Sodium ferrate

Sodium ferrate is a compound with a formula of Na₂FeO₄. It is a very elusive sodium salt of ferric acid. Ferric acid is extremely unstable and does not exist under normal conditions in any way, shape, form or concentration. Its salts also tend to be unstable, sodium ferrate in particular.

Properties

Physical

Those chosen few who have seen sodium ferrate as a dry solid, describe it similarly to potassium ferrate: a dark crystalline solid that dissolves in water to form red-purple solutions. Sodium ferrate is extremely soluble, and this is the reason why it is so hard to isolate it as a pure solid: it cannot be displaced from the solution by excess NaOH. Other methods of crystallization, such as boiling the solution down, are too harsh for the unstable ferrate ion, and tend to decompose it completely.

Chemical

Sodium ferrate is a very strong oxidizer, stronger and more reactive than potassium ferrate. Generally, however, their properties are similar.

Availability

This is an exceptionally rare chemical, it is usually not stocked by any major suppliers, including Sigma-Aldrich.

Preparation

It is relatively easy to prepare an aqueous solution of sodium ferrate: the same two methods that are used for synthesizing potassium ferrate, namely the electrolytic method and the hypochlorite method, will work here. However, the resulting red-purple solution is more or less a dead end: there's no way to turn it into the pure solid in an amateur setting.

Another, non-aqueous way to prepare this compound involves a precursor chemical, sodium ferrate (IV), or sodium hypoferrate Na₄FeO₄. This crystalline solid is stable when anhydrous, but extremely unstable towards disproportionation in solution. It disproportionates into sodium ferrate, sodium hydroxide and iron (III) hydroxide instantly on contact with water.

Sodium hypoferrate is synthesized in crucibles with the following reaction:

8Na₂O + 2Fe₂O₃ + O₂ —> 4Na₄FeO₄

This requires blowing hot oxygen or air through the crucible. If you cannot do that, you can use sodium peroxide for that:

8Na₂O₂ + 2Fe₂O₃ —> 4Na₄FeO₄ + 3O₂

Handling

Safety

Sodium ferrate is non-toxic. The products of its decomposition aren't toxic either. However, dry sodium ferrate should not come in contact with flammable organic compounds.

Storage

Sodium ferrate should be stored in a dark place, without access to air (it reacts with carbon dioxide in the air). Ideally, it should be kept under vacuum or inert gas.

Disposal

Sodium ferrate solutions can just be poured into the ground or drain. Contact with any organics causes the ferrate to be quickly reduced and decomposed.