Silane

Materials

Cart with Safety Shield

25 x 200 Test Tube (with Mg and SiO₂ mixture)

Long Handled Test Tube Holder

Small Safety Shield

Large Bunsen Burner with Long Hose

600 mL Beaker

Long Glass Stir Rod

Bottle of 1M Hydrochloric Acid

Gloves and Goggles

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.

Procedure

Heat the test tube slowly on a big fat burner (A regular bunsen burner is not hot enough). Heat from the 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 the reaction 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

Waste Management

Let the beaker with the silane sit labeled in a fume hood till everything has reacted. Put the Test Tube in the beaker to let any left over silane react. The test tube can be thrown away in the broken glass container and everything else can be neutralized and poured down the sink.