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Solubility Rules (Edexcel GCSE Chemistry: Combined Science)
Revision Note
Solubility Rules
- Ionic compounds are generally soluble in water compared to covalent substances, but there are exceptions
- A knowledge of the solubility of ionic compounds helps us to determine the most appropriate method for the preparation of salts
- The solubility of common ionic compounds is shown below:
Solubility of Ionic Compounds Table
- Calcium hydroxide is slightly soluble in water
Examiner Tip
Calcium hydroxide solution is more commonly know as limewater and is used to test for carbon dioxide.
Predicting Precipitates
- Some salts can be extracted by mining but others need to be prepared in the laboratory
- How the salt is made in the laboratory depends on whether the salt being formed is soluble or insoluble in water
- To do this the balanced equation is written down to determine the identify of the salt product
- Then check the solubility of the salt using the solubility table
- If it is soluble in water, then it can be prepared by titration
- If it is insoluble then it can be prepared by precipitation
- For example a silver nitrate solution is mixed with a sodium chloride solution:
AgNO3 (aq) + NaCl (aq) ⟶ AgCl (s) + NaNO3 (aq)
- From the table both AgNO3 and NaCl are water soluble but AgCl, silver chloride, is not and hence forms a precipitate
Examiner Tip
The precipitation reaction by combining two soluble salts is also known as a double decomposition or double displacement reaction.
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