Passivity of Aluminum Submitted by: Leonard C . Grotz, University of Wisconsin Center, Waukesha, Wis. 53186 Checked by: William Dodd, Hiram College, Hiram, Ohio 44234 PREPARATION
A strip of Al sheet approximately 15 0,065 cm, 200 ml each of 0.5 M CuSO1, 6 M HN03, and 6 M HCI in 400-ml beakers, and distilled water in a wash bottle. DEMONSTRATION
Place the Al strip in the CuSO4 solution; no reaction occurs. Rinse the A1 strip with distilled water and place it in the HC1 solution. Leave the strip in the HCI for about one minute or until there is a very rapid evolution of hydrogen gas. Rinse the strip with distilled water and place it in the nitric acid solution for about two minutes. Remove, rinse, and place it in the CuS04 solution; as before, no reaction occurs. Rinse the strip and again place it in the HCI for about one minute. When there is a rapid evolution of hydrogen gas, quickly transfer the strip to the
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CuSOd solution. This time there is an immediate deposit of CU metal on the Al and a continued evolution of hydrogen gas' REMARKS
Aluminum metal is of sufficiently high chemical activity that it should reduce water and the ions of all other metals below it in the activity series. Many of the reactions do not occur, however, because of the oxide film on the Al surface that renders the metal "passive." This strongly adhering film is formed upon the reaction of Al with air, nitric acid, or water, but is destroyed by reaction with hydrochloric acid. After the oxide film has been removed from the surface of the Al, the Al metal reacts extremely rapidly with the copper ion and with water until the oxide film is restored.
