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

Laboratory Activity 3.1.2: Change of iron (II) ions to iron (III) ions

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

Material: » Iron (II) sulphate solution » Sodium hydroxide solution » Bromine water

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

Procedure:

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1. 2cm3 of iron (II) sulphate is poured into a test tube. 2. Sodium hydroxide solution is added to the solution. Change in the solution that took place is recorded. 3. Repeat step 1. A few drops of bromine water is added drop by drop using dropper into the test tube until no further change is observed. 4. Each test tube are heated slowly 5. Sodium hydroxide solution is then added until no further change is observed.

Observation:

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Reagents Observation Iron (II) sulphate + sodium hydroxide A greenish brown precipitate was observed Iron (II) + bromine water Bromine water was decolourised Iron (II) sulphate + bromine water + sodium hydroxide A reddish brown precipitate was observed

Analysis:

	►	Iron (II) sulphate + sodium hydroxide ○ Iron (II) sulphate reacted with sodium hydroxide to give a greenish precipitate. This shows that Fe2+ ions are present. ○ Fe2+(aq) + 2OH−(aq) → Fe(OH)2 (greenish percipitate)
	►	Iron (II) + bromine water ○ Half ionic equation: ■ Fe2+(aq) → Fe3+(aq) + e− (oxidation → reducing agent: iron (II) ions, Fe2+) ■ Br2(aq) + 2e− → 2Br−(aq) (reduction → oxidising agent: bromine water) ○ Overall equation: ■ 2Fe2+(aq) + Br2(aq) → Fe2+(aq) + 2Br−(aq) ○ The ion solution turned from greenish colour to brownish colour and the brown coloured bromine colour water is decolourised.
	►	Iron (II) sulphate + bromine water + sodium hydroxide ○ Iron (III) sulphate reacted with sodium hydroxide to give a brownish precipitate. This shows that Fe3+ ions are present. ■ Fe3+ + 3OH−(aq) → Fe(OH)3 (brownish percipitate)

Conclusion:

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Bromine water oxidised Fe2+ to Fe3+

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