Identify the formula of pentaaquaisothiocyanatoiron(III) ion from following.

Identify the formula of pentaaquaisothiocyanatoiron(III) ion from following.
  1. $\mathrm{Fe}\left[\left(\mathrm{H}_2 \mathrm{O}\right)_5(\mathrm{SCN})\right]^{3+}$
  2. $\left[\mathrm{Fe}\left(\mathrm{H}_2 \mathrm{O}\right)_5(\mathrm{NCS})\right]^{2+}$
  3. $\mathrm{Fe}\left[\left(\mathrm{H}_2 \mathrm{O}\right)_3(\mathrm{NCS})_2\right]^{3+}$
  4. $\left[\mathrm{Fe}\left[\left(\mathrm{H}_2 \mathrm{O}\right)_2(\mathrm{SCN})_3\right]^{5+}\right.$

Solution

Pentaaqua - This means there are five water molecules, \(\left(\mathrm{H}_2 \mathrm{O}\right)_5\), ligated to the central metal. Isothiocyanato - This refers to the presence of one isothiocyanate ion, represented as (NCS). Iron(III) ion - This indicates that the oxidation state of iron is +3. However, because of ligands and their charges, the net charge on the complex ion should be reconciled. Thus, the stated charge in the problem is a critical clue, as this aligns with the options provided. Option B aligns with these points, providing the correct formula for the pentaaquaisothiocyanatoiron(III) ion.

Asked in: MHT CET 2024 (03 May Shift 1)

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