Practical activity

Production of salts

There are a number of ways that you could produce salts in Chemistry. This is an outline of the required steps to undertake one of these methods.

It is important in this practical activity to safely use a Bunsen burner and a water bath. This includes the safe use of a range of equipment to separate and purify mixtures, including filtration and crystallisation.

Aims

To investigate the preparation of pure, dry hydrated copper sulfate crystals from copper oxide.

Method

Apparatus required for the core practical involving copper sulfate

The reaction

1. Add some dilute sulfuric acid to a small beaker.

2. Add some hot water from a kettle to larger beaker or water bath. Place the beaker of sulfuric acid into the hot water to warm up the acid.

3. Add a spatula of copper oxide powder to the acid and stir with a glass rod. Continue adding copper oxide powder until it is in excess.

Filtration

4. Fold a piece of filter paper and put it into a filter funnel. Fit the filter funnel into a conical flask.

5. Add the reaction mixture from the beaker to the filter paper.

6. Collect the filtrate, the copper sulfate solution. Do not collect the residue, the unreacted copper oxide.

7. Pour the filtrate into an evaporating basin.

Crystallisation

8. Set up a Bunsen burner, tripod and gauze on a heat resistant mat.

9. Put a beaker of water on the gauze and the evaporating basin on the beaker.

10. Heat the water, adjusting the Bunsen burner flame so the water is just simmering.

11. Stop heating before all the water in the evaporating basin leaves the copper sulfate solution.

12. Allow the evaporating basin to cool, then leave it aside for a few days or in a drying oven.

Results

Record the appearance of the copper sulfate crystals, including their colour and shape.

Analysis

Hydrated copper sulfate crystals should be blue and regularly shaped. Describe how your crystals compare to this description. Suggest an explanation for any differences.

Copper sulfate crystals
Copper sulfate crystals

Evaluation

Question

Explain why the sulfuric acid is warmed at step 2.

Warm acid will react faster than cold acid, helping to ensure that all the acid reacts with the copper oxide.

Question

Explain why an excess of the solid reactant is used at step 3.

This makes sure that all the acid has reacted. Filtering then removes the unreacted insolublereactant from the salt solution. As the acid is all used up and the insoluble reactant has been removed, this only leaves the salt and water. Therefore, evaporating the water leaves the pure salt.

Question

Describe how you could modify the method to make a pure, dry sample of an insoluble salt.

Mix together two suitable reactants. Use filtration to separate the precipitate as a residue from the solution. Wash the precipitate while it is in the filter funnel, with distilled water. This works because the precipitate is insoluble.

Hazards, risks and precautions

Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:

HazardPossible harmPossible precaution
Sulfuric acidConcentrated acid is corrosive and damages skin and clothesUse dilute sulfuric acid
Boiling water bathSkin burnsEnsure the boiling water bath is stable on the gauze
Hot copper sulfate solution spitting out during crystallisationDamage to eyes and skinWear eye protection and avoid standing over the hot apparatus