why does the bubble apear a few minutes later after putting aluminum sheet into diluted hydrochloric acid?
Aluminum element is extremely activated and will react with oxygen, generating aluminum oxide, once being exposed in air, so there is a layer of aluminum oxide on the surface of daily aluminum products including aluminum sheet. When aluminum sheet is put into diluted hydrochloric acid, aluminum oxide on the surface will firstly react with hydrochloric acid, generating aluminium chloride and water, the process won’t generate bubble, but after finishing the reaction of aluminum oxide on the surface, when the exposed aluminum element reacts with hydrochloric acid, generating aluminium chloride and oxygen, the bubble appears.
