Aqueous solution of `CoCl_(3)*6NH_(3)` upon addition with `AgNO_(3)` produces 3 moles white precipitate . Primary and secondary valency of metal in this complex is

Options

A. 3,6
B. 2,6
C. 3,3
D. 6,4

Answer

To determine the primary and secondary valency of the metal in the complex `CoCl3·6NH3`, we will follow these steps:

### Step 1: Identify the complex and its components
The complex given is `CoCl3·6NH3`. This indicates that cobalt (Co) is the central metal ion, surrounded by three chloride ions (Cl) and six ammonia molecules (NH3).

### Step 2: Determine the reaction with AgNO3
When the complex `CoCl3·6NH3` is treated with silver nitrate (AgNO3), it results in the formation of a white precipitate. The precipitate is silver chloride (AgCl), which forms due to the reaction between the chloride ions and silver ions from AgNO3.

### Step 3: Write the reaction
The reaction can be represented as:
\[ CoCl_3·6NH_3 + 3AgNO_3 \rightarrow Co(NH_3)_6^{3+} + 3AgCl + 3NO_3^{-} \]

Here, three moles of AgCl precipitate out, indicating that there are three chloride ions that are displaced from the complex.

### Step 4: Determine the primary valency
The primary valency corresponds to the oxidation state of the central metal ion (Co) in the complex.

- Let the oxidation state of Co be \(x\).
- The charge contributed by the three chloride ions is \(-3\) (since each Cl has a charge of \(-1\)).
- The ammonia (NH3) is a neutral ligand and contributes \(0\) to the charge.

The overall charge of the complex is \(+3\). Therefore, we can set up the equation:
\[ x - 3 = +3 \]
Solving for \(x\):
\[ x = +6 \]

Thus, the primary valency (oxidation state) of cobalt in this complex is \(+3\).

### Step 5: Determine the secondary valency
The secondary valency refers to the coordination number of the central metal ion, which is determined by the number of ligands attached to it.

- In this complex, there are six ammonia ligands (NH3), each of which has a denticity of 1 (since each NH3 can donate one pair of electrons).
- Therefore, the coordination number is simply the number of ligands:
\[ \text{Coordination number} = 6 \]

Thus, the secondary valency of cobalt in this complex is \(6\).

### Final Answer
- **Primary Valency**: +3
- **Secondary Valency**: 6