Magnesium silicide

Magnesium silicide, Mg2Si, is an inorganic compound consisting of magnesium and silicon. Silicon dioxide, SiO2, found in sand and glass, when heated with magnesium forms magnesium silicide. The first product in this reaction is silicon, which then reacts further with magnesium to produce Mg2Si:


 * SiO2 + 2Mg → 2MgO + Si


 * Si + 2Mg → Mg2Si

When magnesium silicide is placed into hydrochloric acid, HCl(aq), the gas silane, SiH4, is produced. This gas is the silicon analogue of methane, CH4, but is more reactive. Silane is pyrophoric, that is, due to the presence of oxygen, it spontaneously combusts in air:


 * Mg2Si(s) + 4HCl(aq) → SiH4(g) + 2MgCl2(s)


 * SiH4 + 2O2 → SiO2 + 2H2O

These reactions are typical of a Group 2 silicide. Mg2Si reacts similarly with sulfuric acid. Group 1 silicides are even more reactive. For example, sodium silicide, Na2Si, reacts rapidly with water to yield sodium silicate, Na2SiO3, and hydrogen gas.