They are useful to the biologist because they produce characteristic color changes at various degrees of acidity or basicity. Most indicators are organic dyes with complex formulas that are synthesized in laboratories using reactions that are also complicated.
Litmus paper is an example of an acid-base indicator commonly used in the middle school laboratory.
Some indicators, however, can be derived from easily obtainable plants. In this activity you will extract one to these natural acid-base indicators and use it to find the approximate pH values of some substances you might find at home or at school. Some of the household chemicals used here are caustic and can be very dangerous when mixed. Wear safety goggles and disposable gloves. Be very careful when handling these chemicals and when disposing of them.