You analyze for pyridine (Kb is approximately 10^-9) by dissolving 0.1000 g of the complex in 10 mL of H2O and titrating with a 0.01 M HCl solution. Which of the following indicators should be used to detect the endpoint? (Assume that the initial concentration of pyridine is approximately 0.01 M.)
A) bromophenol blue, pH range of color change = 3.0-4.6
B) methyl red, pH range of color change = 4.8-6.0 C) bromothymol blue, pH range of color change = 6.0-7.6
D) thymol blue, pH range of color change = 8.0-9.6
E) alizarin yellow, pH range of color change = 10.1-12.0
The answer is A.
I think the answer should be B since pyridine is a weak base, as it is titrated by strong acid its endpoint should be slightly acidic. However, option A is much more acidic than B, why?