Britannica Sources used in this answer

Why do iron oxides react with strong acids but not dissolve in water?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Iron oxides are ionic compounds consisting of metal cations and oxide anions. Their chemical behavior is defined by their basic nature, which dictates how they interact with other substances.1

Iron oxides do not dissolve in water because they are stable ionic solids. However, they react with strong acids in neutralization reactions. In these processes, the oxide ions react with the hydrogen ions from the acid to form water, while the metal cations combine with the acid's anions to produce iron salts. For example, hematite reacts with hydrochloric acid according to the following equation:21

$F e_{2} O_{3} + 6 H C l \to 2 F e C l_{3} + 3 H_{2} O$

This reactivity is a characteristic property of basic transition metal oxides with oxidation numbers of +1, +2, or +3. Unlike amphoteric oxides, which can dissolve in both acidic and basic solutions, iron oxides are generally classified as basic and do not exhibit solubility in water.12