Excess Solid Method — Preparing Salts
Cambridge IGCSE Chemistry 0620 · Experimental Procedures · Sections A–C
Reaction
CuO(s) + H₂SO₄(aq) →
CuSO₄(aq) + H₂O(l)
⚠️ Safety
Sulfuric acid is corrosive. Wear goggles and gloves. Heat gently — do not boil.
Step 1–3: Add Excess CuO to Warm H₂SO₄
Step 4–5: Crystallisation from Solution
Section A: Method Steps
Describe how you would obtain a solution of copper(II) sulfate from dilute sulfuric acid and copper(II) oxide.
[4 marks]A student wants to make zinc sulfate from zinc oxide and dilute sulfuric acid. Describe the method, including all practical steps.
[4 marks]State the purpose of filtering the mixture after the reaction between excess copper(II) oxide and sulfuric acid.
[1 mark]Write a word equation and a balanced symbol equation for the reaction between copper(II) oxide and sulfuric acid.
[3 marks]Describe what you would observe during the reaction of copper(II) oxide with warm sulfuric acid.
[2 marks]Section B: Crystallisation
Describe how you would obtain dry crystals of copper(II) sulfate from copper(II) sulfate solution.
[4 marks]Why must you NOT evaporate the copper(II) sulfate solution to complete dryness?
[2 marks]How would you remove the crystals from the remaining solution after cooling?
[1 mark]After filtering, how should the crystals be dried? Give a reason for your chosen method.
[2 marks]Describe the full process from copper(II) sulfate solution to dry copper(II) sulfate crystals, in the correct order.
[4 marks]Section C: Explanations
Why is copper(II) oxide added in excess when preparing copper(II) sulfate from sulfuric acid?
[2 marks]How would you know that excess copper(II) oxide has been added to the sulfuric acid?
[1 mark]Explain why the mixture must be filtered after the excess solid method, and what would happen if filtering was omitted.
[2 marks]A student used cold sulfuric acid instead of warm acid when reacting with copper(II) oxide. Explain the problem with this approach.
[2 marks]Copper(II) oxide is a base. Explain, using the definition of a base, why it reacts with sulfuric acid, and identify the type of reaction taking place.
[3 marks]🔑 Golden Rules — Excess Solid Method
✅ Add the insoluble base in excess to warm acid
✅ Excess = solid stops dissolving / remains at bottom
✅ Filter to remove excess unreacted solid
✅ Heat to point of crystallisation — not to dryness
✅ Cool slowly, then filter and pat dry
✅ Never oven-dry — removes water of crystallisation
Equation: CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l) — memorise with state symbols
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