ACID INDICATOR

MATERIALS

Bromthymol blue (BTB) (available in supply catalogs)
A cup (a glass, or even a test tube)
Drinking straw

PROCEDURE

1. Add 1-2 drops BTB to 15 ml of water.
2. Using the straw, blow into the BTB solution.
3. Observe.

EXPLANATION

BTB is an indicator for acid. Carbon dioxide, when mixed with water, forms a weak acid. When acid is present, the blue BTB will turn yellow. When you blow out, you are blowing out carbon dioxide. You should see the solution turn yellow.
BTB is inexpensive and easily obtained in supply catalogs. You will find that you will use it for more than one experiment.

SAFETY PRECAUTIONS

BTB is a stain and will stain clothing. Always have an adult present and remind children not to put any solutions into their mouths.