Which of the following salts has no water of crystallization ?

Question

Accepted Answer

Baking soda, which is sodium bicarbonate (NaHCO₃), is the correct answer as it does not have water of crystallization. Water of crystallization refers to the water molecules that are part of the crystalline structure of a compound. Baking soda is an anhydrous compound, meaning it does not contain any water molecules in its crystalline structure.

1. **Explanation for Option 4 (Baking soda):**
   - Baking soda is a simple compound that consists of sodium, hydrogen, carbon, and oxygen. It is commonly used in baking as a leavening agent. Unlike hydrates, baking soda does not incorporate water molecules into its crystal lattice. This lack of water of crystallization makes it distinct from the other options listed.

2. **Explanation for why other options are incorrect:**

- **Option 1 (Blue vitriol):**
     - Blue vitriol is another name for copper(II) sulfate pentahydrate (CuSO₄·5H₂O). It contains five molecules of water of crystallization, which are integral to its crystalline structure and give it the characteristic blue color. Therefore, it does have water of crystallization.

- **Option 2 (Washing soda):**
     - Washing soda is sodium carbonate decahydrate (Na₂CO₃·10H₂O). It contains ten molecules of water of crystallization. These water molecules are essential to its crystalline form, making it a hydrated compound.

- **Option 3 (Gypsum):**
     - Gypsum is calcium sulfate dihydrate (CaSO₄·2H₂O). It contains two molecules of water of crystallization. This water is part of its crystalline structure, which is why gypsum is classified as a hydrate.

In conclusion, baking soda is the only compound among the options that does not have water of crystallization, making Option 4 the correct choice.