定义Definition
氢氧化钙 Ca(OH)₂ 俗称熟石灰或消石灰，是白色粉末，微溶于水，其饱和溶液称石灰水。它由生石灰与水反应得到，是较强的碱，用于改良酸性土壤、配制砂浆和检验二氧化碳。
Calcium hydroxide, Ca(OH)₂, known as slaked or hydrated lime, is a white powder that is slightly soluble in water; its saturated solution is limewater. It is made by adding water to quicklime, is a fairly strong base, and is used to treat acidic soil, in mortar and to test for carbon dioxide.
检验二氧化碳Testing for carbon dioxide
CO₂ 通入石灰水生成白色 CaCO₃ 沉淀，溶液变浑浊：Ca(OH)₂ + CO₂ → CaCO₃ + H₂O；继续通入过量 CO₂，沉淀溶解：CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂。
CO₂ turns limewater milky by precipitating CaCO₃: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O; with excess CO₂ the precipitate dissolves again: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂.
溶解度随温度下降Solubility falls with temperature
与大多数固体不同，Ca(OH)₂ 的溶解度随温度升高而减小，20 °C 时约 1.7 g dm⁻³。
Unlike most solids, Ca(OH)₂ becomes less soluble as the temperature rises; at 20 °C its solubility is about 1.7 g dm⁻³.
用途Uses
撒入酸性土壤中和酸：Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O；砂浆在空气中吸收 CO₂ 生成 CaCO₃ 而硬化；也用于水处理和制漂白粉。
Spread on acidic soil it neutralises acid: Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O. Mortar hardens as it absorbs CO₂ from the air to form CaCO₃. It is also used in water treatment and to make bleaching powder.
化学性质Chemical properties
检验 CO₂：Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
Test for CO₂: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
与氯化铵共热放出氨：Ca(OH)₂ + 2NH₄Cl → CaCl₂ + 2NH₃ + 2H₂O
Releases ammonia when heated with ammonium chloride: Ca(OH)₂ + 2NH₄Cl → CaCl₂ + 2NH₃ + 2H₂O