Diluted solution of mercury(II) chloride in contact with aluminum surface provides conditions for amazing phenomenon of relatively fast process of corrosion.

Materials

Aluminum piece (3 cm  x 3 cm x ~0.2 mm), A4 sheet of paper, sand paper, a piece of a wooden shish kebab stick, forceps.

Chemicals

Aqueous solution of mercury(II) chloride (40 mg in 10 mL water)

Experimental  

• Place the aluminum on the sheet of paper.
• Clean its surface with a send paper.
• Cut a piece of a wooden shish kebab stick with length of 2-3 cm.
• Take it with a forceps and soak one end with the solution of mercury(II) chloride.
• Touch the aluminum surface with the soaked stick end (Fig. 1), just to make gray stains on the surface.
• Watch what is happening.

Fig. 1. Contamination of the aluminum surface

Fig. 2. Corrosion of aluminum

At the place where the aluminum surface was contaminated with the mercury(II) chloride solution gray stain can be observed. In this case a chemical reaction produces aluminum alloy according to the following equation:
3HgCl₂(aq) + 2Al(s) = 3Hg(Al) + 2AlCl₃(aq)

This alloy provides conditions for oxidation of aluminum
Al(s) = Al³⁺ + 3e^–

One can observe a phenomenon of growing “sprouts” like mushrooms from the aluminum surface. They are most probably consisted of aluminum chloride, aluminum hydroxide, hydratised aluminum oxide and probably small amount of mercury.
The video is not real time record.

Safety tips

Avoid contact with the solution of mercury(II) chloride, it is toxic. In such a case wash the place with a lot of water.