Do magnesium, aluminium and zinc react with water?

1 Answer

Typically no, but magnesium can react slightly with cold water and more vigorously with hot water.


Under ordinary conditions, none of these reacts with water.

All three metals are above hydrogen in the activity series. Theoretically, they are all capable of displacing hydrogen from water, but that doesn't happen.

Clean magnesium ribbon has a slight reaction with cold water. After several minutes, bubbles of hydrogen slowly form on its surface.

The reaction soon stops because the magnesium hydroxide formed is almost insoluble in water. It forms a barrier on the magnesium surface and prevents further reaction.

#"Mg(s)" + "2H"_2"O(l)" → "Mg(OH)"_2"(s)" + "H"_2"(g)"#

The reaction of #"Mg"# is more noticeable in hot water (see how phenolphthalein indicator is used to detect the reaction in the video below).

Aluminium does not react with water, because it forms a tough protective layer of aluminium oxide, #"Al"_2"O"_3#, on its surface. That's why we use aluminium for cookware.

Zinc does not react with water, because it, too, forms a protective layer of insoluble zinc hydroxide, #"Zn(OH)"_2#.

#"Zn(s)" + "2H"_2"O(l)" → "Zn(OH)"_2"(s)" + "H"_2"(g)"#

The video below shows what happens when copper, zinc, and magnesium samples are placed in #"HCl"#, cold water, and hot water.