A student wants to prepare a pure, dry sample of lead(II) sulfate. Lead(II) sulfate is an insoluble salt. Describe how the student could prepare this salt by mixing two solutions together, and explain how the product is separated and dried.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Lead(II) sulfate is an insoluble white solid that does not dissolve in water. It can be made by a precipitation reaction.
Model answer (4 marks)
1. Dissolve a soluble lead(II) salt (e.g. lead(II) nitrate) in water.
2. Dissolve a soluble sulfate (e.g. sodium sulfate or dilute sulphuric acid) in a separate beaker.
3. Slowly pour the sulfate solution into the lead(II) solution while stirring.
4. Lead(II) sulfate precipitates as a white solid.
5. Filter the mixture to collect the precipitate.
6. Wash the solid with distilled water to remove soluble impurities.
7. Dry the residue by heating in an oven or leaving it in a warm place or in a desiccator until constant mass is achieved.
2. Dissolve a soluble sulfate (e.g. sodium sulfate or dilute sulphuric acid) in a separate beaker.
3. Slowly pour the sulfate solution into the lead(II) solution while stirring.
4. Lead(II) sulfate precipitates as a white solid.
5. Filter the mixture to collect the precipitate.
6. Wash the solid with distilled water to remove soluble impurities.
7. Dry the residue by heating in an oven or leaving it in a warm place or in a desiccator until constant mass is achieved.
Examiner tips
- Use the word ‘precipitate’ to show understanding of the reaction.
- Show the sequence: dissolve, mix, filter, wash, dry – each step earns a point.
- Mention a clean filter paper and a drying method that gives a dry solid.
Common mistakes
- Failing to specify that the lead salt is soluble (e.g. using lead(II) sulfate itself).
- Omitting the washing step, leaving soluble impurities in the product.
- Not stating that the solid must be dried to a constant mass.
Mark scheme (4 marks)
- Mix solutions of a soluble lead(II) salt (e.g. lead(II) nitrate) and a soluble sulfate (e.g. sodium sulfate / dilute sulfuric acid) together
- Filter the mixture to collect the precipitate
- Wash the residue with distilled water to remove soluble impurities
- Dry the solid by heating in an oven or leaving in a warm place / desiccator
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
More Preparation of salts questions
- Describe how a pure, dry sample of sodium chloride could be prepared by reacting…
- Describe how a pure, dry sample of ammonium sulfate could be prepared in the lab…
- Zinc chloride can be prepared by reacting zinc carbonate with dilute hydrochlori…
- Describe how a pure, dry sample of copper(II) sulfate crystals could be prepared…