Bromocresol green is a pH indicator that typically transitions from blue to yellow over a specific pH range (approximately pH 3.8 to 5.4). In a titration, the observed color change can depend on the nature of the titration and the pH changes that occur during the process.
-
In Acidic Solutions: In acidic environments (pH < 3.8), bromocresol green is yellow. As the pH increases and moves toward neutral (around pH 4.6), the solution transitions to green, and eventually to blue if the pH exceeds about 5.4.
-
In Basic Solutions: If the environment becomes too basic (pH > 5.4), bromocresol green can appear blue, especially in a strongly basic solution.
Thus, if you are observing bromocresol green turning from blue to colorless during a titration, it is likely because you are moving below its transition pH range due to the addition of a strong acid (like HCl). As the titration progresses and the pH decreases into the acidic range, the blue color would fade and eventually you would see a more yellow or colorless solution, depending on the exact pH reached.
In summary, the color change from blue to colorless (or yellow) indicates a decrease in pH due to the addition of an acid during the titration.
1 answer