Production of Salts (OCR GCSE Combined Science A (Gateway)): Revision Note

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:

1. Add 50 cm³ dilute acid into a beaker and warm gently using a Bunsen burner - do not let it boil

2. 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)

3. Filter the mixture into an evaporating basin to remove the excess base

4. Gently heat the solution in a water bath or with an electric heater to evaporate the water and to make the solution saturated

5. Check the solution is saturated by dipping a cold glass rod into the solution and seeing if crystals form on the end

6. Leave the filtrate in a warm place to dry and crystallise, such as in a drying oven or the windowsill

7. 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