Limewater is a clear, aqueous liquid known primarily for its use in scientific experiments and demonstrations. This substance is a solution created from a common compound derived from limestone, and it is frequently used in chemistry to identify a specific gas.
Chemical Composition and Nature
Limewater is chemically defined as a saturated aqueous solution of calcium hydroxide, which is an inorganic compound with the chemical formula Ca(OH)₂. This compound is more widely known by the traditional name slaked lime or sometimes hydrated lime. Since calcium hydroxide is only slightly soluble in water, the liquid quickly reaches its maximum saturation point. It is highly alkaline, having a pH of approximately 12.4, which classifies it as a strong base.
Simple Preparation Methods
The process of creating limewater begins with mixing calcium hydroxide powder (slaked lime) with water. Because the chemical has low solubility, only a small amount of the powder will dissolve, making it a saturated solution. The mixture must then be agitated to ensure that the maximum possible amount of the compound enters the solution. After agitation, the mixture is allowed to stand, typically for 24 hours, which permits the excess undissolved solid particles to settle. The clear liquid on top must then be carefully removed, either by decanting or filtering, to obtain a clean, usable solution.
The Defining Test for Carbon Dioxide
Limewater’s most recognized use in science is as a simple and effective test for the presence of carbon dioxide (CO₂) gas. When carbon dioxide is passed or bubbled through the clear limewater solution, the liquid turns distinctly cloudy or milky white. This visible change occurs because the dissolved calcium hydroxide reacts with the CO₂ to produce calcium carbonate (CaCO₃) and water. Calcium carbonate is insoluble in water, and the formation of a suspension of these tiny, white solid particles causes the characteristic milky appearance. This reaction is frequently used in classroom labs to confirm the production of carbon dioxide or to demonstrate the presence of CO₂ in exhaled human breath.
Historical and Practical Applications
Beyond its role as a chemical indicator, limewater has held various roles in industry and historical practice. Calcium hydroxide, the dissolved component of limewater, is a standard ingredient in preparing lime mortar, which is used in masonry, plaster, and cement for construction. The solution is also employed in industrial contexts as a neutralizing agent to treat acidic wastewater and as a flocculant to help remove minute particles during water purification. Historically, limewater was used in the culinary process known as nixtamalization, where maize is soaked to soften the kernels for grinding and to enhance the nutritional value of the grain. In art, the solution acts as a color solvent when applying pigments to wet plaster in the technique of buon fresco painting.