Many aqueous solutions of complex ions display brilliant colors that depend on the identities of the metal ion and ligand(s). Some ligands bind selectively to certain metal ions, producing complex ions with characteristic colors. These distinctive complex ions serve as qualitative indicators for the presence of particular metal ions. For example, Fe³⁺ is identified by the rapid formation of the intensely colored pentaaquathiocyanatoiron(III) complex ion, [Fe(H₂O)₅SCN]²⁺, when thiocyanate, SCN¯-, is added to a solution containing hexaaquairon(III), [Fe(H₂O)₆]³⁺, according to the following chemical equation:

Examine the absorption spectrum of an aqueous solution of [Fe(H₂O)₅SCN]²⁺ shown here and answer the questions that follow.

Transcribed Image Text:

[Fe(H₂O)]³+ (aq) + SCN¯(aq) — [Fe(H₂O)SCN]²+ (aq) pale violet colorless intensely colored