Silane

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

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The Fresnel lens here was taken from an old overhead projector

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Quite a violent reaction, over in a few seconds

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Boiling tube cracked by the ferocity of the reaction

Experiment 2 – heating magnesium and silicon dioxide using a Fresnel lens

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Powdered magnesium and silicon dioxide

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Heat using the focussed rays of the sun

Experiment 3 – heating magnesium and silicon dioxide in a crucible using a Fresnel lens

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Adjust the lens to focus the suns rays onto the mixture

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An exothermic reaction, over in a flash

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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

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Experiment 5 – adding dilute hydrochloric acid to the product mixture

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The product mixture containing magnesium silicide

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Small, sputtering explosions

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Caught in the act

Experiment 6 – slow motion animation of adding dilute hydrochloric acid to the product mixture

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Slow motion

Links to movies on You Tube:

Experiment 1
Magnesium and silicon (IV) oxide reaction 1 – boiling tube / Fresnel lens
16 seconds

Experiment 2
Magnesium and silicon (IV) oxide reaction 2 – boiling tube / Fresnel lens
39 seconds

Experiment 3
Magnesium and silicon (IV) oxide reaction 3 -crucible / Fresnel lens
24 seconds

Experiment 4
Magnesium silicide and sulfuric acid – boiling tube
14 seconds

Experiment 5
Magnesium silicide and sulfuric acid 3 – watch glass in the dark
40 seconds

Experiment 6
Magnesium silicide and hydrochloric acid at 120fps, no sound (watch glass)
56 seconds