How many EDTA molecules are required to make an octahedral complex with a `Ca^(2+)` ion?

Options

A. six
B. Three
C. One
D. Two

Answer

To determine how many EDTA molecules are required to form an octahedral complex with a \( \text{Ca}^{2+} \) ion, we can follow these steps:

### Step 1: Understand the Structure of EDTA
EDTA (ethylenediaminetetraacetic acid) has a specific structure that allows it to bind to metal ions. It contains two nitrogen atoms and four carboxylate groups, which can donate electron pairs to the metal ion.

### Step 2: Identify the Donor Sites
Each EDTA molecule has six donor sites:
- Two nitrogen atoms
- Four oxygen atoms from the carboxylate groups

This means that EDTA can form multiple bonds with a metal ion.

### Step 3: Determine the Coordination Number of the Metal Ion
In an octahedral complex, the coordination number is typically 6. This means that the metal ion can bond with six ligands or donor atoms.

### Step 4: Relate the Donor Sites to the Coordination Number
Since EDTA is a hexa-dentate ligand, it can bind to a metal ion at all six donor sites. Thus, one EDTA molecule can fulfill the requirement for all six coordination sites in the octahedral complex.

### Step 5: Conclusion
Therefore, only one EDTA molecule is required to form an octahedral complex with a \( \text{Ca}^{2+} \) ion.

### Final Answer
**One EDTA molecule is required.**

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