Iron(III) nitrate, or ferric nitrate, is the name used for a series of inorganic compounds with the formula Fe(NO3)3.(H2O)n. Most common is the nonahydrate Fe(NO3)3.(H2O)9. The hydrates are all pale colored, water-soluble paramagnetic salts.

Hydrates

Iron(III) nitrate is deliquescent, and it is commonly found as the nonahydrate Fe(NO3)3·9H2O, which forms colourless to pale violet crystals. This compound is the trinitrate salt of the aquo complex [Fe(H2O)6]3+. Other hydrates ·x, include:

Reactions

Iron(III) nitrate is a useful precursor to other iron compounds because the nitrate is easily removed or decomposed. It is for example, a standard precursor to potassium ferrate K2FeO4. When dissolved, iron(III) nitrate forms yellow solutions. When this solution is heated to near boiling, nitric acid evaporates and a solid precipitate of iron(III) oxide appears. Another method for producing iron oxides from this nitrate salt involves neutralizing its aqueous solutions.

Preparation

The compound can be prepared by treating iron metal powder with nitric acid, as summarized by the following idealized equation:

Applications

Ferric nitrate has no large scale applications. It is a catalyst for the synthesis of sodium amide from a solution of sodium in ammonia: Certain clays impregnated with ferric nitrate have been shown to be useful oxidants in organic synthesis. For example, ferric nitrate on Montmorillonite—a reagent called Clayfen—has been employed for the oxidation of alcohols to aldehydes and thiols to disulfides. Ferric nitrate solutions are used by jewelers and metalsmiths to etch silver and silver alloys.