Iron with non-metals: chlorine and sulphur

Iron(III) with chlorine, iron(II) with sulphur

1. Properties of iron

Iron with non-metals: chlorine and sulphur

2. Same metal, two partners

Heat iron in chlorine gas, or with sulphur powder. Both react. Do they give iron the same oxidation state?

Pick the right answer

Predict: what does iron form with chlorine?

A. $FeCl2 FeCl X_{2}$ , iron(II) chloride
B. $FeCl3 FeCl X_{3}$ , iron(III) chloride
C. Nothing: iron reacts only with oxygen

الشرح

Heated iron reacts with chlorine to give iron(III) chloride:

2Fe + 3Cl2 \to 2FeCl3 2 Fe + 3 Cl X_{2} 2 FeCl X_{3}

. Chlorine takes iron to the +3 oxidation state.

3. With chlorine: iron(III) chloride

gathered2Fe(s) + 3Cl2(g) →[Δ]\\ 2FeCl3(s)gathered

Iron reacts with chlorine producing iron (III) chloride.

Each Cl is −1. Three Cl give −3, so iron is +3.

4. With sulphur: iron(II) sulphide

Fe(s) + S(s) \to[Δ] FeS(s) Fe (s) + S (s) Δ FeS (s)

Iron reacts with sulphur producing iron (II) sulphide.

Chlorine

Strong oxidizing agent →

FeCl3 FeCl X_{3}

, iron +3

Sulphur

Weaker oxidizing agent → FeS, iron +2

In a sulphide, sulphur is −2. So iron is +2 in FeS.

5. Worked: balancing iron + chlorine

Formulas first: Fe + $Cl2 Cl X_{2}$ → $FeCl3 FeCl X_{3}$ . Chlorine gas comes as $Cl2 Cl X_{2}$ molecules.
Cl: 2 on the left, 3 on the right. The lowest common multiple is 6.
6 Cl = 3 $Cl2 Cl X_{2}$ on the left and 2 $FeCl3 FeCl X_{3}$ on the right.
Now there are 2 Fe on the right, so write 2Fe on the left.

2Fe + 3Cl2 \to[Δ] 2FeCl3 2 Fe + 3 Cl X_{2} Δ 2 FeCl X_{3}

Check: 2 Fe and 6 Cl on each side.

6. Your turn: a new metal

Balance the equation

Aluminum also reacts with chlorine on heating, giving

AlCl3 AlCl X_{3}

. Balance the equation.

Al + Cl2 \to[Δ] AlCl3 □ Al + □ Cl X_{2} Δ □ AlCl X_{3}

Balanced equation

2Al + 3Cl2 \to[Δ] 2AlCl3 2 Al + 3 Cl X_{2} Δ 2 AlCl X_{3}

الشرح

Same pattern: 6 Cl atoms = 3

Cl2 Cl X_{2}

= 2

AlCl3 AlCl X_{3}

, so 2 Al.

Need a hint?

Which atom appears as a pair on the left and as a three on the right?
What is the lowest common multiple of 2 and 3?
How many $AlCl3 AlCl X_{3}$ hold that many Cl atoms? Then fix Al.

7. Iron(II) or iron(III)?

Sort into groups

Find the oxidation state of iron in each compound.

$Fe2O3 Fe X_{2} O X_{3}$ $FeSO4 FeSO X_{4}$ $FeCO3 FeCO X_{3}$ $Fe2(SO4)3 Fe X_{2} (SO X_{4}) X_{3}$

Pick the right answer

A student writes

Fe + S \to FeSO4 Fe + S FeSO X_{4}

. What is wrong?

A. There is no oxygen on the left, so a sulphate cannot form.
B. Nothing: heating iron with sulphur gives a sulphate.
C. The product should be $Fe2S3 Fe X_{2} S X_{3}$ , iron(III) sulphide.
D. Iron does not react with sulphur.

الشرح

The left side holds Fe and S with no oxygen, so a sulphate cannot form. Heated iron and sulphur give iron(II) sulphide:

Fe + S \to FeS Fe + S FeS

8. Summary

Iron + chlorine → iron (III) chloride: $2Fe + 3Cl2 \to 2FeCl3 2 Fe + 3 Cl X_{2} 2 FeCl X_{3}$ . Iron is +3.
Iron + sulphur → iron (II) sulphide: $Fe + S \to FeS Fe + S FeS$ . Iron is +2.
Sulphur is a weaker oxidizing agent than chlorine, so iron stops at +2.
No oxygen reacts, so no sulphate forms.

Can you explain why iron is +3 in

FeCl3 FeCl X_{3}

but +2 in FeS?

Reveal

Each Cl is −1, so three Cl give −3 and iron is +3 in

FeCl3 FeCl X_{3}

. In a sulphide, sulphur is −2, so iron is +2 in FeS. Chlorine is a strong oxidizing agent; sulphur is a weaker one.

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