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The saturated solution of calcium hydroxide is referred to as limewater. It should not be confused with the acidic fruit lime or with lemon water. In other words, limewater is a clear, colorless, aqueous solution of calcium hydroxide. It is made by mixing calcium hydroxide in water (4 to 8 times the quantity of lime). The term can be used to refer to water that contains dissolved lime or calcium salts.

The solubility of hydroxides in water increases as we go down the group. Calcium hydroxide is less soluble in comparison to barium hydroxide. 1 liter of pure water can dissolve about 1 gram of calcium hydroxide.

Properties
  • Limewater has an earthy smell
  • It tastes of calcium hydroxide (bitter).
Related Terms

Whitewash: A paint made from calcium hydroxide and chalk is known as whitewash. It is lime water used as a paint.

Milk of Lime: Calcium hydroxide is sparsely soluble in water. When excess of it is mixed with water, some of its particles remain suspended, imparting the solution a milky appearance. This mixture is known as milk of lime. It has a pH of 12.3

Making Lime Water

The method involves mixing distilled water with calcium hydroxide and shaking the mixture thoroughly, making a saturated solution of calcium hydroxide.

Materials
  • 1 teaspoon of calcium hydroxide (slaked lime)
  • ½ Jar of Water
Steps to Prepare
  • Pour in 1 teaspoon of slaked lime into a jar filled with water and place a cover on the jar.
  • Shake it thoroughly. At first, shake for a minute or two and then allow the mixture to stand for 24 hours.
  • After the given period, pour the solution into another container. Do not stir the sediments vigorously.
  • The clearer solution must be stored into a clean bottle or jar until its next use.
If excess calcium hydroxide is added, the solution has a milky appearance due to suspended calcium hydroxide particles.

Applications
  • Calcium hydroxide in lime water reacts with carbon dioxide to give calcium carbonate which forms an insoluble suspension in the solution. This property makes limewater useful in detecting the presence of carbon dioxide. A simple experiment that demonstrates this reaction is to exhale into limewater and observe the change in its color. The carbon dioxide breathed out reacts with calcium hydroxide to form calcium carbonate. And the solution becomes cloudy.
  • Waste containing sulfur dioxide is treated with limewater to remove the toxic sulfur dioxide from it. Calcium hydroxide in limewater reacts with sulfur dioxide to give calcium sulfite as a precipitate.
  • Lime water finds applications in cooking. In making tortillas, it is used for soaking maize. In the process, vitamin B and amino acid trytophan are liberated. Soaking in lime water also causes the kernels' skin to peel off.
  • Lime water is used as a color solvent in fresco painting. Painting is done on wet plaster with the use of pigments dissolved in limewater.
  • Organisms in reef tanks consume calcium from water. Limewater is added to the tanks to restore the lost calcium.