Properties of Calcium Hydroxide

Calcium hydroxide, also called slaked lime, is a colorless crystalline powder. It is obtained by wetting quicklime with water, a process called "slaking." Slaked lime is useful as a cheap alkali for removal of acid gases in, for example, coal gas purification and recovery of ammonia in the Solvay process. It is used as a suspension in water, such as milk of lime. Calcium hydroxide has applications in leather tanning to remove hairs from hides, and is also used in the manufacture of bleaching powder, glass, caustic soda, mortar and cement.

Physical Properties

Calcium hydroxide is an amorphous powder, sparingly soluble in water, about 0.2 g per 100 cubic cm. Hence, its solution is weakly basic. The solubility of calcium hydroxide in water decreases with increase in temperature of the solution. The suspension of slaked lime in water in commonly known as "milk of lime," while the clear solution is called "limewater."

Chemical Properties

When heated above 580 degrees C, slaked lime gets decomposed into oxides. When calcium hydroxide absorbs carbon dioxide from the air to produce calcium carbonate, the limewater turns milky. This property of calcium hydroxide is used to test a mixture of gases to determine the presence of carbon dioxide: when carbon dioxide is present, a thick precipitation of calcium carbonate will form if calcium hydroxide is shaken up in limewater in a clear jar. Limewater is a medium-strength base which reacts rigorously with acids. Limewater also reacts with many metals in the presence of water.

Solubility

The solubility of commercial limes in water does not fluctuate greater than seven percent as compared to that of pure calcium hydroxide. This variation is due to the fact that commercial limes contain traces of potassium and sodium hydroxide. The presence of carbonate, silica and magnesium does not influence the solubility of commercial limes, but they can affect its rate of solution. It is also important to note that particle size has an effect on its solubility.

Alkalizing Property

Calcium hydroxide compounds are available in both aqueous suspensions and solid forms such as cement, filled resins and liners. When these compounds are exposed to water, the calcium hydroxide disintegrates and behaves like a base.

Health Hazards

Calcium hydroxide can be hazardous to health if large amounts are inhaled or ingested. The victim may encounter the following symptoms: hypertension, an increase in blood acidity/alkaline ratio (which could harm internal organs), internal bleeding, skeletal muscle paralysis and difficulty breathing.

References

• Fact Monster
• National Center for Biotechnology Information
• Encyclopedia.com

Resources

• National Lime Association