Reaction of Aluminum and Bromine
When bromine is introduced into a sealed reaction vessel containing pieces of aluminum foil, a dramatic reaction occurs. After an induction period of a couple of minutes, the reaction mixture begins to flash with yellow light and an orange cloud is produced. This demo is most effective when it is performed in a darkened room.
This reaction can be used as an example of a redox reaction and can be used to introduce the concept of ionic vs covalent bonding. It is also an example of an exothermic formation reaction that produces a lot of light, so it can be used to introduce the concepts of exothemicity and enthalpies of formation. You can use the attached PowerPoint slides to illustrate lattice energy using this reaction. Lastly, aluminum bromide is a Lewis acid and its fuming nature illustrates the reactivity of Lewis acids. Bromine is cool! Students love it. Allow about 10 minutes for this demo. More if you plan to use the ancillary materials.
2 Al(s) + 3 Br2(l) ==> 2 AlBr3(s)
Aluminum bromide is hygroscopic and fumes in air, forming a white cloud that looks orange because it is mixed with bromine vapor.1 Aluminum has a Pauling electronegativity of 1.5 and bromine has an electronegativity of 2.8.
1 Bassam Z. Shakashiri, Chemical Demonstrations, A Handbook for Teachers of Chemistry, v.1 (U. of Wisconsin, 1983) 69.
2 "Selected Values of Chemical
3 Division of Chemical Education, Inc., American Chemical Society, "Reaction of Aluminum With Bromine." Chemistry Comes Alive, 1999,
- 10 mL bromine
- a piece of aluminum foil, c. 5 cm x 5 cm, torn into small pieces
- reaction vessel
- vented addition funnel
- ring stand
- large ring
- clamp
- flask with ground glass neck
- 2 ground glass stoppers
- large plastic hose
- large trash bag
- rubber band
The addition funnel containing the bromine will be inserted in a flask to prevent the escape of vapors. Remove the addition funnel from the flask and insert it into the reaction vessel. Stopper the flask. Turn the stopcock on the addition funnel to allow the bromine to flow into the reaction vessel containing the aluminum foil pieces. Dim the lights in the room. After a few minutes, the reaction mixture will begin to flash and glow as the aluminum and bromine react.
Bromine is a strong oxidizing agent. Avoid contact with skin or eyes and avoid breathing vapors. If a bromine spill occurs, evacuate the students, contain the spill with sand, and quench the bromine with 5% sodium thiosulfate solution. The reaction products, which include aluminum bromide and hydrogen bromide, are also toxic and cause burns.
Assemble apparatus as shown in photograph with the aluminum foil pieces in the reaction vessel. Make sure that the hose is fitted tightly into the reaction vessel and that the trash bag is firmly affixed to the other end. The purpose of this device is to allow the vapors and air in the vessel to expand without escaping. Working under the vent hood, carefully pour about 10 mL of bromine into the vented addition funnel and stopper it. Wear gloves and goggles when handling bromine. It is extremely corrosive! Place the stoppered addition funnel containing the bromine in the Erlenmeyer flask with a ground glass neck and clamp the flask to the ring stand so that it cannot be overturned. When this demo is delivered, make sure that the sand container and the sodium thiosulfate solution container are on the cart in case of a bromine spill.
