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2.7.9Inorganic Chemistry

Practical: Prepare Lead(II) Sulfate — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 5 parts Lesson 23 of 23 Unit quiz

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Part 1 of 5Why Precipitation?

2.7.9 Practical: Prepare Lead(II) Sulfate

Lead(II) sulfate cannot be made by the acid and metal method because it is insoluble.

Insoluble product
  • Lead(II) sulfate does not dissolve in water, so it appears as a white solid when the two solutions are mixed.
Soluble reactants
  • Both reactants must be solublelead(II) nitrate and potassium sulfate both dissolve.
Equation
  • The balanced equation is Pb(NO₃)₂(aq) + K₂SO₄(aq) → PbSO₄(s) + 2KNO₃(aq).
Ionic equation
  • Pb²⁺(aq) + SO₄²⁻(aq) → PbSO₄(s) shows what actually happens.

Part 2 of 5Method

The steps are filter, wash and dry.

1
Measure 25 cm³ of 0.5 mol/dm³ lead(II) nitrate solution into a small beaker.
2
Add 25 cm³ of 0.5 mol/dm³ potassium sulfate solution and stir with a glass rod; a white precipitate forms.
3
Filter the mixture, collecting the white solid in the filter paper.
4
Wash the solid with distilled water to remove traces of the other solutions.
5
Dry the precipitate in a warm oven or between filter papers.

Part 3 of 5Safety and Handling

Safety and Handling
Toxicity
  • Lead compounds are toxic, so avoid skin contact and do not breathe dust.
Protection
  • Wear eye protection and gloves and wash hands after the practical.
Waste
  • Lead waste must be collected for proper disposal and not poured down the sink.
Spectator ions
  • Potassium and nitrate ions stay dissolved in the filtrate and take no part in forming the solid.

Part 4 of 5Understanding the Result

Understanding the Result
Mole ratio
  • 25 cm³ of each 0.5 mol/dm³ solution contains 0.0125 mol, so the ions react in a 1:1 ratio with no excess.
Maximum mass
  • Moles of PbSO₄ = 0.0125, and Mr is 303, so the theoretical mass is 3.79 g.
Filtrate
  • The solution that passes through the filter paper contains potassium nitrate, which is soluble.
Purity
  • Washing is essential because potassium nitrate solution would otherwise dry on to the product.

Part 5 of 5Exam Checklist & Tips

2.7.9 – Key Points for the Exam

  • Precipitate An insoluble solid formed by a reaction in solution.
  • Double decomposition A reaction in which two compounds exchange ions to form two new compounds.
  • Residue The solid left on the filter paper.
  • Spectator ion An ion that is present but does not take part in the reaction.

Common Mistakes

  • Describing the product as dissolving in water; lead(II) sulfate is insoluble.
  • Forgetting to wash the precipitate, so soluble potassium nitrate contaminates it.
  • Putting lead waste down the sink.
  • Including spectator ions K⁺ and NO₃⁻ in the ionic equation.

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