Chemical A is used for water softening to remove temporary hardness. A reacts with sodium carbonate to generate caustic soda. When `CO_(2)` is bubbled through a solution of A, it turns cloudy. What is the chemical formula of A ?

Options

A. `CaCO_(3)`
B. `CaO`
C. `Ca(OH)_(2)`
D. `Ca(HCO_(3))_(2)`

Answer

To solve the problem, we need to identify the chemical A based on the clues provided in the question. Let's break it down step by step.

### Step 1: Understanding Temporary Hardness
Temporary hardness in water is primarily due to the presence of bicarbonates (like calcium bicarbonate). These can be removed by heating or by adding certain chemicals which convert them into insoluble carbonates.

**Hint:** Temporary hardness can be removed by converting soluble bicarbonates into insoluble carbonates.

### Step 2: Reaction with Sodium Carbonate
The question states that chemical A reacts with sodium carbonate (Na2CO3) to generate caustic soda (sodium hydroxide, NaOH).

We can write the reaction as:
\[ \text{A} + \text{Na}_2\text{CO}_3 \rightarrow \text{NaOH} + \text{CaCO}_3 \]

This indicates that A must be a compound that can react with sodium carbonate to produce sodium hydroxide and calcium carbonate.

**Hint:** Look for a compound that can release hydroxide ions when reacted with sodium carbonate.

### Step 3: Identifying Chemical A
From the options given:
1. CaCO3 (Calcium Carbonate)
2. CaO (Calcium Oxide)
3. Ca(OH)2 (Calcium Hydroxide)
4. Ca(HCO3)2 (Calcium Bicarbonate)

Among these, calcium hydroxide (Ca(OH)2) is known to react with sodium carbonate to produce sodium hydroxide and calcium carbonate.

**Hint:** Consider the properties of each compound and their reactions with sodium carbonate.

### Step 4: Reaction with CO2
The question also mentions that when CO2 is bubbled through a solution of A, it turns cloudy. This indicates the formation of an insoluble compound.

The reaction can be written as:
\[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]

The formation of calcium carbonate (CaCO3) is responsible for the cloudiness, as it precipitates out of the solution.

**Hint:** The cloudiness is due to the formation of an insoluble precipitate.

### Conclusion
Based on the above analysis, the chemical A is calcium hydroxide (Ca(OH)2), which is used for water softening and reacts with sodium carbonate to produce caustic soda and turns cloudy when CO2 is bubbled through it.

**Final Answer:** The chemical formula of A is \( \text{Ca(OH)}_2 \) (Calcium Hydroxide).