In the Lassaigne's test, when both nitrogen and sulphur are present, a blood-red colored complex is — Practical Organic Chemistry and Purification Chemistry Question
Question
In the Lassaigne's test, when both nitrogen and sulphur are present, a blood-red colored complex $Fe(SCN)_3$ is formed upon addition of ferric ions. What is the formal oxidation state of the central iron ($Fe$) atom in this complex?
Answer: 3
💡 Solution & Explanation
The thiocyanate ligand ($SCN^-$) carries a charge of $-1$. In the neutral complex $Fe(SCN)_3$, or the similarly formed $[Fe(SCN)]^{2+}$ ion in solution, the formal oxidation state of the iron atom is $+3$.
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