|Al with Bromine|
Bromine is one of two liquid elements at room temperature (25°C), and is the only liquid nonmetal under normal conditions. It is a reddish-brown volatile liquid, highly toxic and corrosive, with a specific harsh smell. In regard to this, when handling bromine in an enclosed area make sure to use safety glasses as well as protective clothing; while experiment must be conducted in an efficient fume hood.
Aluminum is a metal and reacts violently with all halogen elements, including bromine. When aluminum foil is placed in the test tube containing some liquid bromine, a vigorous reaction occurs after a few seconds. Elemental Br2 is reduced in this electron transfer reaction, while aluminum is oxidized to form AlBr3 salt. Due to protective oxide coating on the aluminum, reaction does not start immediately. Once it starts generated heat causes some of the unreacted bromine to vaporize, but on the video presentation we can also observe white fumes of aluminum(III) bromide, all of these making the reaction impossible to do without proper ventilation. Generated heat also melts and ignites the aluminum foil which we observe as sparks at first, followed by a white blaze.
In reaction of aluminum with bromine aluminum(III) bromide is formed, following the chemical equation shown below:
As can be observed from the reaction enthalpy, the reaction is highly exothermic and a large amount of energy is released during the aluminum(III) bromide synthesis. However, the most common form of aluminum(III) bromide that exists at room temperature is Al2Br6, dimer, with a structural formula in which two Al ions share two Br ions, thus forming a tetrahedral molecule:
Gaseous molecules of Al2Br6 break up into AlBr3 monomers at high temperatures following the equation:
Pure aluminum(III) bromide is a highly hygroscopic white solid at standard conditions, absorbing moisture or water from the air and giving aluminum hydroxide and hydrogen bromide in the reaction: