Question

why is bromocresol green turns blue to colorless in a titration

Answer 1

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.

1. **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.

2. **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.