Question

Slaked lime whose solution is used for white-washing of walls is formed as a result of reaction between?
1. Calcium hydroxide and Water
2. Carbon dioxide (CO2) and Water
3. Methane and Water
4. Ethylene and Water

Answer 1

Correct Answer - Option 1 : Calcium hydroxide and Water

The correct answer is Calcium hydroxide and Water.

• Limewash
  • It is pure slaked lime in water.
  • It produces a unique surface glow due to the double refraction of calcite crystals.
  • When whitewash or limewash is initially applied, it has very low opacity, which can lead novices to over-thicken the paint.
  • The solution of the substance used for whitewashing is calcium oxide also called quicklime with the chemical formula CaO.
  • Quicklime is used for whitewashing as it produces calcium hydroxide (CaOH) when it reacts with water (H2O) and absorbs carbon dioxide (CO2) from the environment, as a result, it produces calcium carbonate (CaCO3) which creates a hard coating on the walls. Hence, Option 1 is correct.
  • It forms slacked lime or calcium hydroxide when the quick lime reacts with water CaO (s) + H2O (l) → Ca(OH)2(aq).
  • A solution of slaked lime is used for whitewashing walls.
  • Calcium hydroxide reacts slowly with the carbon dioxide in the air to form a thin layer of calcium carbonate on the walls.
  • Calcium carbonate is formed after two to three days of whitewashing and gives a shiny finish to the walls.
  • It is interesting to note that the chemical formula for marble is also CaCO3CaCO3.
  • Ca(OH)2(aq)Slaked lime+CO2(g)Carbon dioxide→CaCO3(s)Calcium carbonate+H2O(l)war.​​

• Chemical Compound Formulas

Compound name	Molecular weight	Molecular formula
Calcium hydroxide	74.092 g/mol	Ca(OH)2
Carbon dioxide	44.01 g/mol	CO2
Methane	16.043 g/mol	CH4
Ethylene	28.05 g/mol	C2H4