What is calcium hydroxide and how is it prepared?
Calcium hydroxide, chemical formula Ca(OH)2, commonly known as slaked lime or slaked lime, is a white solid that is slightly soluble in water. Its aqueous solution is often called limewater (in large quantities, it can form lime milk or lime slurry). It is strongly alkaline. It deteriorates by absorbing carbon dioxide and water in the air, and is often referred to as hygroscopic.
Common Reactions
Quicklime (calcium oxide) reacts with water to form calcium hydroxide. The chemical equation is: CaO + H2O -> Ca(OH)2
When heated to 512°C, the partial pressure of water and calcium hydroxide reaches 101 kPa (at atmospheric pressure), and calcium hydroxide decomposes into calcium oxide and water. The chemical equation is:
Ca(OH)2 -> CaO + H2O
Calcium hydroxide reacts with carbon dioxide to form calcium carbonate and water. The chemical equation is:
Ca(OH)2 + CO2 -> CaCO3 v + H2O.
This reaction is often used to test for carbon dioxide. A positive result is a milky white calcium hydroxide solution.
Calcium hydroxide reacts with sodium carbonate or sodium bicarbonate to produce sodium hydroxide and calcium carbonate. The chemical equation is:
Ca(OH)2 + Na2CO3 -> CaCO3v + 2NaOH)
2NaHCO3 + Ca(OH)2 -> CaCO3v + Na2CO3 + 2H2O (NaHCO3 in excess)
NaHCO3 + Ca(OH)2 -> CaCO3v + NaOH + H2O (Ca(OH)2 in excess). This reaction is used industrially to produce sodium hydroxide.
Preparation Method
Originated from the digestion of calcium oxide and water. CaO + H2O -> Ca(OH)2: Limestone is calcined to produce quicklime (calcium oxide) and then digested with water to produce calcium hydroxide. The slurry is purified, separated, and deslagging to produce the finished calcium hydroxide.
Health Effects
Excessive ingestion and absorption of calcium hydroxide by the human body can cause dangerous symptoms, including difficulty breathing, internal bleeding, low blood pressure, muscle paralysis, disruption of the myosin and actin systems, increased blood pH, and damage to internal organs.
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