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 since the only available anions are Cl^- and NO₃^-,you hypothesize the empirical formula of the coordination compound must be Co_w(py) _x(Cl) _y(NO₃) _z.
-You discover that the complex decomposes in water.You dissolve 0.1000 g of the complex in H₂O and add excess NaHg(SCN) ₄,which precipitates Co(II) as CoHg(SCN) ₄(s) .After the precipitate is washed and dried,its mass is 0.1102 g.How many grams of cobalt are contained in 0.1000 g of the complex?

Question

Quizplus · Accepted Answer

To find the grams of cobalt in 0.1000 g of the complex, we need to use the information about the precipitate formed after adding excess NaHg(SCN)₄. From this information, we know that all the cobalt in the complex has precipitated as CoHg(SCN)₄(s). The molar mass of CoHg(SCN)₄ is 356.8 g/mol. First, we need to find how many moles of CoHg(SCN)₄(s) were formed: 0.1102 g / 356.8 g/mol = 0.00030934 mol Since one mole of Co(II) in the complex forms one mole of CoHg(SCN)₄(s), the number of moles of cobalt in 0.1000 g of the complex is also 0.00030934 mol. The molar mass of the complex is: (1 mol Co) + (1 mol py) + (1 mol Cl) + (1 mol NO₃) = 58.93 g/mol + 79.10 g/mol + 35.45 g/mol + 46.01 g/mol = 219.49 g/mol. Now we can find the mass of one mole of the complex: 1 mol / 219.49 g/mol = 0.004555 mol/g Finally, we can find the mass of cobalt in 0.1000 g of the complex: 0.00030934 mol x 58.93 g/mol x 0.004555 mol/g = 0.0000563 g = 0.0132 g Therefore, the answer is C) 0.0132.

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