Production of a Pure Dry Sample of a Salt
The Preparation of Copper(II) Sulfate
Practical Skills Development
- Safe use of a range of equipment to purify and/or separate chemical mixtures including evaporation, filtration, crystallisation, chromatography and distillation
- Use of appropriate apparatus to make and record a range of measurements accurately, including mass, time, temperature, and volume of liquids and gases
- Use of appropriate apparatus and techniques for conducting and monitoring chemical reactions, including appropriate reagents and/or techniques for the measurement in different situations
- Safe use and careful handling of gases, liquids and solids, including careful mixing of reagents under controlled conditions, using appropriate apparatus to explore chemical changes and/or products
- Safe use of appropriate heating devices and techniques including use of a Bunsen burner and a water bath or electric heater
Aim
- To prepare a pure dry sample of copper(II) sulfate
Health & Safety Aspects
Hazard symbols to show substances that are corrosive, harmful to health and hazardous to the environment
- Safety glasses should be worn throughout the preparation
- Acids are corrosive and should be handled with care
- Copper(II) oxide and solid copper(II) sulfate can cause serious eye irritation and is a skin irritant. It is harmful if swallowed or inhaled and is toxic to aquatic life
- For all substances, avoid contact with the skin and use safety goggles
- For copper(II) oxide, care should be taken not to breathe in the powder
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.
The steps in the preparation of a soluble salt
Practical Tip:
- The base is added in excess to use up all of the acid, so that acidic fumes are not given off during the evaporation step
Method:
- Add 50 cm3 dilute acid into a beaker and warm gently using a Bunsen burner - do not let it boil
- Add the insoluble 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, such as in a drying oven or the windowsill
- Decant excess solution and allow the crystals to dry
Results:
- Hydrated copper(II) sulfate crystals should be bright blue and regularly shaped
Conclusion:
- Acid-base reactions produce salt and water with the regular shape of the salt reflecting the ionic lattice structure in its bonding
Examiner Tip
Make sure you learn the names of all the laboratory apparatus used in the preparation of salts.