3.1.3 - Laboratory Activity: Change of iron (III) ions to iron (II) ions

Laboratory Activity 3.1.3: Change of iron (III) ions to iron (II) ions

Aim: To understand the change of iron (III) ions, Fe³⁺ to iron (II) ions, Fe²⁺ in the redox reaction.

Material: » Iron (III) sulphate solution » Zinc powder » Magnesium powder » Sodium hydroxide solution

Apparatus: » Test tube » Test tube holders » Dropper » Filter paper » Filter funnel » Bunsen burner

Procedure:

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(A) With chlorine 1. 2cm3 of iron (III) sulphate is poured into a test tube. 2. Half a spatula of zinc powder is added into the solution and the mixture is heated. 3. Filter the mixture and add sodium hydroxide solution slowly. Observed the changes occur. 4. The experiment is repeated with magnesium powder to replace the zinc powder

Observation:

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Reagents Observation Zinc + iron (III) sulphate + heat Zinc dissolved and the colour of the solution changed to light green. Zinc + iron (III) sulphate + sodium hydroxide solution A greenish precipitate was formed. Magnesium + iron (III) sulphate + heat Magnesium dissolved and the colour of the solution changed from brown to light green. Zinc + iron (III) sulphate + sodium hydroxide solution A greenish precipitate was formed.

Analysis:

	►	Iron (III) with zinc ○ Half ionic equation: ■ Zn(s) → Zn2+(aq) + 2e− (oxidation → reducing agent: zinc) ■ Fe3+(aq) + e− → Fe2+(aq) (reduction → oxidising agent: iron (III) ions, Fe3+) ○ Overall equation: ■ Zn(s) + 2Fe3+(aq) → Fe2+(aq) + Zn2+(aq) ○ Zinc powder dissolves in the solution and the brown solution turn to green. ○ A green precipitate is produced when the sodium hydroxide solution is added. This confirm the presence of iron(II). ■ Fe2+(aq) + 2OH−(aq) → Fe(OH)2(aq) (greenish percipitate)
	►	Iron (III) with magnesium ○ Half ionic equation: ■ Mg(s) → Mg2+(aq) + 2e− (oxidation → reducing agent: magnesium) ■ 2Fe3+(aq) + 2e− → 2Fe2+(aq) (reduction → oxidising agent: iron (III) ions, Fe3+) ○ Overall equation: ■ Mg(s) + 2Fe3+(aq) → 2Fe2+(aq) + Mg2+(aq) ○ Magnesium dissolves in the solution and the brown solution turn to green. ○ A green precipitate is produced when the sodium hydroxide solution is added. This confirm the presence of iron(II). ■ Fe2+(aq) + 2OH−(aq) → Fe(OH)2(aq) (greenish percipitate)

Conclusion:

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Magnesium and zinc reduced Fe3+ to Fe2+

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