Aluminum
Formula: Al — Aluminum, aluminium
Appearance: Silvery-white lustrous metal
Hazard: Low hazard (solid) · Powder flammable
Properties
Density 2.70 g/cm³ — the lightest common structural metal. Melting point 660°C. Highly reactive thermodynamically (very negative reduction potential), but a thin, tough, self-repairing Al₂O₃ layer passivates the surface instantly in air, making it appear inert. Amphoteric — dissolves in both strong acids and strong bases. Cannot be electroplated from aqueous solution (the oxide reforms faster than plating can occur, and water is reduced preferentially). Available as foil, wire, or sheet.
Historical Context
Aluminum was more valuable than gold in the mid-19th century because isolating it was so difficult. Napoleon III reserved aluminum cutlery for honored guests while ordinary guests used gold and silver. The Hall–Héroult process (1886), which used electrolysis of molten alumina, suddenly made aluminum cheap and abundant — one of the greatest cost collapses in materials history.
Experiments
Amphoteric Reaction: Drop crumpled aluminum foil into sodium hydroxide solution — hydrogen bubbles steadily as aluminum dissolves in the base. Most metals react with acids; aluminum demonstrating base reactivity as well makes it a useful teaching example of amphoteric behavior.
Oxide Layer Demonstration: Polish aluminum foil with fine abrasive, then expose scratched areas to copper sulfate solution — copper deposits only where the oxide has been removed, revealing the protective role of the passive layer.
Experiments using this chemical:
- Electroplating - Why aluminum cannot be plated from aqueous solution
Safety
Aluminum foil and sheet are safe to handle. Aluminum powder is flammable — store away from ignition sources. Avoid contact with mercury, which destroys the oxide layer and causes rapid uncontrolled corrosion.