Practical: Prepare Copper(II)Sulfate
Aim
To prepare a pure, dry sample of hydrated copper(II) sulfate crystals
Materials
- 1.0 mol / dm3 dilute sulfuric acid
- Copper(II) oxide
- Spatula & glass rod
- Measuring cylinder & 100 cm3 beaker
- Bunsen burner
- Tripod, gauze & heatproof mat
- Filter funnel & paper, conical flask
- Evaporating basin and dish.
Diagram
Preparation of a soluble salt from an insoluble base and acid
The preparation of copper(II) sulfate by the insoluble base method
Method
- Add 50 cm3 dilute acid into a beaker and warm gently using a Bunsen burner
- Add the copper(II) oxide slowly to the hot dilute acid and stir until the base is in excess (i.e. until the base stops dissolving and a suspension of the base forms in the acid)
- Filter the mixture into an evaporating basin to remove the excess base
- Gently heat the solution in a water bath or with an electric heater to evaporate the water and to make the solution saturated
- Check the solution is saturated by dipping a cold glass rod into the solution and seeing if crystals form on the end
- Leave the filtrate in a warm place to dry and crystallise
- Decant excess solution and allow the crystals to dry
Practical Tip
- The base is added in excess to use up all of the acid, which would become dangerously concentrated during the evaporation and crystallisation stages
Results
- Hydrated copper(II) sulfate crystals should be bright blue and regularly shaped
Examiner Tip
Make sure you learn the names of all the laboratory apparatus used in the preparation of salts.