Float
until you mix it
rubber
oil
Sink
yes
Shape the aluminum to look like a boat, so it displaces enough water to float. The force supporting the aluminum is the buoyant force. It is equal to the weight of the volume of water displaced.
Yes
the air inside the can keeps it afloat
Aluminum.
A thin aluminum foil can float on water if placed carefully flat on the surface because of the surface tension of water. If you were to submerge it, the foil will sink.
Generally speaking, a denser substance will sink in a less dense substance. Assuming standard temperatures, since aluminum has a density of about 2.7 grams per cubic centimeter and water only has 1 gram per cc, aluminum would sink. A thin aluminum foil could float by virtue of the surface tension on water (but if submerged, will sink). An aluminum boat would float because it displaces a greater mass of water than its own weight. An aluminum block could also float on a liquid of higher density.