Learning focus
Develop precise chemical language, connect equations and practical observations, interpret periodic trends and apply salt-preparation rules to unfamiliar examples.
Insoluble desired salt
Use precipitation. Mix two soluble solutions that provide the required cation and anion. The insoluble salt forms as a solid, which is filtered, washed and dried.
Soluble salt from an alkali
Use titration because acid and alkali are both soluble. Find the exact neutralising volumes using an indicator, then repeat without indicator and crystallise the pure solution.
Soluble salt from a solid reactant
If the second reactant is a suitable metal, insoluble base or insoluble carbonate, add it in excess to the acid. Excess solid ensures all acid reacts and can be removed by filtration.
Restrictions
The metal must be reactive enough to react safely with dilute acid; highly reactive metals are unsuitable. The acid must supply the required anion. A method that creates an insoluble product in the reaction vessel may not give the intended soluble salt solution.
Practical or data skill
For ten target salts, choose acid, second reactant and preparation method. Justify each choice in one sentence.
Examination tip
Start with: Is the desired salt soluble? Then ask whether the base is soluble.
Review questions and suggested answers
Question 1
How is an insoluble salt prepared?
Suggested answer
By precipitation.
Question 2
Why use titration with an alkali?
Suggested answer
Both reactants are soluble, so excess cannot be filtered away.
Question 3
Why add an insoluble reactant in excess?
Suggested answer
To use up all acid and allow excess to be filtered off.
