Iron and Its Oxides – Making FeO, Fe₃O₄ and Fe₂O₃, Testing Fe²⁺ and Fe³⁺

What it shows

Iron forms three common oxides. Heating iron(II) oxalate without air leaves black FeO; steam over hot iron gives black Fe₃O₄ and hydrogen; heating iron(II) sulfate crystals gives red-brown Fe₂O₃ with SO₂ and SO₃. Weighing the solid before and after gives the oxygen-to-iron ratio of each product. Dilute acids dissolve the oxides without changing the oxidation state, so FeO gives Fe²⁺, Fe₂O₃ gives Fe³⁺ and Fe₃O₄ gives both. NaOH, KSCN and K₃[Fe(CN)₆] tell the ions apart. Fe²⁺ is [Ar]3d⁶ and Fe³⁺ is [Ar]3d⁵, so Fe²⁺ loses one paired electron to reach a half-filled subshell. Times in air are shortened, and the masses are those of complete reactions.

How to use

On Make the oxides, choose FeO, Fe₃O₄ or Fe₂O₃, set the Starting mass and press Heat; each result goes in the table. Clear Air kept out to see what air does to FeO. On Acid and ion tests, choose an oxide, press Dissolve, then press NaOH, KSCN and K₃[Fe(CN)₆]. Use Leave 10 min in air and test again. Choose Unknown to identify a solution. On Electron boxes, choose Fe, Fe²⁺ or Fe³⁺.

Parameters you can change

• Screen Make the oxides, Acid and ion tests, Electron boxes
• Oxide to make FeO, Fe₃O₄, Fe₂O₃
• Starting mass 1–5 g
• Air kept out
• Oxide dissolved FeO, Fe₃O₄, Fe₂O₃, Unknown solution
• Dilute acid H₂SO₄, HCl
• Atom or ion Fe, Fe²⁺, Fe³⁺

Questions to explore

1. Which oxide gives both a blood-red colour with KSCN and a dark blue precipitate with K₃[Fe(CN)₆] after dissolving in acid?
2. What solid is left if iron(II) oxalate is heated with air, and what oxygen-to-iron ratio do your masses give?
3. Why does a fresh Fe²⁺ solution begin to turn red with KSCN after standing in air?