Verification of iron(III) with potassium cyanide

Attention: Inasmuch as the orginally used cyanide was most likely cyanate, false results were obtained. The experiment was repeated with authentic cyanide, and the test procedure, elucidation and photos were corrected. Even if this error fortunately caused no endangerment, still my apologies for this mistake!

Chemicals needed

distilled water

Potassium cyanide solution, diluted   GSGiftig.gif (734 Byte) T+   R 26/27/28-32    S (1-2)-7-28-29-45

Iron(III) chloride solution GSGESUND.gif (476 Byte) Xn    R 22-38-41    S 26-39

Equipment needed

test tube

Test procedure


One adds a surplus of iron(III) chloride solution, in order to complex the cyanide completely. One can then discharge the solution into the drainage and one rinses thoroughly with water.


Iron(III) chloride reacts with potassium cyanide to form the complex potassium hexacyanoferrate(III) (red prussiate of potash) iron-hexacyanoferrate (III) (Prussian blue). One can with this method verify cyanide. Furthermore the formation of this complex is, because of its rather high level of stability, a useful way to render cyanide harmless.

FeCl3 + 6 KCN --> K3[Fe(CN)6] + 3 KCl

2 FeCl3 + 6 KCN --> Fe3[Fe(CN)6] + 6 KCl




of own device