Mystery Substances

Any unknown substance found at a crime scene may be important evidence. The liquid left in a drinking glass might be a poison, or the residue found on a suspect’s hand may be gunpowder. As you know, forensic chemist perform many tests on unknown substances in order to identify them. Color, odor, and reaction to other substances are all clues to identify of an unknown substance. Try the following activity to perform another important tes.

Materials
- 1 ½ quarts (1.5 liters) tap water
- 2 quarts (2 liter) saucepan
- 2 red cabbage leaves
- timer
- colander
- plastic bowl
- marking pen
- masking tape
- 5 jar or glasses
- measuring cup
- 3 tablespoons (45 ml) concentrated lemon juice
- 3 tablespoons (45 ml) vinegar
- 3 tablespoons (45 ml) disitilled water
- 1 tablespoons (15 ml) baking soda
- 3 tablespoons (45 ml) ammonia
- pencil
- sheet of white paper
- adult helper

Proceduse
Note: This activity requires adults help.
1. Put the water in the saucepan. Tear the red cabbage leaves into small pieces and place them in the water.
2. Have your adult helper heat the water to boiling and boil the leaves for 5 minutes. Allow the liquid to cool.
3. Hold the colander over the bowl and have your adult helper carefully strain the leaves through the colander. Throw the leaves away.
4. Use the marking pen and masking tape to label jars from 1 to 5.
5. Pour about ½ cup (125 ml) of the cabbage juice into each jar.
6. Add the lemon juice to jar 1, the vinegar to jar 2, the distilled water to jar 3, the baking soda to jar 4, and the ammonia to jar 5.
7. Observe the color that each substance turns the cabbage juice, and record the the color on the chart similar to the one shown.

Caution: Be careful not spill the ammonia on your hands.

Jar Chemical Acid/Basic Colour
1 lemon juice acid
2 vinegar slightly acid
3 distilled water neutral
4 baking soda slightly basic
5 ammonia basic

More Fun Stuff to Do
Use the remaining cabbage juice, ½ cup (125 ml) at a time, to test various household substances. Set up new jars of cabbage juice, add the substances to the juice, and observe the color the juice becomes. Based on the color, use the chart to determine whether the substance is acid, slightly acid, neutral, slightly basic, or basic.

Explanation
There are many tests that forensic scientists perform on unknown substances. A forensic scientist will be first observe the unknown substance, gathering information about its physical characteristics, such as color, texture, Odor, melting point, and boiling point.

Next, the forensic scientist will test the chemical characteristics of the unknown substance. Certain substances are chemicals called acids or bases. Cabbage juice is a chemical indicator that changes color in the presence of an acid or a basie. If the substance tested is acid, the cabbage juice turns red. If the substance is basic, the juice turns green. Listed bellow are the expected results for this activity.

Jar Chemical Acid/Basic Color
1 lemon juice acid red
2 vinegar slightly acid pink
3 distilled water neutral dark purple
4 baking soda slightly basic light green
5 ammonia basic green

Litmus paper is another chemical indicator that can be used to test whether a substance is an acid or a base. You may have used litmus paper in school. The pH scale describes the strength of acid s or bases. Sensitive pH paper or pH meters tell not only whether the unknown substance is acid or basic, but also how strong the acid or basic is.