Learning focus
Develop precise chemical language, connect equations and practical observations, interpret periodic trends and apply salt-preparation rules to unfamiliar examples.
Suitable reactants
Use an insoluble metal oxide or hydroxide with the acid that supplies the desired anion. Copper(II) oxide with sulfuric acid is a common example for copper(II) sulfate.
Reaction conditions
Warm the acid to increase reaction rate, but do not boil. Add the insoluble base in small portions with stirring until some remains and no further reaction occurs. Excess solid confirms complete neutralisation.
Purification
Filter off unreacted base. The clear filtrate contains only the soluble salt and water if the method was successful. Concentrate and cool to crystallise.
Observations and colour
Black CuO disappears while acid remains and a blue copper(II) sulfate solution forms. Once acid is consumed, added CuO remains black. Observations should be described without assuming a colour for every metal compound.
Practical or data skill
Plan copper(II) sulfate preparation and explain the purpose of warming, excess solid and filtration.
Examination tip
The excess must be an insoluble solid so it can be filtered away.
Review questions and suggested answers
Question 1
Why warm the acid?
Suggested answer
To increase reaction rate.
Question 2
How do you know enough base has been added?
Suggested answer
Some remains unreacted after stirring.
Question 3
What is in the filtrate?
Suggested answer
The soluble salt solution.
