What is the coordination number of the metal ion in the red complex ion formed in a quanlitative analysis test of iron(III)?

Explanation

To determine the coordination number of the metal ion in the red complex ion formed during the qualitative analysis test of iron(III), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Metal Ion**: The metal ion in question is iron(III), denoted as Fe³⁺.

2. **Understand the Reaction**: In the qualitative analysis test, iron(III) ions react with thiocyanate ions (SCN⁻) to form a complex. The reaction can be represented as:
\[ \text{Fe}^{3+} + 6 \text{H}_2\text{O} \rightarrow \text{[Fe(H}_2\text{O)}_6]^{3+} \]
This indicates that iron(III) is initially coordinated with six water molecules.

3. **Formation of the Red Complex**: When thiocyanate ions are added, the reaction proceeds as follows:
\[ \text{[Fe(H}_2\text{O)}_6]^{3+} + \text{SCN}^- \rightarrow \text{[Fe(H}_2\text{O)}_5\text{SCN}]^{2+} + \text{H}_2\text{O} \]
Here, one of the water molecules is replaced by a thiocyanate ion.

4. **Count the Ligands**: In the resulting complex \(\text{[Fe(H}_2\text{O)}_5\text{SCN}]^{2+}\), there are a total of six ligands attached to the iron ion:
- 5 water molecules (H₂O)
- 1 thiocyanate ion (SCN⁻)

5. **Determine the Coordination Number**: The coordination number is defined as the total number of ligands attached to the central metal ion. In this case, the coordination number of Fe³⁺ in the red complex is:
\[ \text{Coordination Number} = 5 \text{ (from H}_2\text{O)} + 1 \text{ (from SCN)} = 6 \]

6. **Conclusion**: Therefore, the coordination number of the metal ion in the red complex ion formed during the qualitative analysis test of iron(III) is 6.

### Final Answer:
The coordination number of the metal ion in the red complex ion formed in a qualitative analysis test of iron(III) is **6**.

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