Written by Rebecca Sunderman, Ph.D
Aluminum or Aluminium (to many outside the United States) is a critical component of many products we depend on. It is commonly used in the construction of siding, doors and window frames. As an alloy it is heavily used in the manufacture of boats, cars and airplanes. Many of the overhead electrical transmission lines and cable sheathings are made of aluminum and its alloys. One commonly recognized use for aluminum would be for beverage cans where 99% of all beer cans and 97% of all soda cans are made of aluminum. In the US, nearly half of the annual 1.8 million tons of aluminum containers are made from recycled aluminum. In manufacturing today, twenty-nine aluminum cans can be made from one pound of aluminum.
Unlike other materials used for packaging, the cost of collecting and recycling aluminum is less than the cost of producing new aluminum from ore. Making an aluminum can from recycled aluminum products requires approximately 5% as much energy as making an aluminum can from ore. Even though recycling aluminum is very cost effective, every three months Americans throw out enough aluminum to rebuild the entire U.S. commercial air fleet!
This experiment illustrates a chemical recovery method that can be used to recycle aluminum beverage cans. The aluminum is recovered as an alum. An alum is a hydrated double salt with two sulfate anions combined with two cations and twelve water molecules. The cations involved will be a M
+
cation and a M
3+
cation. The most common alums involve aluminum as the M
3+ cation. This is where the name alum originates.
M
+
M
3+
(SO
4
)
2
● 12 H
2
O
Many alums are known and they possess a wide variety of uses including: medical astringents, pickling agents (promotes crispness), water purification, fire extinguishers, hardening agents in plaster, affixing dyes to fabric and paper manufacturing.
The chemical synthesis of the potassium aluminum dodecahydrate, KAl(SO
4
)
2
● 12 H
2
O, is represented by the reactions shown below.
RXN # 1: 2 Al(s) + 2 KOH(aq) + 2 H
2
O(l) 2 KAlO
2
(aq) + 3 H
2
(g)
RXN # 2: 2 KAlO
2
(aq) + H
2
SO
4
(aq) + 2 H
2
O(l) 2 Al(OH)
3
(s) + K
2
SO
4
(aq)
RXN # 3: 2 Al(OH)
3
(s) + 3H
2
SO
4
(aq) Al
2
(SO
4
)
3
(aq) + 6 H
2
O(l)
RXN # 4: Al
2
(SO
4
)
3
(aq) + K
2
SO
4
(aq) + 24 H
2
O(l) 2 KAl(SO
4
)
2
● 12 H
2
O

Prelab Assignment: The following questions must be completed in your lab notebook prior to the start of lab. Be sure to write the question and your answer to the question.
1.
Look up the MSDS for potassium hydroxide. Describe the dangers of working with this material, the precautions you need to take, and any other safety information you deem significant.
2.
Locate and prepare a carbonated beverage container prior to lab time. Bring this clean and empty carbonated beverage can to lab. What can are you bringing?
3.
In the procedures you are asked to “mass out 1.00x grams” of the sandpapered aluminum scrap. What does the x mean? What balance should be used for this measurement?
4.
What is ddH
2
O?
5.
What is a theoretical yield and how would it be determined for this experiment?
Procedures and Data Collection : Be sure you are documenting procedure in the lab notebook.
Many of these procedural steps have vague numbers. You need to document the exact amounts of materials added, used, measured, etc. Qualitative descriptions of your observations are also essential to include in your lab notebook.
SAFETY CONCERN: POTASSIUM HYDROXIDE IS VERY CORROSIVE AND WILL
DISSOLVE CLOTHING AS WELL AS HUMAN SKIN.
Use sand paper to clean part of the surface of the aluminum can you brought to lab. Cut the aluminum into small pieces (A large surface area speeds of the dissolution process.) and mass out 1.00x grams.
Place the aluminum in a 250 mL beaker along with 34 mL of ddH
2
O and 15 mL of 6 M KOH.
Heat the contents of the beaker on a hot plate IN THE HOOD until all of the aluminum has dissolved. Remove the beaker from the hot plate and allow to cool to room temperature.
If any solids still remain in the beaker, set up a filter using glass wool in the mouth of a funnel to collect the filtrate solution. Use ddH
2
O, sparingly, to rinse the beaker and the glass wool to ensure complete transfer of the dissolved aluminum.
Add ten drops of methyl red indicator.(Methyl red is yellow in basic solutions and red in acidic solutions.) With vigorous stirring add, dropwise, 1.5 M H
2
SO
4
until the solution turns red. Heat the beaker with constant stirring until all of the precipitate dissolves. The solution should still maintain the red color. If it does not, add additional 1.5 M H
2
SO
4
as needed.
Cool the beaker in an ice bath for twenty minutes. Add 40 mL of isopropyl alcohol and stir for five minutes. Collect the crystals using vacuum filtration. Wash your crystals with 5mL of isopropyl alcohol. Water is soluble in isopropyl alcohol but the crystals are not.

Dry the crystals on a watch glass overnight in a drawer or for 15 minutes in an oven (45ºC).
Obtain the mass of alum crystals.
Data Analysis & Additional Questions: These questions can be completed outside of lab time.
Be sure to write the question and your answer to the question in your lab notebook.
1.
Why is it that bases are never stored in aluminum containers?
2.
Why does reaction # 1 need to take place in the hood?
3.
Write the net ionic equation for reaction # 2.
4.
From your observations, which two chemical reactions release heat (exothermic)?
5.
Calculate the theoretical yield for this experiment.
6.
Calculate the percent yield for this experiment.
7.
Aluminum is a reactive metal and when exposed to oxygen a thin layer of aluminum oxide forms. Aluminum oxide also reacts with potassium hydroxide to form the watersoluble potassium aluminate (KAlO
2
). Write a balanced chemical equation showing this side reaction. How does this side reaction affect your percent yield? Or does it?
References : http://www.epa.gov/wastes/conserve/materials/alum.htm
(accessed 2011) http://www.world-aluminium.org/About+Aluminium/Story+of (accessed 2011) http://www.world-aluminium.org/Sustainability/Recycling (accessed 2011) http://ntp-server.niehs.nih.gov/htdocs/Chem_Background/ExecSumm/aluminum (accessed 2003) http://www.genchemcorp.com/product/alum.shtml
(accessed 2003) http://www.co.ba.md.us/Agencies/publicworks/recycling/recylfact.html
(accessed 2003)