limewater

Limewater is an aqueous solution of calcium hydroxide (Ca(OH)2) in water. It is prepared by adding calcium hydroxide to water and allowing undissolved solids to settle; the clear liquid portion is used as limewater. It is a strongly alkaline solution, typically around pH 12.5, and may appear hazy if undissolved Ca(OH)2 is present. The term “milk of lime” is sometimes used for the suspension of Ca(OH)2 in water, while limewater usually refers to the clear solution.

Chemistry and reactions: Limewater reacts with acids to form corresponding calcium salts and water. A notable reaction is with carbon dioxide: Ca(OH)2 + CO2 → CaCO3 + H2O. The calcium carbonate produced is insoluble and forms a white precipitate, which causes the solution to become cloudy. This property is exploited in the limewater test for detecting carbon dioxide in gases or air.

Preparation and storage: To prepare limewater, a small amount of calcium hydroxide is stirred into water and the mixture is allowed to stand; the clear portion is decanted or filtered for use. Because limewater readily absorbs CO2 from the atmosphere, it should be stored in a tightly closed container and used relatively fresh for CO2 testing.

Uses: Limewater is used in chemistry and education to detect CO2, via the characteristic clouding upon CO2 exposure. It has historical and limited industrial uses in neutralization and regulation of alkalinity in water and soil contexts, though modern practices may employ other buffers and indicators.

Safety: Calcium hydroxide is caustic and can cause skin and eye irritation. Avoid inhalation of dust; handle with appropriate protective equipment and wash thoroughly after use.