Law of Conservation of Mass (Verification) MCQs Quiz | Class 9

Class IX Science (Code 086), Unit: Practicals (Unit III). This quiz covers the verification of the Law of Conservation of Mass involving closed system reactions, comparison of mass before and after chemical changes, and interpretation of results. Submit your answers to view the detailed solution and download the PDF result.

Understanding the Law of Conservation of Mass

The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. This means that in a closed system, the total mass of the reactants must equal the total mass of the products.

Verification Experiment

In the Class 9 practical syllabus, this law is often verified using the reaction between Barium Chloride and Sodium Sulphate.

  • Reactants: Barium Chloride solution (colorless) and Sodium Sulphate solution (colorless).
  • Procedure: A small ignition tube containing one solution is placed inside a conical flask containing the other solution. The flask is sealed with a cork to create a closed system.
  • Reaction: When mixed, a chemical reaction occurs forming a white precipitate.
  • Chemical Equation:
    BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)

Key Observations & Conclusions

Parameter Observation
Before Mixing Two clear, colorless liquids separated in the flask.
After Mixing Formation of a white precipitate (Barium Sulphate).
Mass Check Mass of flask before reaction = Mass of flask after reaction.

Important Precautions

  1. Closed System: The flask must be corked tightly to prevent any matter (like gas or vapors) from escaping, which would alter the mass reading.
  2. Careful Handling: The ignition tube should be hung carefully so the solutions do not mix before the initial weighing.
  3. Accuracy: A sensitive digital balance should be used for accurate measurements.

Quick Revision Points

  • The law was proposed by Antoine Lavoisier in 1774.
  • It applies to both physical and chemical changes.
  • Mass is conserved because atoms are rearranged, not created or destroyed.