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 $(CuO)$ to sulfuric acid $(H_2SO_4)$ , 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
$copper\ oxide\ +\ sulfuric\ acid\rightarrow\ copper\ sulfate\ +\ water$	$CuO(s)\ +\ H_2SO_4(aq)\ \rightarrow\ CuSO_4(aq)\ +\ H_2O(l)$

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 ( $250 \, cm^3$ and $100 \, cm^3$ )	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	$Amount\ of\ water\ present\ in\ evaporating\ basin$ .
Dependent variable	$Purity\ and\ dryness\ of\ copper\ sulfate\ crystals$ .
Control variable	$Volume\ of\ sulfuric\ acid$ .

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.

Chemistry; Chemistry practicals; KS4 Year 10; Preparing soluble and insoluble salts

1.	Spatula
2.	$CaO\ / \ CaOH$ powder
3.	Dilute $H_2SO_4$ solution
4.	Filtering off excess $CaO\ / \ CaOH$
5.	Copper sulfate solution
6.	Copper sulfate crystals forming in an evaporating dish.

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 $100\,cm^3$ 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.

$copper\ oxide\ +\ sulfuric\ acid\rightarrow\ copper\ sulfate\ +\ water \newline \ \newline CuO(s)\ +\ H_2SO_4(aq)\ \rightarrow\ CuSO_4(s)\ +\ H_2O(l)$

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?