Iron with dilute acids

1. Properties of iron

2. Chlorine vs hydrochloric acid

Iron + chlorine gives iron(III) chloride,

FeCl3 FeCl X_{3}

. Hydrochloric acid, HCl, also contains chlorine.

Pick the right answer

Predict: what does iron give with dilute hydrochloric acid?

A. $FeCl3 FeCl X_{3}$ + hydrogen
B. $FeCl2 FeCl X_{2}$ + hydrogen
C. No reaction

Explanation

Iron with dilute hydrochloric acid gives iron(II) chloride and hydrogen gas:

Fe + 2HCl \to FeCl2 + H2 Fe + 2 HCl FeCl X_{2} + H X_{2}

. The hydrogen produced reduces iron(III) to iron(II), so

FeCl3 FeCl X_{3}

does not form here.

3. Iron dissolves in dilute acids

gatheredFe(s) + H2SO4(aq) →[(dil)]\\ FeSO4(aq) + H2(g)gathered

gatheredFe(s) + 2HCl(aq) →[(dil)]\\ FeCl2(aq) + H2(g)gathered

Iron dissolves in dilute mineral acids producing iron (II) salts.

Mineral acids

Inorganic acids, such as hydrochloric acid (HCl) and sulphuric acid (

H2SO4 H X_{2} SO X_{4}

).

4. Why iron(II), not iron(III)?

The book: iron (II) salts form, not iron (III) salts, which are reduced by the produced hydrogen.

Fe + dilute acid → $H2 H X_{2}$ gas forms (iron displaces H)
$H2 H X_{2}$ gas forms → iron(III) is reduced ( $H2 H X_{2}$ : reducing agent)
iron(III) is reduced → iron(II) salt (+3 → +2)

5. Worked, then faded

Iron gives an iron(II) salt: $Fe²⁺ Fe X^{2 +}$ .
Sulphuric acid gives sulphate, $SO4²⁻ SO X_{4} X^{2 -}$ : so $FeSO4 FeSO X_{4}$ .
The other product is hydrogen gas, $H2 H X_{2}$ .
Write (dil) over the arrow, and the states.

Fill in the blanks

Now a new acid, dilute hydrobromic acid: Fe + 2HBr → _____ +

H2 H X_{2}

Explanation

An iron(II) salt again:

FeBr2 FeBr X_{2}

, with hydrogen gas.

6. Give the reason

Pick the right answer

Give reason: iron reacts with dilute acids to produce iron (II) salts, not iron (III) salts.

A. The hydrogen produced reduces iron (III) to iron (II).
B. Iron has no +3 oxidation state.
C. Iron (III) is unstable, so it never forms.
D. Dilute acids contain no chlorine or sulphate.

Explanation

The book's reason: iron dissolves in dilute mineral acids giving iron(II) salts, because the hydrogen produced reduces iron(III) to iron(II).

Sort into groups

Does iron end as iron(II) or iron(III)?

Iron + chlorine, heatedIron + dilute HClIron + sulphur, heatedIron + dilute $H2SO4 H X_{2} SO X_{4}$

7. Summary

Iron dissolves in dilute mineral acids: iron (II) salt + hydrogen.
$Fe + H2SO4 \to FeSO4 + H2 Fe + H X_{2} SO X_{4} FeSO X_{4} + H X_{2}$ and $Fe + 2HCl \to FeCl2 + H2 Fe + 2 HCl FeCl X_{2} + H X_{2}$ .
Reason: the produced hydrogen reduces iron (III) to iron (II).
Contrast: chlorine gas gives $FeCl3 FeCl X_{3}$ .

Can you explain why HCl gives

FeCl2 FeCl X_{2}

, but chlorine gives

FeCl3 FeCl X_{3}

?

Reveal

With HCl, hydrogen forms, and the produced hydrogen reduces iron (III) to iron (II): so

FeCl2 FeCl X_{2}

forms. Chlorine gas forms no hydrogen, so iron ends as

FeCl3 FeCl X_{3}

.

1. Properties of iron

2. Chlorine vs hydrochloric acid

3. Iron dissolves in dilute acids

4. Why iron(II), not iron(III)?

5. Worked, then faded

6. Give the reason

7. Summary

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