FeNH4(SO4)2 + 4NaOH → FeO(OH) + NH3•H2O + 2Na2SO4 + H2O
Ammonium-iron(III) sulfate react with sodium hydroxide to produce iron(III) oxide-hydroxide, ammonium hydroxide, sodium sulfate and water. Sodium hydroxide - diluted solution. The reaction takes place in a boiling solution.