Out of the following complex compounds, which compound will have the minimum conductance in solution?

Solution & Explanation

\textbf{Answer:} (C) \ce{[Co(NH3)3Cl3]}. \textbf{Solution:} Molar conductance depends on the number of ions a complex releases in solution. Only chloride ions outside the coordination sphere ionise; those bonded to the metal do not. \ce{[Co(NH3)6]Cl3} $\rightarrow$ 1 cation + 3 \ce{Cl-} = 4 ions (highest conductance). \ce{[Co(NH3)5Cl]Cl2} $\rightarrow$ 1 cation + 2 \ce{Cl-} = 3 ions. \ce{[Co(NH3)4Cl2]Cl} $\rightarrow$ 1 cation + 1 \ce{Cl-} = 2 ions. \ce{[Co(NH3)3Cl3]} $\rightarrow$ all three \ce{Cl-} are inside the sphere, giving a neutral non-electrolyte with 0 ions. With no ions in solution, \ce{[Co(NH3)3Cl3]} has the \textbf{minimum conductance}, option (C). Note: the source key lists (d); however as written here \ce{[Co(NH3)4Cl2]Cl} ionises into 2 ions, so the fully neutral non-electrolyte \ce{[Co(NH3)3Cl3]} (Werner's classic) is the chemically correct minimum-conductance answer, (C).