Classify Physical/Chemical Change: Zn + Dil H2SO4 MCQs Quiz | Class 9
Class: IX | Subject: Science (Code 086) | Unit: Practicals (Unit I) | Topic: Classify Physical/Chemical Change: Zn + Dil H2SO4. This quiz covers the reaction between Zinc granules and dilute Sulphuric acid, observation of gas evolution, and classification of the reaction. Submit your answers to check your score and download the solution PDF.
Educational Content: Reaction of Zinc with Dilute Sulphuric Acid
This experiment demonstrates a classic single displacement reaction which is also characterized as a chemical change. When Zinc granules react with dilute Sulphuric acid, a vigorous reaction occurs, leading to the formation of a salt and the evolution of hydrogen gas.
1. The Chemical Reaction
The reaction can be represented by the following word and chemical equation:
Zinc + Sulphuric Acid gives Zinc Sulphate + Hydrogen
Zn(s) + H2SO4(aq) gives ZnSO4(aq) + H2(g)
In this reaction, Zinc is more reactive than Hydrogen and displaces it from the acid.
2. Key Observations
- Gas Evolution: Bubbles of a colorless and odorless gas are seen rising from the surface of the zinc granules.
- Pop Sound Test: When a burning matchstick or splinter is brought near the mouth of the test tube, the gas burns with a characteristic ‘pop’ sound. This confirms the gas is Hydrogen.
- Temperature Change: If you touch the bottom of the test tube, it feels hot. This indicates that heat is released, making it an exothermic reaction.
- Residue: The zinc granules gradually disappear (if acid is in excess), and a clear, colorless solution of Zinc Sulphate remains.
3. Classification of the Change
This process is classified as a Chemical Change because:
| Feature | Reasoning |
|---|---|
| New Substance | Zinc Sulphate and Hydrogen gas are new substances formed with different properties from the reactants. |
| Irreversibility | The products cannot be turned back into Zinc and Acid by simple physical means. |
| Energy Change | Heat energy is evolved (Exothermic), which is typical of many chemical reactions. |
Quick Revision Points
- Reactants: Zinc granules (Grey solid) and Dilute H2SO4 (Colorless liquid).
- Products: Zinc Sulphate (Colorless solution) and Hydrogen gas.
- Type: Displacement Reaction / Exothermic Reaction / Chemical Change.
- Precaution: Use dilute acid carefully; hydrogen gas is highly flammable.
Extra Practice Questions
- Why are zinc granules preferred over a zinc block? (Answer: Granules have a larger surface area, making the reaction faster.)
- What would happen if we used dilute Hydrochloric acid (HCl) instead of H2SO4? (Answer: Similar reaction; Zn + 2HCl gives ZnCl2 + H2.)
- Is the resulting solution colored? (Answer: No, ZnSO4 solution is colorless.)
- Why should we not bring a flame directly to the test tube mouth immediately? (Answer: To avoid a large explosion if a lot of H2 has accumulated; test carefully.)
- Does copper react with dilute H2SO4? (Answer: No, Copper is less reactive than Hydrogen.)
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