2.3.1Inorganic Chemistry: Part 1
Solubility Rules — Edexcel International GCSE Science Double Award (Modular) - Chemistry Unit 1 Revision Notes & Topical Questions
5 min read 10 parts Lesson 10 of 15
Part 1 of 8The rules in words
Always soluble
- Always soluble All sodium, potassium and ammonium salts dissolve in water.
- All nitrates dissolve in water.
Chlorides
- Chlorides Most chlorides are soluble.
- The exceptions are silver chloride and lead(II) chloride.
Sulfates
- Sulfates Most sulfates are soluble.
- The exceptions are barium sulfate, calcium sulfate and lead(II) sulfate.
Carbonates and hydroxides
- Carbonates and hydroxides Most carbonates and hydroxides are insoluble.
- The exceptions are those of sodium, potassium and ammonium; calcium hydroxide is only slightly soluble.
Part 2 of 8Solubility table
| Type of compound | Soluble | Insoluble |
|---|---|---|
| Group 1 and ammonium salts | All | None |
| Nitrates | All | None |
| Chlorides | Most | Silver, lead(II) |
| Sulfates | Most | Barium, calcium, lead(II) |
| Carbonates | Sodium, potassium, ammonium | Most others |
| Hydroxides | Sodium, potassium, ammonium | Most others |
Part 3 of 8Choosing a preparation method
1
Write the balanced equation to identify the salt that will be made.
2
Look up the salt in the solubility table.
3
If the salt is soluble, make it from an acid with either an insoluble base (using excess and filtering) or an alkali (using titration).
4
If the salt is insoluble, make it by mixing two soluble salt solutions in a precipitation reaction.
5
Filter the solid, wash it with distilled water and dry it.
Part 4 of 8Predicting a precipitate
1Mix two solutions
- Mix two solutions For example silver nitrate solution and sodium chloride solution.
2Swap partners
- Swap partners The ions can pair up differently, giving silver chloride and sodium nitrate.
3Check solubility
- Check solubility Nitrates are all soluble, but silver chloride is an exception that is insoluble.
4Precipitate forms
- Precipitate forms AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq); the solid is a white precipitate.
Part 5 of 8Worked predictions
| Solutions mixed | Possible new compounds | Result |
|---|---|---|
| Sodium sulfate + barium chloride | Barium sulfate + sodium chloride | White precipitate of BaSO4 |
| Copper(II) sulfate + sodium hydroxide | Copper(II) hydroxide + sodium sulfate | Blue precipitate of Cu(OH)2 |
| Potassium nitrate + sodium chloride | Potassium chloride + sodium nitrate | No precipitate, because both products are soluble |
| Lead(II) nitrate + sodium chloride | Lead(II) chloride + sodium nitrate | White precipitate of PbCl2 |
Part 6 of 8Ionic equations for precipitation
Spectator ions
- Spectator ions Ions that stay dissolved on both sides of the equation are left out, which leaves only the ions that join to form the solid.
Silver chloride
- Silver chloride Ag+(aq) + Cl−(aq) → AgCl(s)
Barium sulfate
- Barium sulfate Ba2+(aq) + SO42−(aq) → BaSO4(s)
Part 7 of 8Making a pure dry insoluble salt
1
Choose two soluble salts that contain the ions needed, for example lead(II) nitrate and sodium chloride for lead(II) chloride.
2
Mix the two solutions in a beaker and stir until no more precipitate forms.
3
Filter the mixture so the solid stays in the filter paper.
4
Wash the solid with distilled water to remove soluble impurities, then dry it in a warm oven or between filter papers.
Part 8 of 8Applying the rules
Solubility in the lab
Tests for ions
- Tests for ions Silver nitrate solution gives a white precipitate with chloride ions,
- and barium chloride solution gives one with sulfate ions,
- so precipitation can be used as a test.
Water treatment
- Water treatment Precipitation can remove unwanted metal ions from waste water by turning them into insoluble solids that can be filtered off.
Remember the exceptions
- Remember the exceptions Learn the short list of insoluble chlorides and sulfates,
- because every other chloride and sulfate you meet at this level is soluble.
Key terms
| Term | Meaning |
|---|---|
| Soluble | Able to dissolve in a solvent such as water. |
| Insoluble | Not able to dissolve in a solvent such as water. |
| Precipitate | An insoluble solid formed when two solutions react. |
| Precipitation reaction | A reaction in which two soluble compounds form an insoluble solid; also called double decomposition. |
| Sparingly soluble | Dissolves only to a very small extent, as calcium hydroxide does in limewater. |
Avoid these mistakes
1
Forgetting that every nitrate and every sodium, potassium and ammonium salt is soluble.
2
Listing lead(II) chloride as soluble because 'most chlorides are'; lead and silver are the exceptions.
3
Using titration to prepare an insoluble salt; those are made by precipitation.
4
Leaving out the state symbol (s) next to the precipitate in the equation.
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