Question

Which among the following is a correct formula of pentaammine aqua cobalt(III) iodide?

• A. \([\text{Co}(\text{NH}_3)_5(\text{H}_2\text{O})]\text{I}_3\)
• B. \([\text{Co}(\text{H}_2\text{O})(\text{NH}_3)_5\text{I}]\)
• C. \([\text{Co}(\text{NH}_3)_5\text{I}]\text{H}_2\text{O}\)
• D. \([\text{Co}(\text{H}_2\text{O})(\text{NH}_3)_5]\text{I}\)

Hint:

Always check the oxidation state of the metal and the charge of ligands to determine the number of counter ions.

Answer 1

The Correct Option is A

Step 1: Understand the name of the complex.
The complex is pentaammine aqua cobalt(III) iodide. This indicates that cobalt is in the +3 oxidation state and is coordinated with five ammonia molecules and one water molecule.

Step 2: Determine charge on the complex ion.
Ammonia and water are neutral ligands. Cobalt is in the +3 oxidation state, so the complex ion has a charge of \(+3\).

Step 3: Balance with counter ions.
To neutralize the +3 charge, three iodide ions \((\text{I}^-)\) are required outside the coordination sphere.

Step 4: Final structure.
Thus, the correct formula is: \[ [\text{Co}(\text{NH}_3)_5(\text{H}_2\text{O})]\text{I}_3 \]

Step 5: Conclusion.
Option (A) correctly represents the coordination compound.