4CH1
Acids, Bases and Salt Preparations
Inorganic Chemistry
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 8% of your exam marks.
stable
Low
Stable8%
Soluble and insoluble salt preparation methods are consistently tested with multi-step answers.
Why solubility matters
- Knowing which salts dissolve in water and which do not decides which preparation method to use
- A soluble salt is built up in solution first and then crystallised out by evaporation
- An insoluble salt is dropped out of solution by precipitation — mixing two soluble salts whose ions exchange to form the wanted insoluble product
Solubility patterns to memorise
| Type of salt | Soluble in water | Insoluble exceptions |
|---|---|---|
| Sodium, potassium and ammonium salts | All | — |
| Nitrates | All | — |
| Chlorides | Most | Silver chloride, lead(II) chloride |
| Sulfates | Most | Barium sulfate, calcium sulfate, lead(II) sulfate |
| Carbonates | Sodium, potassium and ammonium carbonates only | The rest are insoluble |
| Hydroxides | Sodium, potassium and ammonium hydroxides; calcium hydroxide is sparingly soluble (limewater) | Most other metal hydroxides |
- Calcium hydroxide solution is what you know as limewater, used as the test for carbon dioxide