WHAT IS POTASSIUM FERRICYANIDE
Potassium ferricyanide occurs as bright red crystals which are soluble in water. Potassium ferricyanide is manufactured by passing chlorine into a solution of potassium ferrocyanide. It is not considered to be toxic but is dangerous when heated or mixed with other chemicals. It is commonly used in photography and to make dyes, pigments and light sensitive paper.
Properties of Potassium ferricyanide
- Synonyms: Potassium hexacyanoferrate(III); Red prussiate; Prussian red; tripotassium hexacyanoferrate
- Formula: C6N6FeK3 K3Fe(CN)6
- Appearance: red crystals
- Mol weight: 329.24
- Purity: 99+%
- CAS no: 13746–66–2
- EINECS no: 237–323–3
- Density: 1.89
- Melting Point: 300C
- Boiling Point: decomposes
- Solubility: soluble in water 464g/L @20C
- pH: 6–9
It is slowly soluble in 2.5 parts cold water and in 1.3 parts boiling water; slightly soluble in alcohol. It is Stable under normal temperatures and pressures; decomposes on strong heating to evolve highly toxic fumes of hydrogen cyanide gas. Exposure to light can discolour potassium ferricyanide. It is not compatible with many reagents including ammonia, oxidising agents and acids.
Uses for Potassium ferricyanide
Potassium ferricyanide used to prepare Prussian Blue
Potassium ferricyanide is used to prepare Prussian Blue, the deep blue pigment in blue printing. It is produced by the reaction of K3[Fe(CN)6] with ferrous (Fe2+) ions. In medicine prussian blue is used as an antidote for some heavy metal poisoning.
Testing for ferrous ions with potassium ferricyanide
The ability for potassium ferricyanide to be used to test for ferrous ions is beneficial both in medical labs to detect ferrous ions in biological tissue and industrial environments to determine if free metal ions are present on steel or other iron surfaces which lead to rusting.
Potassium ferricyanide for use in photography
Potassium ferricyanide is widely used as a chemical reducer in photographic processing to remove silver from negatives and positives (dot etching). This is done to compensate for minor errors in a photograph or to make deliberate changes in the reproduction. In coluor reproduction of photographs, potassium ferricyanide is used to reduce the size of dots on halftone positives without reducing their density and, thereby, reducing the amount of color in treated areas. This is the most important means of manual colour correction of original color photographs.
Other uses for Potassium ferricyanide
Potassium ferricyanide is also used in tempering iron and steel, sensitive coatings on blueprint paper, wood staining, dyeing wool, production of pigments, electroplating, as a laboratory reagent, and a mild oxidizing agent in organic synthesis. In wine production potassium ferricyanide has been used to precipitate out copper if copper has been used as a fungicide on the grapes.
In the laboratory potassium ferricyanide is used to produce the ferricyanites of heavy metals including mercury, silver, copper, iron 2+ and iron 3+.
Health & safety
R36/38– Irritating to eyes and skin.
S2– Keep out of the reach of children. S46– If swallowed, seek medical advice immediately and show this container or label.
For full fetails see MSDS for Potassium ferricyanide