Calcium hydroxide

 

Calcium hydroxide

Chemical formula	Ca(OH)2
OTP appearance	white solid
Molar Mass(g/mol)	74.093
Enthalpy of Formation(kJ/mol)	−987
Density(g/cc)	2.211
Melting Point(°C)	580 (decomp)
Solubility in water(g/L)	1.73
Solubility in ethanol(g/L)	non
NFPA 704	0 3 0
Thermal Decomposition	Calcium hydroxide 580°C CaO,H2O

Uses

Primary

• Feedstock for most hydroxides: sodium, potassium, etc
• Production of mortar and plaster

Secondary

• Whitewash

Natural Occurrence

• Calcium hydroxide does occur naturally as the rare mineral portlandite.

Hazards

• Calcium hydroxide is alkaline. It can irritate the skin, eyes and lungs and should not be ingested in large quantities. Wash with fresh clean water after contact.

Character

• Calcium hydroxide, calcium oxide, and calcium carbonate are three interconvertable calcium compounds.
  • Calcium hydroxide can be converted to calcium oxide by heating to 580°C, where it loses one molar equivalent of water equal to approximately 25% of its total mass.
  • Ca(OH)₂
    {

    →

    580°C}
    CaO + H₂O
  • Calcium hydroxide can be converted to calcium carbonate by bubbling carbon dioxide through a solution/suspension of calcium hydroxide
  • {{#Chem: Ca(OH)2(aq) + CO2 = CaCO3 + H2O))

Synthesis

From calcium oxide

In ideal conditions (distilled water, pure calcium oxide) this works. Presuming a "part by mass" is 1g, this yields half a mol (37g) of calcium hydroxide.

1. Gather a watertight container resistant to alkaline substances
2. Gather 9 parts by mass of water
3. Gather 28 parts by mass of calcium oxide
4. Place the water in the container
5. Slowly add the calcium oxide, allowing the water to cool in between additions

   CaO(s) + H₂O(l) → Ca(OH)₂ΔH=−63.7 kJ/mol of Calcium

6. The mixture is calcium hydroxide

Storage

• Calcium hydroxide is a caustic alkali, so glass and ceramic containers are excellent. Aluminum in particular is bad.
• Calcium hydroxide will absorb carbon dioxide from the air and precipitate as calcium carbonate, so keep in a sealed container