Numerical answer · +4 / −1
In [Co(NH₃)₆]Cl₃, the oxidation state of Co is x.
Answer and solution
Answer 3
Solution
Chemistry ma’am · 3 steps
Three chlorides outside the bracket tell you the charge on the complex ion; ammonia adds nothing.
- Split the formula. The square bracket holds the complex ion. The three Cl⁻ ions sit outside as counter ions, so the complex ion must carry a charge of +3 to balance them: [Co(NH₃)₆]³⁺.
- Ligand charges. Each NH₃ is a neutral ligand, so the six of them contribute zero charge.
x + 6(0) = +3
- So. x = +3. Cobalt is in the +3 oxidation state, so the answer is 3.
The common slip: 9. Treating each NH₃ as -1, like a chloride, gives x - 6 = +3, that is 9, which is not a possible state for cobalt.
The idea to keep. Read the counter ions first to get the charge on the complex ion, then subtract the ligand charges. Neutral ligands like NH₃, H₂O and CO contribute zero.
Answer from the NTA final answer key. Solution by PrepWiser.