Topic 5 of 7
Use solubility rules to choose starting materials
An insoluble product can be separated as a precipitate.
O-Level 6092 (2026) / SEC G3 K324 (2027)
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Use solubility rules to choose starting materials
An insoluble product can be separated as a precipitate.
| Family | Rule and important exceptions |
|---|---|
| Group 1 and ammonium salts | Soluble |
| Nitrates | Soluble |
| Chlorides | Generally soluble; silver chloride and lead(II) chloride are exceptions |
| Sulfates | Generally soluble; barium sulfate and lead(II) sulfate are insoluble; calcium sulfate is sparingly soluble |
| Carbonates | Generally insoluble except Group 1 and ammonium carbonates |
| Hydroxides | Generally insoluble except Group 1 hydroxides; calcium hydroxide is slightly soluble |
Precipitation occurs when dissolved ions meet and form an insoluble solid. Mixing Ba(NO3)2(aq) and Na2SO4(aq) gives BaSO4(s). The ionic equation is Ba2+(aq) + SO42-(aq) -> BaSO4(s). Choose soluble starting salts so both required ions are available to mix.
Check your understandingWhy mix barium nitrate solution with sodium sulfate solution rather than simply mixing the dry solids?Think it through, then reveal the answer
Dissolved Ba2+ and SO4 2- ions can move and meet to form insoluble barium sulfate. Dry ionic solids do not provide freely mixing ions; using solutions makes precipitation effective.