Academic journal article Teaching Science

Try This: Breaking Stains

Academic journal article Teaching Science

Try This: Breaking Stains

Article excerpt

See this activity with full colour pictures: http://www.csiro.au/helix/sciencemail/activities/Starch.html

Warning: This activity uses laundry powder, which can be caustic. Pay attention to the safety directions on the box before using.

YOU WILL NEED

* Flour

* Iodine (from most pharmacies)

* Washing powder with enzymes

* Two jars

* Warm water

* Teaspoon

WHAT TO DO

Measure a teaspoon of flour into two glass jars and add enough warm water to each to turn the flour into a thin paste.

Add a quarter of a teaspoon of washing powder to one of the jars and stir. Allow it to sit for about five minutes and then stir again.

Add one or two drops of iodine to the paste in each jar.

Which one turns a dark blue-black?

WHAT'S HAPPENING?

Flour is essentially wheat that has been ground into a powder. As such, it is mostly made up of what you'd find in grass seeds, which includes glucose that is produced by the plant through the process of photosynthesis and used by the plant for energy. The glucose molecules in plants are linked together in long chains to create a form of energy storage called starch.

To test for the presence of starch in a material, you can drip some iodine onto it and see if it turns blue-black.

On its own, a tincture of iodine is a dark yellow colour. …

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