To prepare a pure, dry sample of a soluble salt from an insoluble oxide or carbonate using a Bunsen burner and dilute acid.
A salt can be prepared and separated by acid-base neutralisation reaction.
- 1.0 mol/dm3 dilute sulfuric acid
- Copper (II) oxide powder
- Spatula & glass rod
- Measuring cylinder & 100cm3 beaker
- Bunsen burner
- Tripod, gauze & heatproof mat
- Filter funnel & paper, conical flask
- Evaporating basin and dish.
Diagram of the apparatus needed
The base is added in excess to use up all of the acid, which would become dangerously concentrated during the evaporation and crystallisation stages.
- Add 50cm3 dilute acid into a beaker and heat using a Bunsen burner flame.
- Add the insoluble oxide slowly to the hot dilute acid and stir until the base is in excess (i.e. until the base stops disappearing 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 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.
Hydrated copper(II) sulfate crystals should be bright blue and regularly shaped.
Describe how your crystals compare to the description in the results section. If different suggest an explanation.
Conclusion: Acid-base reactions produce salt and water with the regular shape of the salt reflecting the ionic lattice structure in its bonding.