The ability to accurately measure and control pH is fundamental to countless scientific and industrial processes. Among the array of tools available, pH indicators offer a direct, visual method for assessing acidity and alkalinity. Bromocresol Green (BCG), a widely recognized sulfonephthalein dye, is a prominent example. Its predictable color transitions, governed by specific chemical principles, make it a reliable choice for many applications. As a manufacturer and supplier, understanding the science behind BCG allows us to deliver consistent quality for our clients.

The Chemistry of pH Indication
Bromocresol Green, with CAS number 76-60-8, functions as a weak acid. In aqueous solutions, it exists in equilibrium between its acidic (protonated) form and its basic (deprotonated) form. The specific structure of the dye molecule causes these two forms to absorb and reflect light differently, resulting in distinct colors. The equilibrium shifts based on the hydrogen ion concentration (pH) of the solution.

Bromocresol Green's Specific pH Range
The precise pH range over which Bromocresol Green changes color is critical for its accurate application. This range, known as the transition interval, is typically between pH 3.8 and 5.4. At pH values below 3.8, the acidic form dominates, and the solution appears yellow. As the pH increases and crosses into the transition interval, the dye begins to deprotonate, leading to a mixture of the yellow and blue forms, producing a green color. Above pH 5.4, the basic form predominates, and the solution turns blue. This reliable color change is what makes it so valuable for those who buy pH indicators for quantitative analysis.

Factors Influencing Color Change
While the primary determinant of BCG's color is pH, other factors can subtly influence the observed transition. Temperature, solvent composition, and the presence of other ions or molecules in the solution can slightly alter the indicator's pKa value (the pH at which the acidic and basic forms are present in equal concentrations, approximately 4.90 for BCG). However, for most standard laboratory applications, these effects are minimal, and the indicator provides accurate results. When you buy Bromocresol Green, you are acquiring a tool designed for these typical laboratory conditions.

Applications Driven by Color Change
The predictable color shift of Bromocresol Green is leveraged in several key areas:

• Titrations: It serves as an endpoint indicator in acid-base titrations where the pH falls within its transition range.
• Albumin Assays: Its interaction with albumin, causing a color change, is the basis for quantifying this important blood protein.
• Buffer Verification: It can visually confirm that a buffer solution is functioning within its expected pH range.

Conclusion
The science behind Bromocresol Green's color change is a testament to its utility as a pH indicator. Its well-defined transition range and specific chemical behavior make it an invaluable reagent for a multitude of laboratory tasks. By understanding these principles, scientists can confidently use and procure Bromocresol Green, knowing they are employing a tool designed for accuracy. We are proud to be a supplier of this essential chemical, committed to delivering the quality and predictability that laboratory professionals depend on.