# Iron(III) oxide Fe₂O₃

> The red oxide: two ways to make it


## Objectives

- Describe two ways to prepare $\ce{Fe2O3}$, with their equations and conditions.
- State where $\ce{Fe2O3}$ occurs and its use.
- Write the reaction of $\ce{Fe2O3}$ with hot concentrated acids.

## 1. Iron oxides




## 2. What is left after heating?

Predict: what is the red solid?

- FeS
- $\ce{Fe2O3}$ ✓
- Iron metal
- FeO

The red solid is $\ce{Fe2O3}$: $\ce{2FeSO4 -> Fe2O3 + SO2 + SO3}$. Iron (II) is oxidized to iron (III), and the sulphur leaves in the two gases.

[ar-EG] المادة الصلبة الحمرا هي $\ce{Fe2O3}$: $\ce{2FeSO4 -> Fe2O3 + SO2 + SO3}$. الـ iron (II) بيتأكسد (oxidized) ويبقى iron (III)، والـ sulphur بيطلع مع الغازين.
## 3. Preparation 1: from an iron(III) salt

On adding an alkali to an aqueous solution of iron (III) salts, the (reddish brown) iron (III) hydroxide precipitates. Partners swap: a double displacement. $\ce{Fe(OH)3}$ does not dissolve, so it precipitates. The whole route; the second arrow comes next.


## 4. Heat the hydroxide

Heating iron (III) hydroxide above 200 °C converts it to iron (III) oxide. Balance the equation.


## 5. Preparation 2: heating iron(II) sulphate

Two gases leave: sulphur dioxide and sulphur trioxide. Heating $\ce{FeSO4}$ gives FeO, or only $\ce{SO2}$. Why two gases? 2 S on the left: one leaves in SO₂, one in SO₃. Iron is oxidized: +2 → +3. To pay for that, one S is reduced: +6 → +4 in SO₂. The other S stays +6 in SO₃.


## 6. In nature and in paints

This oxide is present in nature in the form of hematite. It is insoluble in water. It is used in red pigments in paints. Hematite is the red iron ore you met in the extraction unit.


## 7. With hot concentrated acids

It reacts with hot conc. mineral acids to form iron (III) salts and water. Iron stays +3, so the salt is an iron (III) salt. No gas forms. $\ce{Fe2O3}$ reacts with cold dilute acids, like FeO.


## 8. Your turn

An alkali is added to iron (III) nitrate solution, $\ce{Fe(NO3)3}$. What forms first?

- Nothing: only $\ce{FeCl3}$ gives this precipitate
- Hydrogen gas
- $\ce{Fe2O3}$ directly
- A reddish brown precipitate of $\ce{Fe(OH)3}$ ✓

A reddish brown precipitate of $\ce{Fe(OH)3}$ forms first: an alkali gives this precipitate with an aqueous solution of iron (III) salts, and iron (III) nitrate is one of them. The oxide forms only after the hydroxide is heated above 200 °C.

[ar-EG] اللي بيتكوّن الأول هو precipitate لونه reddish brown من الـ $\ce{Fe(OH)3}$: الـ alkali بيدّي الـ precipitate ده مع محلول الـ iron (III) salts، والـ iron (III) nitrate واحد منهم. والـ oxide مش بيتكوّن غير بعد ما الـ hydroxide يتسخّن فوق 200 °C.
## 9. Summary

Alkali + iron (III) salt → reddish brown $\ce{Fe(OH)3}$; above 200 °C → $\ce{Fe2O3}$ + water. Heating $\ce{FeSO4}$ → $\ce{Fe2O3}$ + $\ce{SO2}$ + $\ce{SO3}$. Found as hematite; insoluble in water; used in red pigments in paints. Hot conc. acid + $\ce{Fe2O3}$ → iron (III) salt + water. MCQ (Q1.6): heating iron (II) sulphate produces iron (III) oxide, sulphur dioxide and sulphur trioxide. Can you explain why heating $\ce{FeSO4}$ gives two different sulphur gases? Iron is oxidized from +2 to +3. To pay for that, one S is reduced from +6 to +4 and leaves in $\ce{SO2}$; the other S stays +6 and leaves in $\ce{SO3}$.



Chapter: Transition Elements (https://yaani.ai/ar/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/ar/lesson/chem-s3-en.lesson-fe.oxide-fe2o3