When comparing how magnesium and aluminum react with hydrochloric acid (HCl), magnesium reacts more rapidly than aluminum. This can be attributed to the differences in their reactivity and the protective oxide layer that aluminum forms.
Magnesium is a highly reactive metal that readily reacts with acids to produce hydrogen gas and a corresponding salt. The reaction can be represented as:
Mg + 2HCl → MgCl2 + H2
This reaction is vigorous and can produce hydrogen bubbles quickly.
Aluminum, while also a reactive metal, has a significant factor affecting its reactivity: a thin oxide layer of aluminum oxide (Al2O3) forms on its surface when exposed to air. This oxide layer acts as a barrier that inhibits further reaction with acids like HCl unless it is disrupted. For aluminum to react with HCl, this oxide layer must be removed, which makes the reaction slower compared to magnesium.
In summary, magnesium reacts rapidly with HCl due to its high reactivity and lack of a protective oxide layer, whereas aluminum’s oxide layer slows down its reaction rate.