By Kevin Krause, Updated Mar 24, 2022
Bromothymol blue is a widely used pH indicator that shifts from yellow in acidic solutions to blue in basic environments. This step‑by‑step guide shows how to prepare a reliable laboratory-grade solution using common reagents.
Weigh 0.1 g of bromothymol blue powder and dissolve it in 10 mL of a 4 % sodium hydroxide solution in a large beaker. Stir until the powder is fully dispersed.
Introduce 20 mL of isopropyl alcohol to the mixture and continue stirring until the solution becomes clear.
Transfer the mixture to a larger container and dilute with 1 L of distilled water. The resulting solution should display a deep blue hue.
If the color appears green, add sodium hydroxide dropwise with a pipette until the solution turns solid blue. This ensures the solution is fully alkaline.
Sodium hydroxide is caustic; always wear appropriate personal protective equipment, including gloves and eye protection. Prepare the solution in a well‑ventilated laboratory setting using scientific‑grade equipment.
