Department of Chemistry and Biochemistry

Silane

Preparation of Silane

• Use a 1:2 mole ratio of sand to magnesium..

  SiO₂ = 60gm/mole

  Mg = 24gm/mole

• Use 5gm 60-200 mesh Silica gel, 4gm Mg powder, mix well in test tube.
• heat on big fat burner (Bunsen burner not hot enough). Heat from top end of rxn mix. Heating from the bottom of the test tube sends hot rxn mix flying across the room.
• After rxn completion, pour contents of test tube into beaker of 1M HCl. (Keep 6M HCl handy in case rxn is too slow).
• Mg₂Si sits on top of the solution, so stirring with a glass rod gives a better demo.

Notes
Using 60-200 mesh silica gel instead of sand makes the reaction very managable, takes much less heat to start, doesn't waste the test tube, and makes mostly Mg₂Si which makes more silane in weak HCl to generate nice little fires.

Reactions

2Mg + SiO₂ + heat --> Mg₂Si + O₂

Mg₂Si (s) + 4HCl (aq) --> SiH₄ (g) + 2MgCl₂ (aq)

SiH₄ (g) + 2O₂ (g) --> SiO₂ (s) + 2 H₂O

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Last Updated: 5/23/02