Chemistry • Year 11 • Module 3 • Lesson 3
Precipitation & Solubility Rules
Lock in the NAGSAG solubility rules, the vocabulary of ionic equations, and the skill of predicting precipitate formation from first principles.
1. Term–definition match
Match each term to its correct definition. Write the matching term in the right-hand column. Terms to use: precipitation reaction, solubility rules (NAGSAG), net ionic equation, spectator ions, precipitate, double displacement, Ksp (solubility product), full ionic equation. 8 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | An insoluble solid that forms when two aqueous solutions are mixed and the ion product exceeds the compound's maximum solubility. | |
| 1.2 | A reaction in which two ionic compounds in aqueous solution exchange anion partners, producing a product that is insoluble, a gas, or a weak electrolyte. | |
| 1.3 | Ions present in solution that appear unchanged on both sides of the full ionic equation and play no role in the reaction. | |
| 1.4 | A mnemonic framework (Nitrates, Ammonium, Group 1, Sulfates, Acetates, Group 17) used to predict whether an ionic compound will dissolve or precipitate. | |
| 1.5 | An ionic equation from which all spectator ions have been removed, showing only the particles that actually react. | |
| 1.6 | The equilibrium constant describing the maximum product of ion concentrations for a sparingly soluble ionic compound in a saturated solution. | |
| 1.7 | An equation in which every soluble ionic compound is written as separate aqueous ions, while precipitates, liquids, and gases remain intact. | |
| 1.8 | A reaction in which two aqueous ionic solutions mix and an insoluble solid forms: A(aq) + B(aq) → solid + remaining solution. |
2. Complete the NAGSAG solubility table
Fill in the missing cells. Each blank requires either "All soluble", "Mostly soluble", "Mostly insoluble", or the correct exception ions. 8 marks (1 each)
| Ion / group | General solubility | Exceptions (insoluble WITH these cations) |
|---|---|---|
| NO3− (nitrate) | None | |
| NH4+ (ammonium) | All soluble | |
| Group 1 metal ions (Li+, Na+, K+, …) | None | |
| SO42− (sulfate) | Mostly soluble | |
| CH3COO− (acetate) | None | |
| Cl−, Br−, I− (halides) | Mostly soluble | |
| CO32− (carbonate) | Soluble WITH Group 1 and NH4+ | |
| OH− (hydroxide) | Mostly insoluble |
3. True or false — with correction
Circle T or F. If false, write the corrected version on the line. 10 marks (1 T/F + 1 correction each)
3.1 All ionic compounds dissolve in water because water is a polar molecule. T / F
3.2 Lead(II) iodide (PbI2) is soluble because iodide is a Group 17 halide. T / F
3.3 In a full ionic equation, the precipitate is written as separate aqueous ions. T / F
3.4 Spectator ions are omitted from the net ionic equation because they do not participate in the reaction. T / F
3.5 Calcium sulfate (CaSO4) is soluble because calcium is often soluble with other anions. T / F
4. Common precipitate colours
Complete the table by filling in the precipitate colour and the relevant insolubility rule that explains why it forms. 6 marks (1 each)
| Precipitate | Colour | Rule that makes it insoluble |
|---|---|---|
| AgCl(s) | Ag+ is an exception for halides | |
| BaSO4(s) | White | |
| PbSO4(s) | Pb2+ is an exception for sulfates | |
| Fe(OH)3(s) | Fe3+ is not Group 1 — hydroxide rule applies | |
| CaCO3(s) | White | |
| HgS(s) | Sulfide with non-Group 1, non-NH4+ cation |
5. Fill the blanks — ionic equations
Complete the paragraph using words from the word bank. Each word is used once. 8 marks (1 each)
Word bank: net ionic, spectator, insoluble, precipitate, full ionic, aqueous, solid, solubility rules
When two ionic solutions are mixed, chemists use ______________ to predict whether a reaction will occur. If at least one of the possible product combinations forms an ______________ compound, a ______________ will appear as a ______________ in the solution. To represent this reaction, we can write three types of equations. The molecular equation uses complete formulas. The ______________ equation splits all ______________ (aq) ionic compounds into their separate ions, keeping the precipitate intact as a formula unit. Finally, the ______________ equation is obtained by removing the ______________ ions, leaving only the particles that actually react.
6. Build a concept map
Draw labelled arrows between the five terms below to show how they connect. Each arrow must carry a linking phrase (e.g. "is predicted using", "produces", "removes"). Aim for at least 5 labelled arrows. 5 marks
Supplied terms: solubility rules · double displacement reaction · precipitate · net ionic equation · spectator ions
Q1 — Term–definition matches
1.1 precipitate • 1.2 double displacement • 1.3 spectator ions • 1.4 solubility rules (NAGSAG) • 1.5 net ionic equation • 1.6 Ksp (solubility product) • 1.7 full ionic equation • 1.8 precipitation reaction.
Q2 — NAGSAG table
Nitrate row: All soluble. Ammonium exceptions: None. Group 1 solubility: All soluble. Sulfate exceptions: Ba2+, Pb2+, Ca2+. Acetate solubility: All soluble. Halide exceptions: Ag+, Pb2+. Carbonate solubility: Mostly insoluble. Hydroxide exceptions: Soluble with Group 1 and Ba2+.
Q3 — True / false
3.1 False. Solubility depends on the balance between lattice energy and hydration energy — many ionic compounds are insoluble despite water's polarity (e.g. AgCl, BaSO4).
3.2 False. Pb2+ is an exception to the halide rule — PbI2 is insoluble (forms a bright yellow precipitate).
3.3 False. In a full ionic equation the precipitate is kept intact as a solid formula unit (e.g. PbI2(s)), not split into ions.
3.4 True.
3.5 False. CaSO4 is insoluble — Ca2+ is one of the three exceptions to the sulfate rule (along with Ba2+ and Pb2+).
Q4 — Precipitate colours
AgCl — white. BaSO4 — rule: Ba2+ is a sulfate exception. PbSO4 — white. Fe(OH)3 — rust brown. CaCO3 — rule: Ca2+ is not Group 1 or ammonium, so carbonate is insoluble. HgS — black.
Q5 — Cloze answers (in order)
solubility rules / insoluble / precipitate / solid / full ionic / aqueous / net ionic / spectator.
Q6 — Sample concept map
Award 1 mark per valid labelled arrow (at least 5). Sample links:
- solubility rules — predict whether → precipitate forms
- double displacement reaction — may produce → precipitate
- double displacement reaction — is represented by → net ionic equation
- net ionic equation — is obtained by removing → spectator ions
- spectator ions — do not appear in → net ionic equation
- precipitate — is not split in → net ionic equation