Question

One mole of the octahedral complex compound \( \text{Co(NH}_3)_5\text{Cl}_3 \) gives 3 moles of ions on dissolution in water. One mole of the same complex reacts with excess of \( \text{AgNO}_3 \) solution to yield two moles of \( \text{AgCl}(s) \). The structure of the complex is:

• A. \( [{Co(NH}_3{)}_5{Cl}]{Cl}_2 \)
• B. \( [{Co(NH}_3{)}_4{Cl}]\cdot {Cl}_2{NH}_3 \)
• C. \( [{Co(NH}_3{)}_4{Cl}_2]{Cl}\cdot {NH}_3 \)
• D. \( [{Co(NH}_3{)}_3{Cl}]\cdot {Cl}_3\cdot 2{NH}_3 \)

Hint:

The number of free ions in a complex can be determined by how they interact with reagents like \( {AgNO}_3 \). In this case, the number of chloride ions reacting with \( {AgNO}_3 \) determines which chloride ions are free.

Answer 1

The Correct Option is A

The complex compound \( {Co(NH}_3{)}_5{Cl}_3 \) dissociates in water into: \[ {[Co(NH}_3{)}_5{Cl}]^{3+} \quad {and} \quad 3 \, {Cl}^- \] This gives 3 moles of ions for 1 mole of the complex. When the complex reacts with excess \( {AgNO}_3 \), two moles of \( {AgCl}(s) \) are formed, indicating that 2 chloride ions are free to react. This implies that the structure of the complex is: \[ [{Co(NH}_3{)}_5{Cl}]{Cl}_2 \] where one chloride ion is part of the coordination sphere and the other two chloride ions are free to react with \( {AgNO}_3 \). 
Thus, the correct structure of the complex is \( \boxed{[{Co(NH}_3{)}_5{Cl}]{Cl}_2} \).