**Crystals of Washing Soda and Air Exposure**

When crystals of washing soda (sodium carbonate decahydrate) are exposed to air, several changes occur due to the hygroscopic nature of the compound. Here's a detailed explanation of what happens when washing soda crystals come into contact with the air:

**1. Absorption of Moisture:**
- Washing soda crystals readily absorb moisture from the air due to their hygroscopic nature.
- The primary component of washing soda, sodium carbonate, has a strong affinity for water molecules.
- As a result, the exposed crystals attract and absorb water vapor from the surrounding environment.

**2. Formation of Sodium Carbonate Monohydrate:**
- The absorbed water molecules react with sodium carbonate, leading to the formation of sodium carbonate monohydrate (Na2CO3·H2O).
- This hydrated form of washing soda is characterized by a single water molecule bound to each sodium carbonate molecule.

**3. Loss of Crystal Structure:**
- As the washing soda crystals absorb moisture and transform into sodium carbonate monohydrate, their crystal structure may undergo changes.
- The once solid and compact crystal lattice may become more fragile and prone to disintegration.

**4. Formation of Efflorescence:**
- If the humidity levels in the surrounding air decrease, the excess water absorbed by the washing soda crystals will start to evaporate.
- During evaporation, the water molecules carrying sodium carbonate monohydrate may migrate to the crystal's surface.
- As the water evaporates, it leaves behind a powdery white residue known as efflorescence.
- Efflorescence is composed of sodium carbonate monohydrate crystals that have been deposited on the surface of the washing soda crystals.

**5. Decreased Solubility:**
- Sodium carbonate monohydrate has slightly lower solubility in water compared to the anhydrous form of washing soda.
- Therefore, when washing soda crystals are exposed to air and transform into the hydrated form, their solubility in water may decrease slightly.

In summary, when crystals of washing soda are exposed to air, they absorb moisture, undergo a chemical transformation into sodium carbonate monohydrate, may experience changes in their crystal structure, and may exhibit efflorescence on their surface. These changes do not significantly affect the chemical properties of washing soda, but they alter its physical characteristics and solubility to some extent.

When crystals of washing soda are exposed to air Sodium Carbonate will be formed as it loses water of crystallisation