What is the action of heat on the following compound?
i.Na2CO3
and CaCO3
​
ii.MgCl2.6H2O
and CaCl2.6H2O

iii.Ca(NO3)2
and NaNO2

Let's go through each compound and discuss the action of heat on them:

### i. Sodium Carbonate (Na₂CO₃) and Calcium Carbonate (CaCO₃)

1. **Sodium Carbonate (Na₂CO₃)**:
- When heated, sodium carbonate does not decompose significantly. However, at very high temperatures, it can undergo a process called thermal dissociation to give sodium oxide (Na₂O) and carbon dioxide (CO₂):
\[
\text{Na}_2\text{CO}_3 (s) \rightarrow \text{Na}_2\text{O} (s) + \text{CO}_2 (g)
\]
- In practical terms, sodium carbonate remains stable under normal heating conditions.

2. **Calcium Carbonate (CaCO₃)**:
- Upon heating, calcium carbonate decomposes to form calcium oxide (CaO) and carbon dioxide (CO₂):
\[
\text{CaCO}_3 (s) \rightarrow \text{CaO} (s) + \text{CO}_2 (g)
\]
- This reaction occurs at around 900 °C to 1000 °C and is an important step in the production of lime.

### ii. Magnesium Chloride Hexahydrate (MgCl₂·6H₂O) and Calcium Chloride Hexahydrate (CaCl₂·6H₂O)

1. **Magnesium Chloride Hexahydrate (MgCl₂·6H₂O)**:
- When heated, magnesium chloride hexahydrate loses its water of crystallization and forms anhydrous magnesium chloride (MgCl₂) and water vapor:
\[
\text{MgCl}_2 \cdot 6\text{H}_2\text{O} (s) \rightarrow \text{MgCl}_2 (s) + 6\text{H}_2\text{O} (g)
\]
- This process begins at around 100 °C and is complete by about 200 °C.

2. **Calcium Chloride Hexahydrate (CaCl₂·6H₂O)**:
- Similar to magnesium chloride, calcium chloride hexahydrate loses its water of crystallization upon heating:
\[
\text{CaCl}_2 \cdot 6\text{H}_2\text{O} (s) \rightarrow \text{CaCl}_2 (s) + 6\text{H}_2\text{O} (g)
\]
- This occurs at temperatures above 100 °C, producing anhydrous calcium chloride.

### iii. Calcium Nitrate (Ca(NO₃)₂) and Sodium Nitrite (NaNO₂)

1. **Calcium Nitrate (Ca(NO₃)₂)**:
- When heated, calcium nitrate decomposes to form calcium oxide (CaO), nitrogen dioxide (NO₂), and oxygen (O₂):
\[
2\text{Ca(NO}_3\text{)}_2 (s) \rightarrow 2\text{CaO} (s) + 4\text{NO}_2 (g) + \text{O}_2 (g)
\]
- This reaction typically occurs at temperatures above 600 °C.

2. **Sodium Nitrite (NaNO₂)**:
- Upon heating, sodium nitrite decomposes to produce sodium nitrate (NaNO₃) and nitrogen oxide (NO) or nitrogen dioxide (NO₂), depending on the conditions:
\[
2\text{NaNO}_2 (s) \rightarrow \text{Na}_2\text{O} (s) + \text{NO} (g) + \text{O}_2 (g)
\]
- This reaction can also produce nitrogen dioxide when further oxidized.

### Summary
- **Na₂CO₃** remains stable under heat.
- **CaCO₃** decomposes to CaO and CO₂.
- **MgCl₂·6H₂O** and **CaCl₂·6H₂O** lose water to form anhydrous salts.
- **Ca(NO₃)₂** decomposes to CaO, NO₂, and O₂.
- **NaNO₂** decomposes to NaNO₃ and gaseous products.

Each compound behaves differently upon heating due to their distinct chemical properties and structures.