Question

A solution of substance ‘X’ is used for white washing. What is the substance ‘X’? State the chemical reaction of ‘X’ with water.

Updated on May 31, 2025 | By Learnzy Admin | 👁️ Views: 534 students

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Solution

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The substance ‘X’ is quicklime, also known as calcium oxide (CaO).

When calcium oxide is mixed with water, it reacts vigorously to form slaked lime, also known as calcium hydroxide [Ca(OH)₂]. This solution is used for whitewashing walls.

Chemical Reaction:

CaO (s) + H₂O (l) → Ca(OH)₂ (aq) + Heat

Calcium oxide (CaO) is quicklime.
Calcium hydroxide [Ca(OH)₂] is slaked lime (used in whitewashing).
The reaction is exothermic (produces heat).

Note: When this slaked lime solution is applied on walls, it reacts with carbon dioxide in the air to form a thin layer of calcium carbonate, which gives a shiny white finish.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

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