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GATE 2022 CY – Question 47

Inorganic Chemistry · Instrumental Methods of Analysis: UV-visible, fluorescence and FT-IR spectrophotometry, NMR and ESR spectroscopy, mass spectrometry, atomic absorption spectroscopy, Mössbauer spectroscopy (Fe and Sn) and X- ray crystallography. Electroanalytical methods – cyclic voltammetry, ion-selective electrodes. Thermo-analytical methods: TGA, DTA and DSC. · 2 marks · Multiple choice

The addition of K4[Fe(CN)6] to a neutral aqueous solution of the cationic species of a metal produces a brown precipitate that is insoluble in dilute acid. The cationic species is

  1. $Fe^{3+}$
  2. $UO_2^{2+}$
  3. $Th^{4+}$
  4. $Cu^{2+}$

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Correct answer: (D) $Cu^{2+}$

Explanation

Copper(II) reacts with[Fe(CN)6]4− toproduce brown copper(II) ferrocyanide, Cu2[Fe(CN)6], insoluble in dilute acid. Fe(III) instead gives Prussian blue.

Thus the observed colour and solubility select **Cu2+, D**.