Phenolphthalein and bromothymol blue are used for what?

Phenolphthalein and bromothymol blue are used for what?

• A. Solvents
• B. Reactants in polymerization
• C. Indicators used to indicate acidity or basicity
• D. Catalysts

Answer: (C)

pH indicators. These compounds change color as the hydrogen ion concentration of a solution changes, giving a visible signal of whether the solution is acidic or basic. Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions (transition around pH 8.2–10), while bromothymol blue shifts from yellow in acidic conditions to blue in basic conditions (transition near pH 6–7.6). This color change makes them useful in monitoring acidity or basicity, especially in acid–base titrations. They are not solvents, polymerization reagents, or catalysts—their role is to indicate pH through color.

pH indicators. These compounds change color as the hydrogen ion concentration of a solution changes, giving a visible signal of whether the solution is acidic or basic. Phenolphthalein is colorless in acidic solutions and turns pink in basic solutions (transition around pH 8.2–10), while bromothymol blue shifts from yellow in acidic conditions to blue in basic conditions (transition near pH 6–7.6). This color change makes them useful in monitoring acidity or basicity, especially in acid–base titrations. They are not solvents, polymerization reagents, or catalysts—their role is to indicate pH through color.