Soda Ash on Recrystallisation gives ........

Explanation

To solve the question "Soda Ash on Recrystallisation gives ........", we can follow these steps:

### Step 1: Understand what Soda Ash is
Soda ash is the common name for sodium carbonate (Na2CO3). It is often produced from the thermal decomposition of sodium bicarbonate (baking soda).

**Hint:** Remember that soda ash is sodium carbonate, which can be derived from sodium bicarbonate.

### Step 2: Know the process of obtaining Soda Ash
Soda ash can be obtained by heating sodium bicarbonate (baking soda). The reaction is as follows:
\[ 2 \text{NaHCO}_3 \xrightarrow{\text{heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \]
This reaction shows that when two moles of sodium bicarbonate are heated, they decompose to form sodium carbonate, water, and carbon dioxide.

**Hint:** Heating sodium bicarbonate leads to the formation of soda ash (sodium carbonate).

### Step 3: Understand the recrystallization process
Recrystallization is a purification technique that involves dissolving a solid in a suitable solvent and then allowing it to crystallize out. When soda ash is recrystallized, it can absorb water molecules from the environment.

**Hint:** Recrystallization helps in purifying the compound and can lead to the formation of hydrated forms.

### Step 4: Identify the hydrated form of Sodium Carbonate
When sodium carbonate is recrystallized, it can form a hydrated compound known as washing soda. The hydrated form of sodium carbonate is sodium carbonate decahydrate, represented as:
\[ \text{Na}_2\text{CO}_3 \cdot 10 \text{H}_2\text{O} \]

**Hint:** The hydrated form of sodium carbonate is commonly known as washing soda.

### Step 5: Conclusion
Thus, the answer to the question "Soda Ash on Recrystallisation gives ........" is:
**Washing Soda (Na2CO3·10H2O)**.

**Final Answer:** Soda Ash on recrystallisation gives washing soda.