Sodium ferrioxalate

Sodium ferrioxalate is a chemical compound with the formula Na
3Fe(C
2O
4)
3. It is also called sodium oxalatoferrate or sodium trisoxalatoferrate.

Sodium ferrioxalate
Names
IUPAC name
Sodium iron(III) oxalate
Other names
Sodium ferrioxalate

Sodium ferric oxalate
Sodium trisoxalatoferrate (III)

Sodium oxalatoferrate
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 209-092-9
Properties
C6FeNa3O12
Molar mass 388.868 g·mol−1
Density 1.97 g/cm3 at 17 °C
32.5pts per 100pts solvent, cold water, 182pts per 100pts, boiling water[1]
Structure
octahedral
0 D
Hazards
Main hazards Corrosive. Eye, respiratory and skin irritant.
GHS pictograms
GHS Signal word Warning
H302, H312
P264, P270, P280, P301+312, P302+352, P312, P322, P330, P363, P501
Related compounds
Other anions
 Potassium ferrioxalate
Related compounds
 Iron(II) oxalate
Iron(III) oxalate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

The compound is a salt consisting of ferrioxalate anions, [Fe(C
2O
4)
3]3−, and sodium cations Na+. The anion is a transition metal complex consisting of an iron atom in the +3 oxidation state and three bidentate oxalate ions C
2O2−
4 anions acting as ligands.

The ferrioxalate anion is sensitive to light and higher-energy electromagnetic radiation, which causes the decomposition of one oxalate to carbon dioxide CO
2 and reduction of the iron(III) atom to iron(II).

Properties

Solubility

This compound is very soluble in hot water, (182 parts per 100 parts solvent by mass), but a lot less soluble in cold water, (32 parts per 100 parts solvent), about the solubility of sodium chloride. It is not appreciably soluble in ethanol or ethanol water mixtures which are more than 50% ethanol by mass. It is somewhat more soluble in water than the corresponding potassium salt.

Preparation
Sodium trisoxalatoferrate crystals

Sodium ferrioxalate can be obtained by mixing solutions of sodium oxalate and ferric oxalate, and waiting a few hours for the brown colour of the ferric oxalate to be replaced with the green colour of the complex anion.

3 Na
2C
2O
4 + Fe
2(C
2O
4)
3 → 2 Na
3[Fe(C
2O
4)
3]

The equilibrium is attained only slowly at room temperature. The product can then be crystallized by evaporating the solution at just below boiling until small crystals appear, then allowing it to cool. The product may also be precipitated by adding methanol or ethanol to the solution.

Some decomposition of the ferric oxalate may occur during the process, resulting in the canary-yellow insoluble iron(II) oxalate. Small amounts of hydrogen peroxide H
2O
2 may be added to keep the iron in the 3+ oxidation state.

See also

A number of other iron oxalates are known

References
  1. Weast, Robert C., ed. (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. B-149. ISBN 0-8493-0462-8.
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