In the complex ion [Fe(SCN)6]^{3-}, what is the molar ratio of Fe^{3+} ions to [Fe(SCN)6]^{3-} ions?

• A. 1:1
• B. 3:1
• C. 1:6
• D. 6:1

Answer: (A)

Verified step by step guidance

1. Identify the species involved in the complex ion. The complex ion given is \([\text{Fe}(\text{SCN})_6]^{3-}\), which consists of one iron ion and six thiocyanate ions bound together.
2. Understand that the complex ion \([\text{Fe}(\text{SCN})_6]^{3-}\) is a single entity formed by coordination of six \(\text{SCN}^-\) ligands to one \(\text{Fe}^{3+}\) ion.
3. Recognize that the molar ratio refers to the number of moles of \(\text{Fe}^{3+}\) ions relative to the number of moles of the complex ion \([\text{Fe}(\text{SCN})_6]^{3-}\).
4. Since each complex ion contains exactly one \(\text{Fe}^{3+}\) ion, the molar ratio of \(\text{Fe}^{3+}\) ions to \([\text{Fe}(\text{SCN})_6]^{3-}\) ions is 1:1.
5. Therefore, for every mole of \([\text{Fe}(\text{SCN})_6]^{3-}\) complex ions, there is exactly one mole of \(\text{Fe}^{3+}\) ions incorporated within it.