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Roses, and other flowers and fruits, contain natural indicators that are sensitive to acids and bases. The color of a natural acid–base indicator depends on pH; for example, hydrangea flowers are blue when grown in acidic soils and pink or red in basic soils. With the Natural Indicators: Acids, Bases and the pH Scale—ChemTopic™ Lab Activity, extract natural indicators from flowers and fruits and design a procedure to investigate their color changes as a function of pH with a set of standard acid and base solutions of known pH, then construct color charts of the indicators and analyze the pH values of unknown solutions.