Question

Which of the following is formed after a few days of whitewashing and gives a shiny finish to the wall?

• A. Calcium hydroxide
• B. Calcium carbonate
• C. Calcium oxide
• D. Calcium nitrate

Hint:

The chemical pathway of lime products:
1. CaO (Quicklime) + \(\text{H}_2\text{O} \to \text{Ca(OH)}_2\) (Slaked lime, used for whitewash).
2. \(\text{Ca(OH)}_2\) + \(\text{CO}_2 \to \text{CaCO}_3\) (Calcium carbonate, gives the shiny wall).

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the chemical compound that is slowly formed on walls over a period of two to three days after whitewashing, which is responsible for giving the walls a shiny, bright appearance.

Step 2: Key Formula or Approach:
We analyze the chemical reaction between slaked lime (calcium hydroxide) and atmospheric carbon dioxide.

Step 3: Detailed Explanation:

• During whitewashing, a suspension of slaked lime, which is calcium hydroxide [\(\text{Ca(OH)}_2\)], is applied to the walls.

• Once applied, calcium hydroxide reacts slowly with carbon dioxide (\(\text{CO}_2\)) present in the surrounding air.

• This reaction leads to the slow formation of a thin, hard, and uniform layer of calcium carbonate (\(\text{CaCO}_3\)) on the surface of the walls over a period of two to three days:
\[ \text{Ca(OH)}_2\text{(aq)} + \text{CO}_2\text{(g)} \to \text{CaCO}_3\text{(s)} + \text{H}_2\text{O(l)} \] - This thin layer of calcium carbonate has crystalline properties that reflect light well, giving a shiny, white finish to the walls.


Step 4: Final Answer:
The compound formed is calcium carbonate.