Question

Write the method of preparation of Ca(OH)₂. What happens when CO₂ is passed through it? Write balanced chemical equation for the reaction involved.

Answer 1

• The method of preparation of calcium hydroxide Ca(OH)₂ involves adding water to calcium oxide (quick lime). When water is slowly added to calcium oxide, it reacts vigorously to produce slaked lime (calcium hydroxide), releasing a significant amount of heat in the process. The chemical equation for this reaction is:
  \[\ce{CaO(s) + H2O(l) -> Ca(OH)2(aq) + Heat}\]
• When carbon dioxide CO₂ is passed through a solution of calcium hydroxide, it reacts to form calcium carbonate CaCO₃ and water. This reaction is depicted by the equation:
  \[\ce{Ca(OH)2(aq) + CO2(g)->CaCO3(s) + H2O(l)}\]
• If an excess of carbon dioxide is passed through the mixture, it further reacts with the calcium carbonate to form calcium bicarbonate, which is soluble in water:
  \[\ce{CaCO3(s) + H2O(l) + CO2(g) -> Ca(HCO3)2(aq)}\]
• This sequence of reactions begins with a combination reaction to form calcium hydroxide, followed by a double displacement reaction upon the introduction of carbon dioxide, first leading to the precipitation of calcium carbonate and then, upon the introduction of more carbon dioxide, forming the soluble calcium bicarbonate. The compound that precipitates in the initial reaction with CO₂ is calcium carbonate CaCO₃ , and the ions present in it are Ca²⁺ and `"CO"_3^(2-).`