Have you ever looked at the aluminum foil in your kitchen cabinet and wondered what cool experiments you could do with it? So have I! In this interesting experiment, we will be reacting copper sulfate with aluminum foil to make pure copper metal, in the form of copper powder. Whether you are in a school, or doing home chemistry, this experiment is sure to please.
Making Copper Powder – Background
The aluminum in aluminum foil reacts with copper sulfate and undergoes a single replacement reaction to create aluminum sulfate and copper metal:
2Al + 3CuSO4 → Al2(SO4)3 + 3Cu
This means that during the reaction, each aluminum atom loses three electrons to create an aluminum ion. Each copper ion gains two electrons, converting it into copper metal:
Al0 → Al3+ + 3 e–
Cu2+ + 2 e– → Cu0
Net ionic equation: 2Al0 + 3Cu2+ → 2Al3+ + 2Cu0
Aluminum foil is primarily made up of elemental aluminum arranged in a thin layer. However, it contains some iron and silicon as well, usually in the orders of 1% and 0.5%, respectively. Notably for this experiment, though, there is a passive layer of aluminum oxide on the surface of the foil, about 50-100 nanometers thick. This prevents the aluminum from being reactive upon contact. The chloride ions in the salt we add during the experiment will allow the copper ions to penetrate the oxide layer and react with the pure aluminum underneath.
Copper itself is a reddish-brown metal, but aqueous copper sulfate solution is a beautiful bright blue color. This is due to the coordination complex the Cu2+ ion forms with water—copper sulfate absorbs photons of light in the red region of the visible spectrum, thus transmitting blue light, making the solution appear blue. It absorbs this light because it is equivalent to the energy difference between the copper ion’s increased- and decreased-energy electron orbitals.
Materials
- Copper Sulfate (we used blue copper sulfate pentahydrate)
- Aluminum Foil
- Table Salt
- Warm Water
- Coffee Filter
- Funnel
- Glass Jar
- Magnetic Stirring Bar + Hot Plate (optional)
Note: approximately 13 times the amount of copper sulfate as aluminum should be used in order to guarantee a stoichiometric excess of aluminum and to maximize the amount of copper obtained. At least 4 times the amount of water as copper sulfate should be used in order for it to dissolve properly. In this experiment, we used 50 grams of copper sulfate, 4 grams of aluminum foil, and 400 mL of water.
Copper sulfate is sold at most hardware stores under the name “root killer”.
Copper Powder from Aluminum Foil – Procedure
1. Dissolve the copper sulfate in warm water
Place a magnetic stirring bar into the solution, and the beaker on a hot plate with magnetic stirring capabilities. The solution does not need to be heated, though, so be sure to use the appropriate setting on the plate. Otherwise, use a glass stirring rod to stir the solution and dissolve the copper sulfate. You may have to stir for several minutes for the crystals to dissolve completely.
2. Add the aluminum foil into the copper sulfate solution
You may need to scrunch or poke at it in order to ensure that all of the foil gets submerged.
3. At this point, the reaction does not occur spontaneously.
This is because of the aluminum oxide layer discussed earlier, which acts as an impenetrable barrier between the reactive aluminum metal and the copper ions. This oxide layer is called a passivation layer. This is the reason that aluminum foil is generally inactive, even though aluminum itself is a very active metal.
4. Add table salt to the solution, about ¼ teaspoon.
This allows the copper ions to bypass the aluminum oxide layer, and the reaction proceeds as expected. At this point, you should observe a small amount of hydrogen gas bubbling out of the solution. This is due to a side reaction between the reactive aluminum and the water that reaches it alongside the copper ions: 2Al + 3H2O → Al2O3 + 3H2 . The solution should also heat up significantly, as the reaction between the aluminum and copper ions is exothermic.
5. Allow the reaction to proceed.
Reddish-brown copper metal should begin to appear on the surfaces of the aluminum foil and sink to the bottom of the beaker. When the blue copper sulfate solution loses all of its color and appears clear, the reaction has gone to completion with regard to copper. It may also take on a reddish-brown hue due to the fine copper metal suspended in it. There should be a small amount of aluminum foil remaining, as it was in excess. To test if the reaction has truly gone to completion, place a small amount of new aluminum foil into the beaker, and watch it carefully to see if any copper forms on it.
6. Filter the solution.
Be sure to remove any remaining aluminum foil first using tweezers. For this experiment, gravity filtration works very well. Place the coffee filter in the funnel, positioned on top of the glass jar. Pour the solution and copper metal powder into the filter paper. Allow it to drip through, leaving only the copper. Wash the copper with distilled water while it is still in the filter to remove any remaining aluminum sulfate or salt, then dry it. The filtered solution should appear clear, but it may still look reddish if there are copper particles too fine to be filtered out remaining suspended in it.
7. Scoop it out
The copper powder may be too heavy to be poured out onto the filter with the rest of the liquid. In this case, simply scoop it out with a plastic utensil, and wash and dry as above. And that’s it – we made copper powder from aluminum foil!
Safety
Note that copper sulfate is somewhat toxic, however, the lethal dose in adults is quite high, about 25 grams. Avoid ingesting or inhaling the chemical; we recommend wearing goggles and gloves as it may cause irritation. If you do come into contact with it, simply wash your hands thoroughly.
Store the copper powder for future experiments, or disposed of it in the trash if needed. Pour the remaining, filtered solution containing aluminum sulfate down the drain with plenty of water.
Further Experiments
Click here to see what other interesting experiments can be done using copper sulfate! Be sure to also check out these similar experiments to see the elephant toothpaste experiment, and to find out how to extract potassium metal from a banana and how to create tin crystals in tin chloride solution! Younger kids can also make an aluminum foil boat.