Suppose You Are Studying Coordination Compounds of Co(II) with the Ligand

question 53

Multiple Choice

Suppose you are studying coordination compounds of Co(II) with the ligand pyridine (py, C₅H₅N, molar mass = 79.10) . You isolate a crystalline compound, and because the only available anions are Cl^- and NO₃^-, you hypothesize that the empirical formula of the coordination compound must be Co_w(py) _x(Cl) _y(NO₃) _z.
-You analyze for pyridine (K_b is approximately 10^-9) by dissolving 0.1000 g of the complex in 100 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) thymol blue, pH range of color change = 8.0-9.6
• B) methyl red, pH range of color change = 4.8-6.0
• C) bromophenol blue, pH range of color change = 3.0-4.6
• D) bromothymol blue, pH range of color change = 6.0-7.6
• E) alizarin yellow, pH range of color change = 10.1-12.0

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