Question

Write the name and chemical formula of bases present in lime water.

Answer 1

Hint: To answer this question, you must recall the composition of lime water. Pure lime water is a colorless and clear solution and has an alkaline bitter taste with a mild earthy smell. In the name lime water, lime does not refer to the citrus fruit lime but to the alkaline mineral found in the earth’s crust.

Complete step by step answer:
- We have heard and used the term lime water many times mostly during the detection of the presence of carbon dioxide in any reaction mixture with the carbon dioxide gas turning lime water milky. The milkiness is seen due to the formation of calcium carbonate in the solution which acts as a soluble white salt which dissolves and gives a milky white solution.
- From this we can conclude that lime water consists of a base of calcium. Lime water is the common name for a solution of calcium hydroxide in water. Calcium hydroxide is sparingly soluble in water at room temperature. It is a base and pure solution of lime water has a pH of around 12.
- Calcium is a group 2 metal of the modern periodic table. It has the atomic number 20 and has 2 valence electrons. It loses two electrons to form a divalent cation with a noble gas like stable electronic configuration.
- Meanwhile hydroxide ion is an anion carrying a single negative charge. Thus, to satisfy the valency and neutralize the charge on the carbon cation, there must be two hydroxide ions present in the molecule.

Thus, the chemical formula of Calcium hydroxide is given as $Ca{\left(OH\right)}_2$.

Note:
Lime water is generally prepared by mixing calcium hydroxide in water and removing the excess of undissolved salt. If excess of the solute is added, a milky solution is seen as a result of the homogenous suspension of the excess salt.