Aqueous reaction solution and method of passivating workpieces having zinc or zinc alloy surfaces and use of a heteroaromatic compound

An aqueous reaction solution for passivating workpieces having zinc or zinc alloy surfaces, containing trivalent chromium ions, at least one acid, and at least one heteroaromatic compound selected from the group consisting of nicotinic acid, the salts and derivatives thereof, wherein the concentration of the trivalent chromium ions is from about 0.2 to about 30 g/l, wherein the concentration of the at least one heteroaromatic compound is in a range from about 4·10−3 Mol/L to about 325·10−3 Mol/L, and wherein the aqueous reaction solution forms a passivation layer on the workpieces based on Cr(III).