Calcium oxide reacts with water, 2 of 3. A small amount of powdered solid calcium oxide (CaO, quicklime) is poured into a beaker with water. The water has few drops of universal indicator added. Initially the colour is green, indicating a neutral solution. Calcium hydroxide (Ca(OH)2, hydrated lime or caustic lime or slaked lime) is produced in the exothermic reaction: CaO + H2O -> Ca(OH)2. This process is known as slaking. Calcium hydroxide is poorly soluble in water. It still produces enough hydroxide ions to turn universal indicator blue, indicating an alkaline resulting solution.
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