Nathan Feifer
Son Francisco State College San Francisco, Cal~fornia94132
Studying the Chemical Properties of Metallic Aluminum
Metallic aluminum has a standard oxidation potential uf 1.67 v. Nevertheless, students rarely have an opportunity to ohserve its high degree of chemical activity in their experiments. The difficulty is occasioned by the thin, tough film of A1203that forms a protective coating over aluminum. Whenever unoxidized aluminum is exposed to air or water, the oxide forms immediately and halts the reaction between the aluminum and its chemical environment. There are several well-known exceptions to this' process: the thermit reaction is one; another is the reaction between aluminum and strong alkalies. The problem of studying the properties of aluminum in a wider number of simple reactions can be solved by the formation of an aluminum amalgam. This can be done readily by treating aluminum with mercurous nitrate. The following procedure is recommended for student experiments or for demonstrations by the teacher: (1) Obtain purified aluminum foil of ,001 in. thickness and cut it into about 50 squares of 1 in. X 1 in. (2) Place the aluminum squares into a beaker containing about 30 ml. of mercurous nitrate solution saturated a t room t e m ~ e r s r ture. (3) Heat the solution to boiling. Discontinue the boiling and stir vigorously for about 30 see. The foil will have turned gray as a result of the formation of the amalgam.
648
/
Journol o f Chemical Educofion
(4) Use tongs to remove the t~malgamatedaluminum squares and wash them thoroughly in cold water. (Students should be warned to w e tongs in handling the amalgamated ahminum strips.)
The followingreactions can then be observed using the washed amalgamated aluminum foil: (1) The amalgamated aluminum will react slowly with water a t room temperature liberating hydrogen visibly. (2) Amalgamated aluminum reacts more rapidly with hailing water: Place one amalgamated aluminum square in a. test tube. Add 5 ml of water and heat to boiling. The hydrogen liberated can be collected by water displacement and tested. (3) The amalgamated aluminum will react with s d t s of metds of lower oxidation potential and liberate the metals: Prepare O.lM solutions of the salts listed below. Place 10 ml of the solution to he tested in a 150 ml beaker and add the amalgamated aluminum strip. The metal in the solution is replaced quickly by the al~uninumand forms a deposit on the strip. The following salt solutions gave good results:
The foregoing experiments mny rwdily be included in all experimentr~lstudy denling with the electrochetnical series.
