Aluminium by itself is a very reactive metal. However, aluminium is oxidized when exposed to air, forming a thin layer of protective aluminium oxide on its surface.

When some aluminium foil is added to a solution of copper(II) chloride in concentrated hydrochloric acid, the layer of aluminium oxide will be destroyed by chloride ions.

Al2O3 + 2Cl- + 3H2O → 2[Al(OH)2Cl] + 2OH-

The exposed aluminium metal reacts with hydrochloric acid, producing hydrogen gas.

2Al + 6H3O+ → 2Al3+ + 6H2O + 3H2

Hydrogen gas can be ignited.

The color of the flame is blue/green due to the presence of Cu2+ ions.

Hazards:
- Hydrochloric acid is very corrosive

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