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Making salts and solubility
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Salts can be made in several ways. Which method you choose depends on whether the salt is soluble.
Soluble salts from insoluble bases
Add excess insoluble base (such as copper oxide) to warm acid until no more dissolves.
Filter off the excess. Evaporate some water and leave to crystallise.
Filter off the excess. Evaporate some water and leave to crystallise.
Soluble salts by titration
For an acid and a soluble alkali, use a titration to find the exact volumes, then mix those volumes without the indicator and crystallise.
Insoluble salts by precipitation
Mix two solutions; the insoluble salt forms as a precipitate. Filter, wash and dry it.
How would you make pure, dry crystals of copper sulfate?
- Add excess copper oxide to warm sulfuric acid.
- Filter off the unreacted copper oxide.
- Heat to evaporate some water, then leave to crystallise.
- Dry the crystals.
Answer: Excess base, filter, crystallise.
Soluble salts: excess insoluble base, filter, crystallise; or titration for alkalis. Insoluble salts: mix two solutions, filter the precipitate. Learn the solubility rules.
The interactive lesson includes the diagrams for this topic.
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