Bromothymol blue is a pH indicator that changes color at a specific pH range, typically around pH 6.0 to 7.6. It transitions from yellow at lower pH to blue at higher pH, with green representing the neutral pH of around 7.
If bromothymol blue does not change color during a titration, there could be a few reasons:
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pH Range of the Reaction: The titration might be happening within a pH range where bromothymol blue is not sensitive enough to indicate a color change. For example, if the endpoint of the titration is around pH 7.5 to 8.0, the indicator may be close to its blue form the entire time.
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Concentration of the Indicator: If the concentration of bromothymol blue in the solution is too low, there may not be a visible color change even though there are changes in pH.
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Buffering: The solution being titrated may have buffering components that stabilize the pH in a range that does not allow for a significant change in the color of the indicator.
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Titration Reaction Type: If the titration involves a strong acid being titrated with a strong base or vice versa, the color change may not be evident if the pH transitions are not crossing the pH range that induces a color change for bromothymol blue.
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Temperature: The pH indicator can also be sensitive to temperature, which can affect the pH readings and hence the color change.
If a different color change range indicator is required, other indicators may be more suitable depending on the specific titration being performed.
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