Bromothymol

Bromothymol, commonly referred to as bromothymol blue, is a pH indicator dye used to assess acidity and basicity in aqueous solutions. It belongs to the family of thymol blue indicators and is typically supplied as a water-soluble salt or as a solution suitable for laboratory use.

In solution, bromothymol blue changes color in response to pH. It shifts from yellow in acidic environments to blue in basic ones, with a green to blue transition as pH increases. The effective indicator range is generally cited around pH 6.0 to 7.6, making it especially useful for detecting neutral to mildly basic conditions. The dye is often chosen for applications where a mid-range pH indicator is advantageous, such as monitoring carbonate systems and certain titrations.

Applications of bromothymol blue are widespread in chemistry and biology laboratories. It is commonly used in acid-base titrations, water quality testing (including municipal water and aquaria) to monitor pH and carbonate content, and in environmental analyses where neutral to mildly basic conditions are of interest. It can also serve as a visual indicator in educational demonstrations of pH changes.

Availability and handling: bromothymol blue is sold as an indicator reagent in aqueous or alcoholic solutions and as a solid salt for preparation in solution. It should be stored in a cool, dark place and handled with standard laboratory safety practices. While generally considered low in toxicity, it should be avoided in contact with skin and eyes and inhalation of dust or vapors should be minimized.