Mystery Powders

White powder found at a crime scene or in a suspect's pocket may be an illegal substance or merely sugar. A detective will have a crime lab identify the substance to determine whether a crime has been committed. Try the following activity to learn how forensic chemists use chemistry to identify unknown substances.

Materials
- Pencil
- Sheet of white paper
- measuring spoon set
- baking soda
- sugar
- salt
- cornstarch
- 4 sheets of black construction paper
- white chalk
- magnifying lens
- eyedropper
- water
- 4 small jars
- iodine solution (available at most drugstores)
- dish towel
- vinegar

Procedure
1. Use the pencil and white paper to create a chart similar to the one shown bellow.
2. Put 1/4 teaspoon (1 ml) of each white powder (baking soda, sugar, salt, and cornstarch) on a separate sheet of black construction paper. Use the chalk to label each powder.
3. Examine each powder with the magnifying lens. What does each powder look like? What its shape? Are its grains large or small? Record your observations in the appearance column of the chart.
4. Rub each powder between your fingers. How does it feel? Record your comments in the Texture column.
5. Do any of the powders have a smell? If so, record that information in the Smell column.
6. Use the eyedropper to place a drop af water on each powder. What happens? Do any of the powders dissolve or react in any other way? Record the results in the Reaction to Water column.
7. Put ½ teaspoon (2 ml) of each powder in a separate jar. Use the eye dropper to add 2 drops of iodine solution to each jar. Observer what happens and record your observations in the Reaction to Iodine column.
8. Rinse and dry the jars.
9. Put ½ teaspoon (2 ml) of each powder in a separate jar. Use the eye dropper to add 2 drops of vinegar solution to each jar. Observer what happens and record your observations in the Reaction to Vinegar column.

Appearance:Texture:Smell:Reaction to Water:Reaction to Iodine:Reaction to Vinegar
Baking Soda:
Sugar:
Salt:
Cornstarch:


More Fun Stuff to Do
Can you identify a mystery powder? Have a helper give you a small amount of one of the white powders without telling you which one it is. Repeat the chemical tests on the mystery powder and compare your results to those on the chart to identify the powder. Check with your helper to see whether you were correct.

Explanation
The results of your tests in this activity should be similar to those listed in the chart bellow.
If you did the More Fun Stuff to Do Activity, you should have been able to identify the unknown substance by repeating the tests and comparing your results to the results listed in your chart.
Just as you did in this activity, forensic scientists use a variety of tests to identify an unknown substance. Some tests examine the physical characteristics of a substance, such as its color, shape, and so forth. Other tests explore how it reacts to an acid, and so on. Forensic scientists compare the results of tests done on unknown substances to the results of tests done on known substances to identify the unknown substances.