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calcium hydroxide, Ca(OH)2, colorless crystal or white powder. It is prepared by reacting calcium oxide (lime) with water, a process called slaking, and is also known as hydrated lime or slaked lime. When heated above 580°C it dehydrates, forming the oxide. Like the oxide, it has many uses, e.g., in liming soil, in sugar refining, and in preparing other compounds. It is a strong base and is widely used as an inexpensive alkali, often as a suspension in water (milk of lime); it is used in leather tanning to remove hair from hides. It is used in whitewash, mortar, and plaster. It is only slightly soluble in water, about 0.2 grams per 100 cubic centimeters, so its solutions are weakly basic. Limewater is a clear, saturated water solution of calcium hydroxide. It is used in medicine to treat acid burns and as an antacid. Because calcium hydroxide readily reacts with carbon dioxide, CO2, to form calcium carbonate, a mixture of gases can be tested for the presence of CO2 by shaking it with limewater in a clear container; if CO2 is present, a cloudy calcium carbonate precipitate will form.
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