Suppose you are studying coordination compounds of Co(II) with the ligand pyridine (py, C5H5N, MW = 79.10). You isolate a crystalline compound and since the only available ions are chloride and nitrate, you hypothesize the empirical formula of the coordinaton compound must be Co(II)w(py)x(Cl)y(NO3)z. You analyze for pyridine (Kb is approximately 10-9) by dissolving 0.1000 g of complex in 10 mL of water and titrating with a 0.01 M HCl solution. Which of the following indicators sould be used to detect the endpoint? (Assume that the initial concentration of pyridine is approximately 0.01 M.)

Question

Suppose you are studying coordination compounds of Co(II) with the ligand pyridine (py, C5H5N, MW = 79.10). You isolate a crystalline compound and since the only available ions are chloride and nitrate, you hypothesize the empirical formula of the coordinaton compound must be Co(II)w(py)x(Cl)y(NO3)z. You analyze for pyridine (Kb is approximately 10-9) by dissolving 0.1000 g of complex in 10 mL of water and titrating with a 0.01 M HCl solution. Which of the following indicators sould be used to detect the endpoint? (Assume that the initial concentration of pyridine is approximately 0.01 M.) 
-bromophenol blue (pH range of color change: 3.0 -4.6) 
-thymolblue (pH range of color change: 8.0 - 9.6) 
-bromothymol blue (pH range of color change: 6.0 - 7.6) 
-alizarin yellow (pH range of color change: 10.1-12.0) 
-methyl red (pH range of color change: 4.8 - 6.0)

This is a base which reacts with HCl to form the salt of the base. Base + H^+ ==> BH^+.

At the equivalence point, we will have just the salt and water present. So the pH will be determined by the hydrolysis of the salt. 
BH^+ + HOH ==> B + H3O^+

(Kw/Kb) = (B)(H3O^+)/(BH^+) 
and since (B)=(H3O^+), then 
(H3O+)^2 = [Kw(BH^+)]/Kb). 
You know Kw, Kb, and (BH^+) = 0.01. 
Solve for H^+ and match that with te appropriate pH range.

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Suppose you are studying coordination compounds of Co(II) with the ligand pyridine (py, C5H5N, MW = 79.10). You isolate a crystalline compound and since the only available ions are chloride and nitrate, you hypothesize the empirical formula of the coordinaton compound must be Co(II)w(py)x(Cl)y(NO3)z. you discover that the complex decomposes in water. you dissolve 0.1000g of the complex in water and add excess NaHg(SSN)4. after the precipitate washed and dried its mass is 0.1102g. how many grams of cobalt are contained in the 0.1000g of the complex?