The chemical formula of soda ash is

Options

A. `Na_(2)CO_(3).10H_(2)O`
B. `Na_(2)CO_(3).2H_(2)O`
C. `Na_(2)CO_(3).H_(2)O`
D. `Na_(2)CO_(3)`

Explanation

To determine the chemical formula of soda ash, we need to analyze the options given and understand the properties of sodium carbonate.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question provides several options:
- Na2CO3.10H2O
- Na2CO3.2H2O
- Na2CO3.H2O
- Na2CO3

2. **Understand the Hydrates**:
- Na2CO3.10H2O is known as sodium carbonate decahydrate, which contains 10 water molecules.
- Na2CO3.2H2O is sodium carbonate dihydrate, containing 2 water molecules.
- Na2CO3.H2O is sodium carbonate monohydrate, containing 1 water molecule.
- Na2CO3 is anhydrous sodium carbonate, meaning it contains no water of crystallization.

3. **Heating the Hydrate**: When sodium carbonate decahydrate (Na2CO3.10H2O) is heated, the water of crystallization evaporates. As the heating continues, the number of water molecules decreases until all the water is removed.

4. **Final Product**: After complete evaporation of water, we are left with Na2CO3, which is the anhydrous form of sodium carbonate.

5. **Conclusion**: Therefore, the chemical formula of soda ash, which is the anhydrous form of sodium carbonate, is Na2CO3.

### Final Answer:
The chemical formula of soda ash is **Na2CO3**.

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