Used as a pH indicator in acid-base titrations, particularly for weak acid-strong base reactions. Changes color from red to yellow in acidic range (pH 1.2–2.8) and from yellow to blue in basic range (pH 8.0–9.6). Commonly used in educational labs to demonstrate pH changes and in analytical chemistry for endpoint detection. Also applied in environmental testing to assess the acidity or alkalinity of water samples. Its dual transition range makes it suitable for detecting both strong and weak acid-base reactions.