JAMB Chemistry 2024 Paper

Concept:In coordination nomenclature, name the cation first, then the complex anion, and state the metal's oxidation number in Roman numerals in parentheses.Explanation:The compound $K_4[\mathrm{Fe}(\mathrm{CN})_6]$ gives $4\mathrm{K}^+$ ions and the complex ion $[\mathrm{Fe}(\mathrm{CN})_6]^{4-}$.Each cyanide ligand, $\mathrm{CN}^-$, carries a charge of $-1$.Thus, six cyanide ligands contribute a total charge of $-6$.Let the oxidation state of Fe be $x$.The total charge on the complex ion is $-4$, so $x + (-6) = -4$.Solving gives $x = +2$.Because the complex is an anion, the metal is named as “ferrate”.Six cyanide groups are named as “hexacyano”.Therefore, the name is potassium hexacyanoferrate(II).Answer:A. potassium hexacyanoferrate(II)