Chemistry · Salts · Acid + base/carbonate

Preparing a soluble salt

When the metal is less reactive than zinc, its oxide or carbonate is added in excess to a warm acid. The acid is fully neutralised; the remaining solid is filtered off; the salt solution is then evaporated and crystallised.

1

Add the solid to warm acid in a beaker, stir

2

Keep adding until no more dissolves (excess)

3

Filter to remove unreacted solid

4

Heat filtrate to evaporate half the water

5

Allow to cool and crystallise

6

Filter and dry the crystals

Copper(II) sulfate: recipe

acid: H₂SO₄(aq)
base/carbonate: CuO (copper(II) oxide — black)
CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)

Exam-style questions

1. Why is EXCESS solid added to the acid?

2. When making CuCl₂ from CuCO₃ + HCl, you observe fizzing. What is the gas?

3. Why is the filtrate EVAPORATED only PART of the way (not boiled to dryness)?

4. The 'acid + carbonate / oxide' route is suitable for the salts of which kinds of metal?