HCL in our stomachs helps digest food. As an acid, it donates an H+ ion (a proton) to the surrounding liquid. This ion grabs a-hold of a molecule willing to to donate an electron to it. The pH of a liquid is the measure of the -log of the molarity of the H+ in the solution. -Log([H+])=pH. Therefore, HCL is an acid. As an acid, it is a good solvent, and dissolves many things. This is why it is used as an industrial cleaner.
-
Blind people, clean excess mortar off brickwork, neutralize lye, anodize aluminum.
-
It's highly reactive; it will always lose the H+ and make Cl- as well. H+ and Cl- react with stuff in whatever it's in.