All questions of Chemical Changes and Reactions for Class 6 Exam

Understanding Solubility in Water
When considering which substances dissolve in water, it's essential to look at their chemical properties and interactions with water molecules.
Substances in the Options
- Sodium Chloride (NaCl):
- This is table salt and is highly soluble in water. When added, it dissociates into sodium and chloride ions, resulting in a clear solution.
- Calcium Carbonate (CaCO3):
- This compound is primarily found in chalk and limestone. It has low solubility in water, and when added to water, it does not dissolve well. Instead, it forms a cloudy suspension.
- Copper Sulfate (CuSO4):
- Copper sulfate is moderately soluble in water. When dissolved, it produces a blue solution, indicating that it readily mixes with water.
- Potassium Nitrate (KNO3):
- This substance is also highly soluble in water, forming a clear solution when dissolved.
Conclusion: Why Calcium Carbonate is the Correct Answer
- Calcium Carbonate’s Behavior:
- Unlike sodium chloride, copper sulfate, and potassium nitrate, calcium carbonate does not dissolve significantly in water. Its low solubility leads to the formation of a cloudy mixture instead of a clear solution.
- Practical Examples:
- In real-world scenarios, you can observe this property when adding chalk powder (calcium carbonate) to water; it remains suspended, resulting in turbidity.
In summary, calcium carbonate is the substance that does not dissolve in water, thus making the solution appear cloudy.