Using natural dyes in high school courses.

Flowers of Tibouchina granulosa e Bauhinia variegata and skin of black bean grains were used in experiments to identify the acidic or basic character of ordinary materials such as vinegar, fruit juices, detergent formulations, The application was performed with students from public high schools of the city of the Uberlandia - MG - Brazil. The results obtained with the crude extracts was compared with fenolftaleine. Are of the most important point of discussion with the students was the indicator concept. The experiment was performed in the classroom and was very well accepted by the students in the demonstration of acidity; basicity and indicator concepts.