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An acid will react with metal oxides.

In this reaction, we are going to use sulfuric acid and copper(II) oxide. This time there will be no gas produced. However, there will be other evidence that a chemical reaction is taking place.

Apparatus and chemicals

• Kettle
• 250 cm³ beaker
• 100 cm³ beaker
• Measuring cylinder
• Spatula, watch glass, glass rod
• Heatproof mat
• Safety goggles
• Sulfuric acid 0.5 mol/dm³
• Copper(II) oxide (2 g)
• pH paper

Method

1. Using pH paper determine the pH of the acid at the start, record this in your results.
2. Using a measuring cylinder, measure out 25 cm³ of sulfuric acid into the small beaker.
3. Collect approximately 2 g of copper(II) oxide on a watch glass.
4. Using hot water from a kettle, fill 1/3 of the larger beaker with hot water.
5. Warm the sulfuric acid beaker by letting it rest (carefully) in the hot water bath (leave for 2 min).
6. Carefully remove the small beaker and add copper(II) oxide to the acid slowly, stir with a glass rod.
7. Keep adding the copper(II) oxide, until there is some left over at the bottom of the beaker. Let the beaker sit for 2 min to allow the black powder to settle.

Observations

In this experiment, you should be able to observe that at the start the acid has a pH of about 1-2. Also, although there is no gas produced, there is a chemical reaction taking place as the solution changes from colourless to a pale blue, you should also notice that the copper(II) oxide disappears at the start.

However, once all the acid has reacted, the copper(II) oxide remains behind as seen by black powder at the bottom of the beaker. The blue colour is due to the formation of a soluble salt.