Solubility Rules (Edexcel GCSE Chemistry: Combined Science)

• 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

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