Fe2O3•nH2O + 2NaOH 2Na4[Fe(H2O)(OH)7] + (n-5)H2O
Iron(III) oxide polyhydrate react with sodium hydroxide to produce heptahydroxoaquaferrate(III) sodium and water. Iron(III) oxide polyhydrate in the form of colloidal solution. Sodium hydroxide - solid. This reaction takes place at a temperature near 70°C.