During white-washing of walls, slaked lime reacts slowly with carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Which of the following reactions represents this correctly?

During the process of white-washing, a solution of slaked lime (calcium hydroxide) is applied to the walls. This calcium hydroxide reacts slowly with the carbon dioxide present in the air to form a thin, shiny layer of calcium carbonate. The chemical reaction is represented as Ca(OH)₂ (aq) + CO₂ (g) ⟶ CaCO₃ (s) + H₂O (l). In this reaction, calcium hydroxide is in an aqueous state (aq) as it is applied as a solution, carbon dioxide is a gas (g), and the resulting calcium carbonate is a solid (s) precipitate that provides the white finish, while water is released as a liquid (l). This reaction is also the basis for the lime water test, where the formation of insoluble calcium carbonate turns the solution milky [2].

Sources

1. [2] Science-Class VII . NCERT(Revised ed 2025) > Chapter 5: Changes Around Us: Physical and Chemical > Fig. 5.2: Blowing air in (a) tap water; (b) lime water > p. 61