# Iron with hot concentrated sulphuric acid

> Two salts and sulphur dioxide


## Objectives

- Write the balanced equation of iron with hot concentrated sulphuric acid.
- Contrast its products with those of dilute sulphuric acid.

## 1. Properties of iron




## 2. Same acid, but hot and concentrated

Predict: which gas forms now?

- Sulphur dioxide, $\ce{SO2}$ ✓
- Hydrogen, as with the dilute acid
- No gas
- Oxygen

Hot and concentrated, $\ce{H2SO4}$ acts as an oxidizing agent: its sulphur is reduced from +6 to +4, so the gas formed is sulphur dioxide, $\ce{SO2}$, not hydrogen. No oxygen gas is released.

[ar-EG] وهو مركّز وسخن، الـ $\ce{H2SO4}$ بيشتغل oxidizing agent: الـ sulphur بتاعه بيتختزل من +6 لـ +4، فالغاز اللي بيتكوّن هو sulphur dioxide، $\ce{SO2}$، مش hydrogen. ومفيش oxygen gas بيطلع.
## 3. The book's equation

Iron reacts with hot concentrated sulphuric acid producing iron (II) sulphate, iron (III) sulphate, sulphur dioxide and water. Hot concentrated $\ce{H2SO4}$ gives $\ce{H2}$ gas with iron, like the dilute acid.


## 4. Two salts, not one

$\ce{FeSO4}$ iron (II) sulphate: iron +2 $\ce{Fe2(SO4)3}$ iron (III) sulphate: iron +3 3 Fe atoms react. One ends in $\ce{FeSO4}$, two end in $\ce{Fe2(SO4)3}$. Iron with hot concentrated $\ce{H2SO4}$ forms only iron (III) sulphate.


## 5. Worked: check the balance

A long equation is easy to misremember. Count each atom on both sides. 3Fe + 8H₂SO₄ → FeSO₄ + Fe₂(SO₄)₃ + 4SO₂ + 8H₂O Tip: the 8 appears twice, for the acid and for the water.


## 6. Rebuild it

Fill in the coefficients of the book's equation.


## 7. Dilute or hot concentrated?

Copper does not react with dilute $\ce{H2SO4}$, but it reacts with hot concentrated $\ce{H2SO4}$. Which gas forms?

- $\ce{O2}$
- $\ce{SO2}$ ✓
- $\ce{H2}$

Copper is below hydrogen, so it does not react with dilute $\ce{H2SO4}$. The hot concentrated acid acts as an oxidizing agent: it oxidizes copper and its sulphur is reduced to $\ce{SO2}$.

[ar-EG] الـ copper تحت الـ hydrogen، فمش بيتفاعل مع الـ dilute $\ce{H2SO4}$. إنما الـ acid المركّز السخن بيشتغل oxidizing agent: بيأكسد الـ copper والـ sulphur بتاعه بيتختزل لـ $\ce{SO2}$.
## 8. Summary

Iron with sulphuric acid: products (book p.21) Iron + hot concentrated $\ce{H2SO4}$ → $\ce{FeSO4}$ + $\ce{Fe2(SO4)3}$ + $\ce{SO2}$ + water. No hydrogen: the acid's sulphur is reduced, +6 → +4 in $\ce{SO2}$. Iron + dilute $\ce{H2SO4}$ → $\ce{FeSO4}$ + $\ce{H2}$: an iron (II) salt, not an iron (III) salt. Write the equation with coefficients 3, 8 → 1, 1, 4, 8 and the conditions (conc., Δ). Can you explain why the hot concentrated acid gives no hydrogen gas?



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