Silicon dioxide

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Silicon dioxide
aka Silica
Chemical formula SiO2
OTP appearance clear crystal 
Molar Mass(g/mol) 60.08 
Melting Point(°C) 1713 
Boiling Point(°C) 2950 
Density(g/cc) 2.648
NFPA 704
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Uses

  • Primary component of glass
  • Fused silicon dioxide is a high-temperature-resistant glass
  • Primary source of pure silicon

Natural occurrence

Silicon dioxide occurs naturally, usually as sand and other silacious minerals.

Hazards

  • GRAS

Production

Extraction

Purification

phase I

  1. grind to a fine powder, breaking the sand crystals along faults and exposing impurities on the surface
  2. Wash thoroughly with hot hydrochloric acid, converting calcium, magnesium, sodium, potassium, and iron compounds to water-soluble chlorides
  3. Wash thoroughly with hot water

Phase II

  1. melt N ubm of sodium hydroxide
  2. add M ubm of acid-and-water-washed sand
    2 NaOH(l) + SiO2(s) Na2SiO3 + H2O(v)
  3. heat and stir, producing a mixture of silcon dioxide, sodium hydroxide, and sodium silicate
  4. dissolve the mixture in water
  5. cool to room temperature
  6. filter
  7. discard residue (unreacted sand)
  8. heat and add hydrochloric acid until the solution is acidic
    Na2SiO3 + 2 HCl 2 NaCl + H2SiO3 // excess sodium hydroxide becomes salt and water
  9. cool to room temperature
  10. filter
  11. neutralize and discard filtrate
  12. retain residue (gel of silicic acid)
  13. wash with water
  14. heat silicic acid to produce pure silicon dioxide.
    H2SiO3
    {
    heat}
    SiO2(s) + H2O(v)

Purification

Testing

Storage

Disposal

Provided the crystals are coarse enough to fall out of the air, silicon dioxide can be disposed of into the environment.

See Also

References