Which indicator is best suited to determine the equivalence point of a titration of diethlyamine with HBr?
pKb of diethylamine=3.16
A) phenolpthalein pKHIN ~9
B) bromo blue pKHIN ~4
C) alizarin yellow pKHIN~11
D) methyl violet pKHIN~ 1
E) phenol red pKHIN ~ 7.5
?
Phenolpthaline
To determine the equivalence point of a titration, we need to choose an indicator that changes color at a pH value close to the expected pH of the equivalence point.
In this case, we are titrating diethylamine (a weak base) with HBr (a strong acid). The equivalence point of this titration is when the moles of diethylamine and HBr are in a 1:1 ratio, resulting in a neutral solution. Since HBr is a strong acid, the pH at the equivalence point will be very low (acidic).
Now, let's analyze the options:
A) phenolphthalein pKHIN ~9
Phenolphthalein changes color around pH 9-10, which is too high for the equivalence point of this titration. It is not suitable for determining the equivalence point.
B) bromo blue pKHIN ~4
Bromo blue changes color around pH 3-4, which is closer to the expected pH of the equivalence point. It is a better option than phenolphthalein but may not be the best choice for high accuracy.
C) alizarin yellow pKHIN ~11
Alizarin yellow changes color around pH 10-11, which is too high for the equivalence point of this titration. It is not suitable for determining the equivalence point.
D) methyl violet pKHIN ~ 1
Methyl violet changes color around pH 0-1, which is far from the expected pH of the equivalence point. It is not suitable for determining the equivalence point.
E) phenol red pKHIN ~ 7.5
Phenol red changes color around pH 6.8-8.4, which is closer to the expected pH of the equivalence point. It is a reasonably good option, but there might be a better indicator with a closer pH range.
Based on the given indicator options, the best choice for determining the equivalence point of the diethylamine and HBr titration is phenol red (Option E) because it has a pH range that is reasonably close to the expected pH of the equivalence point. However, for higher accuracy, it is always recommended to consult a reference or conduct preliminary experiments to determine the best indicator for a specific titration.