Classify Physical/Chemical Change: Heat CuSO4 Crystals MCQs Quiz | Class 9
Class: IX | Subject: Science (Code 086) | Unit: Practicals (Unit I) | Topic: Heating copper sulphate crystals, color change, water loss, and classification. Submit answers to check your score and download the PDF solution.
Overview: Heating Copper Sulphate Crystals
In the Class 9 Science practicals (Unit I), students perform an experiment to classify the heating of copper sulphate crystals as a physical or chemical change. The primary focus is observing the change in color and the evolution of water droplets, which signifies the loss of water of crystallization.
Key Observations
1. Initial State: Copper sulphate crystals (Hydrated Copper Sulphate) are blue in color. The chemical formula is CuSO4.5H2O.
2. Heating Process: When heated in a dry boiling tube:
- The crystals lose their water of crystallization.
- The blue color fades and eventually turns into a white powder (Anhydrous Copper Sulphate).
- Water droplets appear on the cooler upper parts of the boiling tube.
3. Reversibility: When a few drops of water are added to the white anhydrous powder, the blue color is restored, and heat is evolved (exothermic).
Is it a Physical or Chemical Change?
| Aspect | Description |
|---|---|
| Composition | Changes from Hydrated (CuSO4.5H2O) to Anhydrous (CuSO4). Chemical bonds holding water molecules are broken. |
| Classification | Chemical Change (Decomposition/Dehydration). Although reversible, the change in chemical composition defines it as chemical in the context of this practical. |
Quick Revision Points
- Hydrated Copper Sulphate: Blue, contains 5 molecules of water of crystallization.
- Anhydrous Copper Sulphate: White, no water molecules.
- Action of Heat: CuSO4.5H2O (Blue) + Heat -> CuSO4 (White) + 5H2O.
- Safety: Always keep the mouth of the test tube pointed away from yourself and neighbors while heating.
Extra Practice Questions
- Why do water droplets form on the test tube walls? (Ans: Due to condensation of water vapor released from crystals.)
- Is the reaction exothermic or endothermic when adding water back? (Ans: Exothermic – heat is released.)
- What happens if you heat the white powder very strongly? (Ans: It may decompose further into copper oxide and sulphur oxides, turning black.)
- Does the mass of the substance increase or decrease after heating? (Ans: Decrease, due to loss of water mass.)
- What is the common name for hydrated copper sulphate? (Ans: Blue Vitriol.)
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