The formula of tetraammineaquachloridocobalt(III) chloride is:
- A.[Co(NH₃)₄Cl₂]·H₂O
- B.[Co(NH₃)₄]Cl₃·H₂O
- C.[Co(NH₃)₄(H₂O)Cl]Cl
- D.[Co(NH₃)₄(H₂O)Cl]Cl₂✓
Correct Answer
(D) [Co(NH₃)₄(H₂O)Cl]Cl₂
Solution & Explanation
Build the formula from the IUPAC name, reading the coordination sphere (inside the brackets) first, then the counter-ions. Name parts: tetraammine = 4 NH₃ (neutral), aqua = 1 H₂O (neutral), chlorido = 1 Cl⁻ (inside, −1), cobalt(III) = Co³⁺. The final "chloride" is the counter-ion outside. Charge on the complex ion: +3 (Co) + 0 (NH₃) + 0 (H₂O) + (−1)(coordinated Cl) = +2. So the cation is [Co(NH₃)₄(H₂O)Cl]²⁺, which needs two Cl⁻ outside to balance charge. Complete formula: [Co(NH₃)₄(H₂O)Cl]Cl₂. Trap: only the Cl inside the brackets is a ligand; the two outside are ionisable counter-ions. Answer: option D.
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