Difference between revisions of "Prussian blue"
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3FeCl<sub>2</sub> + FeCl<sub>3</sub> + 3K<sub>3</sub>[Fe(CN)<sub>6</sub>] → Fe<sub>4</sub>[Fe(CN)<sub>6</sub>]<sub>3</sub>↓ + 9KCl | 3FeCl<sub>2</sub> + FeCl<sub>3</sub> + 3K<sub>3</sub>[Fe(CN)<sub>6</sub>] → Fe<sub>4</sub>[Fe(CN)<sub>6</sub>]<sub>3</sub>↓ + 9KCl | ||
| − | These reactions can be used to detect the presence of iron. Use potassium | + | These reactions can be used to detect the presence of iron. Use potassium ferrocyanide to detect trivalent iron, and ferricyanide to detect divalent iron. |
== Projects == | == Projects == | ||
Revision as of 21:16, 14 August 2015
Prussian blue is a complex salt of iron and hexacyanoferric acids, or a double salt of iron and potassium thereof. This compound comes in several forms, though they all are similar. It doesn't have a definite formula or IUPAC name, because it is in fact several closely related compounds usually encountered together. It is used as a pigment.
Contents
Properties
Physical
Prussian blue is a powder that can be light or dark blue (the dark variety is called Turnbull's blue). It is insoluble in water, but it is possible to prepare a colloidal solution of Prussian blue. The double salt with potassium produces colloidal solutions easily, hence it is known as "soluble Prussian blue", though it isn't truly soluble.
Chemical
Prussian blue is relatively inert under normal conditions. However, if heated to 200 degrees Celsius, it will decompose and liberate cyanogen gas (dangerous!). Stronger heating causes the cyanides themselves to decompose, nitrogen is liberated, leaving iron carbide and carbon in the test tube.
Availability
It is still commonly used as a pigment and can be bought in art stores.
Preparation
We will list several reactions that can be used to prepare Prussian blue of different types. They are notable in that they are used to detect ions of iron, not to specifically prepare the blue pigment.
"Standard", light blue Prussian blue can be precipitated with the following reaction:
4FeCl3 + 3K4[Fe(CN)6] → Fe4[Fe(CN)6]3↓ + 12KCl
The "soluble" kind of Prussian blue can be prepared this way:
FeCl3 + K4[Fe(CN)6] → KFe[Fe(CN)6]3↓ + 3KCl
The dark blue variety called Turnbull's blue is prepared this way:
3FeCl2 + FeCl3 + 3K3[Fe(CN)6] → Fe4[Fe(CN)6]3↓ + 9KCl
These reactions can be used to detect the presence of iron. Use potassium ferrocyanide to detect trivalent iron, and ferricyanide to detect divalent iron.
Projects
- Make cyanogen gas
Handling
Safety
All varieties of Prussian blue are safe under normal conditions.
Storage
Prussian blue can be kept in any jar.
Disposal
Prussian blue can be discarded with common garbage.
