Silane is toxic and all reactions involving magnesium silicide to produce silane should be carried out in a fume cupboard.
In the August 2016 blog we looked at the reaction of magnesium with oxygen and chlorine.
Magnesium is so reactive it will take the oxygen away from silicon in sand, (silicon dioxide, SiO2) .
Magnesium reacts with sand to produce magnesium oxide and silicon.
2Mg + SiO2 -> 2MgO + Si
If an excess of magnesium is used, magnesium silicide (Mg2Si) is also formed.
2Mg + Si -> Mg2Si
Silane is produced when magnesium silicide is reacted with dilute acids, such as hydrochloric and sulfuric acids, to produce silane.
For example, 4HCl + Mg2Si -> SiH4 + 2MgCl2
Silane bursts into flames as soon as it is produced.
For example, SiH4 + 2O2 -> SiO2 + 2H2O
Experiment 1 – heating magnesium and silicon dioxide using a Fresnel lens
The Fresnel lens here was taken from an old overhead projector
Quite a violent reaction, over in a few seconds
Boiling tube cracked by the ferocity of the reaction
Experiment 2 – heating magnesium and silicon dioxide using a Fresnel lens
Powdered magnesium and silicon dioxide
Heat using the focussed rays of the sun
Experiment 3 – heating magnesium and silicon dioxide in a crucible using a Fresnel lens
Adjust the lens to focus the suns rays onto the mixture
An exothermic reaction, over in a flash
The product mixture contains magnesium silicide which must be left to cool for several minutes
Experiment 4 – adding dilute sulfuric acid to the product in a boiling tube
Experiment 5 – adding dilute hydrochloric acid to the product mixture
The product mixture containing magnesium silicide
Small, sputtering explosions
Caught in the act
Experiment 6 – slow motion animation of adding dilute hydrochloric acid to the product mixture
Links to movies on You Tube:
Magnesium and silicon (IV) oxide reaction 1 – boiling tube / Fresnel lens
Magnesium and silicon (IV) oxide reaction 2 – boiling tube / Fresnel lens
Magnesium and silicon (IV) oxide reaction 3 -crucible / Fresnel lens
Magnesium silicide and sulfuric acid – boiling tube
Magnesium silicide and sulfuric acid 3 – watch glass in the dark
Magnesium silicide and hydrochloric acid at 120fps, no sound (watch glass)