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Step-by-Step Solution
Step 1: Identify the Coordination Complex and Its Ligands
The given complex is [\text{Co}(NH_{3})_{4}Cl_{2}]Cl . In this complex, the cobalt is bonded to four NH_{3} molecules (neutral ligands) and two chloride ions ( Cl^{-} ) as ligands. There is also one chloride ion outside the coordination sphere.
Step 2: Recognize the Nature of Ethylenediamine (en)
Ethylenediamine, commonly abbreviated as en, is a bidentate ligand. This means each en ligand can form two coordinate bonds with the metal center. Its structure is H_{2}N-CH_{2}-CH_{2}-NH_{2} , allowing it to occupy two coordination sites on the cobalt ion.
Step 3: Determine How Many en Ligands Replace the Four NH_{3} Molecules
Since one en ligand takes up two coordination sites (bidentate), it can replace two NH_{3} molecules (each NH_{3} occupies one site). Hence, to replace four NH_{3} molecules, we need two en ligands.
Step 4: Conclude the Required Number of Equivalents of en
Based on the stoichiometry:
[\text{Co}(NH_{3})_{4}Cl_{2}]Cl + 2\,(\text{en}) \rightarrow [\text{Co}(\text{en})_{2}Cl_{2}] + 4\,NH_{3}
Thus, 2 equivalents of ethylenediamine are required to replace the four NH_{3} ligands in the coordination sphere.
Final Answer: 2
