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

To determine the correct structure of the complex compound \( \text{Co(NH}_3)_5\text{Cl}_3 \), we must consider the given information about its behavior in water and its reaction with excess \( \text{AgNO}_3 \) solution: 

1. When one mole of the complex dissolves in water, it gives three moles of ions.
2. One mole of the complex reacts with an excess of \( \text{AgNO}_3 \) to yield two moles of \( \text{AgCl} \).

Let's evaluate each structural option against these criteria:

1. Option 1: \([ \text{Co(NH}_3)_5\text{Cl}] \text{Cl}_2\)

This complex will dissociate in water as follows:

\([ \text{Co(NH}_3)_5\text{Cl}]^{2+} + 2\text{Cl}^- \rightarrow 3 \text{ ions}\)

When reacting with excess \( \text{AgNO}_3 \), both chloride ions precipitate as \( \text{AgCl} \):

\(2\text{Cl}^- + 2\text{Ag}^+ \rightarrow 2\text{AgCl} \)

Thus, Option 1 meets both criteria: it forms three ions upon dissociation and produces two moles of \( \text{AgCl} \) when treated with \( \text{AgNO}_3 \).

1. Option 2: \([ \text{Co(NH}_3)_4\text{Cl} ] \cdot \text{Cl}_2\text{NH}_3\)

This option doesn't align with the given conditions as it suggests extra coordinated water/ammonia molecules, which complicates the dissociation behavior beyond the specified 3 ions.

1. Option 3: \([ \text{Co(NH}_3)_4\text{Cl}_2 ]\text{Cl} \cdot \text{NH}_3\)

This structure suggests that there are two coordination chlorides, which would lead to a different reaction behavior with \( \text{AgNO}_3 \) making the formation of two moles of \( \text{AgCl} \) less feasible.

1. Option 4: \([ \text{Co(NH}_3)_3\text{Cl} ] \cdot \text{Cl}_3 \cdot 2\text{NH}_3\)

This option suggests an incorrect stoichiometry yielding more ions that do not fit the given conditions.

Hence, the correct structure of the complex based on the given information is:

\([Co(NH_3)_5Cl]Cl_2\).

Answer 2

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 \( \boxed{[{Co(NH}_3{)}_5{Cl}]{Cl}_2} \).