======Making Silicon From Sand======


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**Alternative titles:** Elemental Silicon from Silicon Dioxide
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====Summary====                   
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====Procedure====  
  - Measure a stoichiometric mixture of finely powdered magnesium and dry silicon dioxide, using a slight excess of silicon dioxide to suppress formation of magnesium silicide.  
  - In a refractory crucible with a fitted lid, gently preheat to minimize thermal shock.  
  - Add the powder mixture to the hot crucible, cover, and place in a furnace or strong flame until the reaction sustains and completes.  
  - Allow the crucible to cool behind a heat shield; do not open while hot.  
  - Break up the solid mass and transfer it to a beaker.  
  - Carefully add dilute hydrochloric acid in small portions to dissolve magnesium oxide and any unreacted magnesium; allow gases to escape safely.  
  - Decant and rinse repeatedly with water until neutral.  
  - Dry the remaining dark solid; this is crude elemental silicon powder.



====Links==== 
Silicon Synthesis (From Mg and Sand) - TheChemistryShack: 
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Silicon and silanes from sand - Royal Society of Chemistry: 
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====Variations====
  * Test electrical properties of the product by measuring resistance of a compacted pellet.



====Safety Precautions====
  * Conduct all heating steps in a fume hood or outdoors, wear eye protection, face shield, heat-resistant gloves, and a lab coat.  
  * Magnesium powder is highly flammable; keep away from ignition sources and do not use water on magnesium fires (use a Class D extinguisher or dry sand).  
  * The reduction is very exothermic and can spatter; use a lidded refractory crucible and a heat shield, and keep observers at a safe distance.  
  * Mixtures that form magnesium silicide can release silane and hydrogen on contact with acids or water; add acids slowly, in a fume hood, and vent gases safely.  
  * Dilute hydrochloric acid is corrosive; avoid skin and eye contact and neutralize spills promptly.
  * Allow the crucible to cool fully before handling to prevent burns and thermal shock fractures.  
  * Dispose of all chemicals according to institutional hazardous waste procedures; solid residues containing silicon and silica should be treated as chemical waste.





====Questions to Consider====
  * What is the balanced chemical equation for the main reduction? (2Mg + SiO2 → 2MgO + Si)  
  * Why is silicon dioxide used in slight excess in this procedure? (To minimize formation of magnesium silicide, Mg2Si, by consuming free magnesium.)  
  * How could you confirm that silicon formed rather than a mixture of unreacted sand and magnesium oxide? (Test solubility of MgO in acid, examine density differences, or analyze with conductivity or simple powder X-ray patterns if available.)  
  * What hazards arise if magnesium silicide forms and you add acid during the workup? (Mg2Si reacts with acids to generate silane and hydrogen, which are flammable and can ignite spontaneously.)