Thiocyanate complex formation. 0.5 M solution of potassium thiocyanate (KSCN) is added drop by drop to a test tube with 0.25 M solution of iron(III) chloride. Iron chloride solution has a yellow color due to formation of hexaaquairon(III) complex ion ([Fe(H2O)6]3+). When potassium thiocyanate (KSCN) is added, iron(III) ion (Fe3+) complexes with thiocyanate ion ([SCN]-), producing thiocyanatoiron(III) complex ion ([Fe(SCN)]2+) that gives the solution its blood red color. This reaction can be used as a test for Fe3+ ions in a solution.