Bromothymol blue

Bromothymol Blue is a pH indicator and dye that is primarily used in laboratories. It is a member of the thymol blue family and is derived from thymol. Bromothymol blue is also known as BTB, Bromthymol Blue, and Bromothymol Sulfone Phthalein.

Chemical Properties

Bromothymol blue is a weak acid. It is most accurate in the pH range 6.0–7.6. It changes color over this pH range from yellow (acidic) to blue (basic). The transition from the acid to the base happens around neutral pH 6.0–7.6, which is the pH of most living cells.

Uses

Bromothymol blue is commonly used in scientific research to identify whether a solution is acidic or basic. It is also used in medicine to measure the presence of carbon dioxide in exhaled air, indicating whether a person's lungs are functioning properly.

Preparation

Bromothymol blue can be prepared by brominating thymol blue in a solution of acetic acid and acetic anhydride, in the presence of phosphorus tribromide.

Safety

Bromothymol blue is considered a safe substance for laboratory use, but it can be harmful if ingested or inhaled, and it can cause irritation if it comes into contact with the skin or eyes.

See Also

• pH indicator
• Acid-base titration
• Thymol blue