Aim
Make pure, dry crystals of a soluble salt from an insoluble base and an acid.
Method students should know
- Measure a fixed volume of the acid and pour it into a beaker.
- Warm the acid gently.
- Add the insoluble base in small masses.
- Continue adding until the base is in excess.
Variables
- Independent variable
- Mass of base added, or type of acid/base depending on investigation.
- Dependent variable
- Mass and quality of salt crystals produced.
- Control variables
- Volume and concentration of acid, Temperature, Evaporation time, Cooling conditions
Safety and common mistakes
- Wear eye protection because acids are irritants.
- Use gentle heating and keep the Bunsen flame controlled.
- Handle hot glassware with care.
- Adding too little base so acid remains in the final solution.
- Forgetting that copper sulfate is soluble and passes through the filter.
- Writing evaporate all the water instead of crystallise the solution.