Limewater

Limewater

HCl + Ca(CO3)2 expt

Dying Gaul (casting in Pushkin museum) 04 by shakko

Limewater is a clear, saturated aqueous solution of calcium hydroxide, Ca(OH)₂. It is traditionally used in the process of water purification, in the laboratory for the detection of carbon dioxide, and in the construction industry for plaster or mortar. Limewater reacts with carbon dioxide to form calcium carbonate, a process that is used to test for the presence of carbon dioxide in a gas sample.

Preparation

Limewater is prepared by dissolving calcium hydroxide (slaked lime) in water. The solution is prepared by adding calcium hydroxide to pure water and stirring until a saturated solution is formed. Excess calcium hydroxide settles at the bottom as a sediment. The clear solution is decanted and used as limewater. The solubility of calcium hydroxide in water is relatively low, so limewater is a weakly concentrated solution.

Chemical Properties

The primary chemical reaction involving limewater is its reaction with carbon dioxide (CO₂) to form calcium carbonate (CaCO₃) and water. This reaction is a basis for the limewater test for carbon dioxide, where the formation of a milky solution indicates the presence of CO₂.

\[ CO_2 + Ca(OH)_2 \rightarrow CaCO_3 + H_2O \]

This reaction is also reversible, which means that upon the addition of an excess of carbon dioxide, the calcium carbonate will dissolve, forming calcium bicarbonate, and making the solution clear again.

Uses

Water Purification

In water purification, limewater is used to remove impurities, such as sulfates and phosphates, from water. The process involves adding limewater to the water to be treated, which leads to the precipitation of these impurities as their respective calcium salts.

Carbon Dioxide Detection

In laboratories, limewater is a simple and effective reagent for testing the presence of carbon dioxide. The formation of a milky, white precipitate indicates a positive result for CO₂.

Construction

In the construction industry, limewater is used in making plaster and mortar. The calcium hydroxide in the limewater reacts with carbon dioxide in the air to form a hard, solid mass of calcium carbonate, which is an essential process in the setting of these materials.

Safety

Handling limewater requires basic safety precautions. While not highly corrosive, calcium hydroxide is a strong base and can cause irritation to the skin and eyes. Appropriate personal protective equipment (PPE), such as gloves and safety goggles, should be used when handling limewater.

See Also

• Calcium hydroxide
• Water purification
• Carbon dioxide