Question

Cobalt chloride, when dissolved in water, forms a pink-colored solution. Identify the reason.

• A. The formation of \([\text{Co(H}_{2}\text{O)}_{6}]^{2+}\) complex that has octahedral geometry.
• B. The formation of \([\text{Co(H}_{2}\text{O)}_{6}]^{2+}\) complex that has tetrahedral geometry.
• C. The formation of \([\text{Co(H}_{2}\text{O)}_{6}]^{2-}\) complex that has tetrahedral geometry.
• D. The formation of \([\text{Co(H}_{3}\text{O)}_{6}]^{2+}\) complex that has octahedral geometry.

Hint:

Cobalt(II) ions bind six water molecules in water to form an octahedral aqua complex.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
When cobalt chloride dissolves in water, the \(\text{Co}^{2+}\) ion gets surrounded by water ligands.

Step 2: Formula of the complex
Six water molecules bind to give \([\text{Co(H}_2\text{O)}_6]^{2+}\) with octahedral geometry.

Step 3: Colour
The d-d transitions in this octahedral aqua complex absorb light so the solution appears pink. The tetrahedral chloro complex is blue.

Final Answer:
The pink colour is due to the octahedral hexaaquacobalt(II) ion. \[ \boxed{\text{(A) }\text{The formation of }[\text{Co(H}_{2}\text{O)}_{6}]^{2+}\text{ with octahedral geometry}} \]