Aluminum is an active metal, and a dense oxide film of about 50 angstrom (1 angstrom =0.1 nm) is immediately formed on the surface of aluminum in dry air, so that aluminum will not be further oxidized and can withstand water; But the aluminum powder, when mixed with air, burns violently and emits a blinding white flame; Molten aluminum can react violently with water; Aluminum is amphoteric, highly soluble in strong bases, but also soluble in dilute acids. It is insoluble in water, but can react slowly with hot water to produce aluminum hydroxide .