Final answer:
Bromophenol blue changes from yellow to blue due to a chemical reaction happening when the pH of the solution is altered.
Step-by-step explanation:
The color change from yellow to blue in bromophenol solutions is due to a chemical reaction. Bromophenol blue is an indicator that undergoes a color change depending on the pH of the solution it is in. In acidic conditions, the bromophenol solution appears yellow, while in basic conditions, it turns blue.
This color change occurs because the bromophenol blue molecule has different forms, or species, depending on the pH. In an acidic solution, the molecule is in its yellow form, which absorbs light in the visible spectrum and gives the solution its yellow color. In a basic solution, the molecule converts to its blue form, which also absorbs light in the visible spectrum but at a different wavelength, resulting in a blue color.