Addition of an aqueous solution of Fe(II) to potassium hexacyanochromate (III) produces a brick-red colured… · ABC26IN0679

Subject: Inorganic Chemistry · Chapter: d-Block Elements · Topic: D Block – General · Exam: JAM 2005-2022 · Marks: 2 · Difficulty: Medium

Addition of an aqueous solution of Fe(II) to potassium hexacyanochromate (III) produces a brick-red colured complex, which turns dark green at $100^{\circ} \mathrm{C}$. The dark green complex is

(a)$\mathrm{Fe}_{4}\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]_{3}$

(b)$\mathrm{KFe}\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]$

(d)$\mathrm{Fe}\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]$

(c)$\mathrm{KCr}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$

Answer

Answer: C ✓ checked by 4AB · confidence high

Explanation

The brick-red KFe(II)[Cr(CN)₆] isomerises on heating (CN⁻ flips to C-bound Fe) to dark-green KCr[Fe(CN)₆] (c).

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