Calcium oxide

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Calcium oxide
Chemical formula CaO
OTP appearance white solid 
Molar Mass(g/mol) 56.0774 
Melting Point(°C) 2613 
Boiling Point(°C) 2850 
Density(g/cc) 3.34
NFPA 704
NFPA704.png
0
3
2
 

Uses

Primary

Secondary

  • Heat without fire:
    CaO(s) + H2O(l) Ca(OH)2(aq) (ΔHr = −63.7 kJ/mol of CaO)

Natural occurrence

  • Does not occur naturally

Hazards

  • Corrosive to skin
  • Calcium oxide dust irritates the eyes and lungs
  • Mixed with water produces substantial heat as well as calcium hydroxide which is caustic.

Production

From calcium carbonate

  1. Place 100 units by mass of calcium carbonate in a lidded ceramic container
  2. Repeat
    1. Place the container in the lime kiln
    2. Heat to 900°C (orange heat) for 30 minutes
    3. Remove from fire and measure mass.
      N.B. You can use the weight loss to estimate total time to conversion: 100 → 90 is 10 units (out of 44) of mass removed. Estimate 2 hrs to convert all.
  3. until mass is 56-57 units.
    NB: The above presumes pure calcium carbonate as feedstock. Impurities may increase or decrease the target weight.
  4. The material is now mostly calcium oxide.

Purification

Testing

Storage

Calcium oxide decomposes when exposed to air along two routes:

CaO + CO2 CaCO3
CaO + H2O Ca(OH)2

Thus, storage is a problem. For these reasons, calcium oxide is most often used as quickly as it is produced.

Disposal

See Also

References