How can we detect presence of Carbon dioxide in reaction?

Answer

To detect the presence of carbon dioxide in a reaction, we can follow these steps:

### Step-by-Step Solution:

1. **Prepare Lime Water**:
- Lime water is a saturated solution of calcium hydroxide (Ca(OH)₂) in water. Start by preparing this solution.

2. **Introduce Carbon Dioxide**:
- Pass carbon dioxide (CO₂) gas through the lime water. This can be done by bubbling the gas into the solution.

3. **Observe the Reaction**:
- Watch for any changes in the appearance of the lime water.

4. **Formation of Calcium Carbonate**:
- If carbon dioxide is present, it will react with calcium hydroxide to form calcium carbonate (CaCO₃), which is insoluble in water.

5. **Milky Appearance**:
- The formation of calcium carbonate will cause the lime water to turn milky or cloudy due to the precipitation of the calcium carbonate.

6. **Conclusion**:
- The appearance of a milky solution indicates the presence of carbon dioxide in the reaction.

### Summary:
- The key reaction is:
\[ \text{Ca(OH)}_2 (aq) + \text{CO}_2 (g) \rightarrow \text{CaCO}_3 (s) + \text{H}_2\text{O} (l) \]
- The milky appearance of lime water confirms the presence of carbon dioxide.