on your rubber gloves and safety goggles. Trust me, the iodine will stain your hands!

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

Slice the potato into several slices. Lay these out flat on the plate.

Using a dropper, place a couple of drops of iodine onto one of the potato slices.

Observe. What happens?

Measure 1/4 cup of distilled water into a plastic container.

Place a couple of drops of iodine into the distilled water.

Observe. What do you see?

Try this with other fruits and vegetables or other food products from around the kitchen.

Observe.

Repeat for the apple, potato, and cornstarch solution. What do you see?

Explanation

In science class, you may have used iodine to do some testing. Iodine is often used as a test for starch.

In this experiment, 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.

When you placed the iodine drops onto the potato, it should have turned bluish black. This is because there was a chemical reaction between the starch and the iodine.

Depending on the vegetables and fruit you try, they will also turn bluish black if they contain starch. You may be surprised to see what contains 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.

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