Preparing soluble and insoluble salts
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Explainer Video
Summary
Preparing soluble and insoluble salts
In a nutshell
Soluble salts can be made from insoluble oxides using a Bunsen burner and dilute acid. Dry hydrated copper sulfate will be formed during this practical. This will be achieved by adding an excess of copper oxide to sulfuric acid , filtering off the excess and then evaporating any water present.
Equations
The equation below is what happens to the acid and insoluble oxide in this experiment. Using this equation you should predict what salt will be formed.
Word equation | Symbol equation |
| | |
Equipment list
The following equipment list can be used to conduct an experiment to make salts.
Equipment | Use |
| Eye protection | To protect eyes from safety hazards |
| Beakers ( and ) | Container to hold sulfuric acid and copper sulfate solution |
| Spatula | Used in transfer of copper oxide powder to beaker |
| Glass rod | Used to stir sulfuric acid solution |
| Bunsen burner | Used to evaporate water from copper sulfate solution |
| Heat proof mat | Used to protect table from the heat generated by a Bunsen burner |
| Gauze | Placed on tripod to support evaporating basin |
| Tripod | Provides support to evaporating basin |
| Filter funnel | Provides support for filter paper in the filtration process |
| Filter paper | Placed in funnel to help filter excess copper oxide from solution |
| Evaporating basin | Copper sulfate solution stored |
| Dilute sulfuric acid | Used as sulfate source for copper sulfate crystals |
| Copper oxide powder | Used as copper source for copper sulfate crystals |
| Watch glass | Copper sulfate crystals placed here for final drying stage |
Experiment: Preparing copper sulfate crystals
Experiment variables
The independent variable is the one that you change. The dependent variable is the one which depends on what has been changed, therefore it is the one you measure. The control variable is the one which is kept constant
| Independent variable | . |
| Dependent variable | . |
| Control variable | . |
Safety precautions
When performing experiments, it is very important you consider safety precautions. This is so you and others do not get hurt.
Hazard | Risk | Safety Measure |
| Sulfuric acid | Concentrated acid is corrosive and damages skin and clothes | Use dilute acid |
| Sulfuric acid | Acid can irritate eyes | Wear safety goggles |
| Bunsen burner | Burns to skin | Do not touch apparatus |
| Bunsen burner | Hair or clothing catching fire | Tie long hair back and tuck in loose clothing |
Method
This is your instructions for how to complete the experiment.
 |
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| 1. | Add powdered copper oxide to sulfuric acid a level spatula at a time. After every time ensure to stir using a glass rod. Continue adding powder until powder does not dissolve anymore (unreacted powder visible in beaker). |
| 2. | Using filter paper and a funnel remove excess powder and collect the filtrate in the beaker. |
| 3. | Pour the copper sulfate solution from the beaker into the evaporating basin. |
| 4. | Set up the Bunsen burner, tripod and gauze for the evaporation of water. Get a member of staff to light the Bunsen burner when ready. |
| 5. | Place the evaporating basin on top of the gauze, ensuring the basin is directly above the Bunsen burner flame. |
| 6. | Turn off the Bunsen burner when all standing water is driven off. Leave evaporating basing for a few minutes to allow it to cool down to prevent burns. |
| 7. | Transfer crystals to watch glass and place in a warm dry place overnight for crystallisation to occur. Note: To get larger crystals it would be better to leave the crystals longer to crystallise with a little more water. |
Analysis
Note down the colour, size and dryness of your crystals.
Conclusion
Look at the size, colour and dryness of your crystals. What salt is formed in this experiment? To work out the salt you have made, look at the metal of the insoluble oxide / carbonate. Then look at the counter ion of the acid.
Evaluation
Once you have completed your experiment, it will be important to consider the quality of your crystals. If poor quality crystals were obtained, what could you have done better during the practical? What improvements could be made to the method and was the practical conducted in a safe manner?
FAQs - Frequently Asked Questions
How do I know when to turn off the Bunsen burner?
Turn off the Bunsen burner when all standing water is driven off. Leave evaporating basing for a few minutes to allow it to cool down to prevent burns.
How do I get larger crystals?
To get larger crystals it would be better to leave the crystals longer to crystallise with a little more water.
How do I know what salt I have made?
To work out the salt you have made, look at the metal of the insoluble oxide / carbonate. Then look at the counter ion of the acid.