Sharon Endebak

Mystery Powders

Science Concept:

Using our sense of sight, we will prove what each powder is by adding a chemical substance to each of them.

Materials:

four - 100 mL beakers

four - 250 mL beakers

flour

sugar

baking soda

vinegar

iodine solution

Directions:

1. Measure about 3-4 spatula spoons of each powder, and put into each beaker ( three - 100 mL beakers and three - 250 mL beakers.). Choose one of the powders to be the "unknown" and put it into each of the fourth beakers.

2. Add about 1-2 mL of iodine solution to the powders in the 100 mL beakers.

3. Add about 1-2 mL of vinegar to each of the powders in the 250 mL beakers.

Introduction:

Today I am a detective helping out the police on the scene of a crime. Each suspects house was searched.The police have found a white powder that could be sugar, baking soda, or flour. Joe had an open bag of sugar in house, Mike had an open bag of flour, and Mary had an open box of baking soda. Who did it???

The white powde at the crime scene needs to be taken to a lab to be tested. We cannot taste the powders because we don't know what might be in them. So first we will take known samples of each powder and test them with iodine and starch. Finally we perform the same tests on the unknown sample.

Explanation:

The starch in the flour is like a polymer chain that is a coil-like spring. When the liquid iodine is added, it goes inside this coil and turns the flour black. Neither the baking soda nor the sugar has starch so these powders do not change color, but give the original orange/brown color of the iodine. The vinegar is an acid that only reacts with carbonate ions such as iin the baking soda. When they react, they form bubbles of carbon dioxide. The flour and sugar do not make bubbles. With these reactions, we can determine which powder is which.

Safety:

Use caution using the iodine solution. It is not a harmful chemical; however, it will stain clothes and skin. Otherwise, all of the powders and the vinegar are harmless.

Disposal:

All of these reactions can be disposed of in the sink.

Reference: Unknown