# Iron(II) oxide FeO

> A black oxide that must be kept from hot air


## Objectives

- Describe two ways to prepare FeO, with their conditions.
- Describe the properties of FeO.
- Write its reactions with hot air and with dilute acids.

## 1. Iron oxides




## 2. Keep the air out?

Predict: when we heat the compound to get FeO, should air be present?

- No, air must be kept out. ✓
- Yes, air is needed to form any oxide.
- It makes no difference.

Air must be kept out: FeO is easily oxidized in hot air to $\ce{Fe2O3}$. That is why the book heats iron (II) oxalate in absence of air; the oxygen in FeO comes from the compound itself.

[ar-EG] لازم نمنع الهوا: الـ FeO بيحصله oxidation بسهولة في الهوا السخن ويبقى $\ce{Fe2O3}$. وعشان كده الكتاب بيسخّن الـ iron (II) oxalate في غياب الهوا؛ والـ oxygen اللي في الـ FeO جاي من الـ compound نفسه.
## 3. Preparation 1: heating iron(II) oxalate

Iron (II) oxalate $\ce{FeC2O4}$, an iron (II) salt. The book draws it as two COO groups joined to Fe. This is a thermal decomposition. Heating in absence of air keeps the FeO from being oxidized. Heating iron (II) oxalate in air gives FeO.


## 4. Preparation 2: reducing higher oxides

FeO is also made by reduction of higher oxides by hydrogen or carbon monoxide. Higher oxides have more oxygen per iron atom: $\ce{Fe2O3}$ and $\ce{Fe3O4}$. Why 2FeO? $\ce{Fe2O3}$ holds 2 Fe atoms, so 2 FeO form. 2 FeO hold 2 O atoms; $\ce{Fe2O3}$ had 3. The extra O joins $\ce{H2}$ as $\ce{H2O}$. Hydrogen removes oxygen: it is the reducing agent.


## 5. Your turn: from Fe₃O₄

Reduce magnetic iron oxide, $\ce{Fe3O4}$, with hydrogen at 400–700 °C. Balance the equation.


## 6. Properties: black, and easily oxidized

It is black powder, insoluble in water. It is easily oxidized in hot air: This is why its preparation needs absence of air. FeO is red.


## 7. With dilute acids: an iron(II) salt

It reacts with mineral acids forming iron (II) salts and water. FeO is a basic oxide: acid + basic oxide → salt + water. No gas forms. FeO + dilute acid gives an iron (III) salt.


## 8. Your turn

A student heats iron (II) oxalate in an open dish, in air. A red powder is left, not a black one. Why?

- Hot air reduced the FeO.
- Iron (II) oxalate does not decompose on heating.
- FeO is red, so the experiment worked.
- The FeO formed was oxidized by hot air to $\ce{Fe2O3}$. ✓

Heating in air oxidized the FeO as it formed: $\ce{4FeO + O2 -> 2Fe2O3}$. FeO is a black powder and $\ce{Fe2O3}$ is red, which is why the book heats iron (II) oxalate in absence of air.

[ar-EG] التسخين في الهوا عمل oxidation للـ FeO وهو بيتكوّن: $\ce{4FeO + O2 -> 2Fe2O3}$. الـ FeO مسحوق أسود والـ $\ce{Fe2O3}$ أحمر، وعشان كده الكتاب بيسخّن الـ iron (II) oxalate في غياب الهوا.
## 9. Summary

Prepare FeO by heating iron (II) oxalate in absence of air. Or reduce $\ce{Fe2O3}$ or $\ce{Fe3O4}$ with hydrogen or CO at 400–700 °C. FeO is a black powder, insoluble in water, easily oxidized in hot air. FeO + dilute acid → iron (II) salt + water. Give reason: iron (II) oxalate is heated in absence of air to prepare FeO. Key words: FeO is easily oxidized in hot air. Can you explain why FeO gives an iron (II) salt, not an iron (III) salt, with a dilute acid? Nothing is oxidized: iron is +2 in FeO and stays +2 in the salt. FeO is a basic oxide, so acid + FeO → iron (II) salt + water, e.g. $\ce{FeSO4}$ with dilute $\ce{H2SO4}$.



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