Laws of Chemical Combination (Overview) MCQs Quiz | Class 9
This Class IX Science (Code 086) quiz covers Unit I: Matter – Its Nature and Behaviour, specifically focusing on the Laws of Chemical Combination. Test your conceptual understanding and ability to recognize law-based statements regarding the Law of Conservation of Mass and Law of Constant Proportions. Answer the 10 questions below, submit to see your score, and download the full solution PDF for your exam preparation.
Overview of Laws of Chemical Combination
In Class 9 Science, Unit I, the study of matter leads to the foundational principles governing chemical reactions. These principles, known as the Laws of Chemical Combination, were established after much experimentation by Antoine L. Lavoisier and Joseph L. Proust. They form the basis for Dalton’s Atomic Theory.
1. Law of Conservation of Mass
Proposed by Antoine L. Lavoisier in 1774. This law states that mass can neither be created nor destroyed in a chemical reaction. Consequently, the total mass of the reactants must equal the total mass of the products.
- Example: If 100g of Calcium Carbonate is heated to produce 56g of Calcium Oxide, the remaining mass (44g) is Carbon Dioxide. Total Mass (100g) = 56g + 44g.
2. Law of Constant Proportions
Proposed by Joseph L. Proust in 1799. This law states that in a chemical substance, the elements are always present in definite proportions by mass. This is also known as the Law of Definite Proportions.
- Example: In pure water, the ratio of the mass of hydrogen to the mass of oxygen is always 1:8, regardless of the source of the water (river, rain, or tap).
- Example: In ammonia, nitrogen and hydrogen are always present in the ratio 14:3 by mass.
Comparison Table
| Law | Scientist | Key Concept |
|---|---|---|
| Conservation of Mass | Antoine Lavoisier | Mass Reactants = Mass Products |
| Constant Proportions | Joseph Proust | Fixed mass ratio of elements |
Extra Practice Questions
- What is the ratio of Hydrogen to Oxygen by mass in water? (Ans: 1:8)
- If 3g of carbon burns in 8g of oxygen to form 11g of CO2, how much CO2 forms if 3g carbon is burnt in 50g oxygen? (Ans: 11g, governed by Constant Proportions)
- Which postulate of Dalton’s theory explains the Law of Constant Proportions? (Ans: The relative number and kinds of atoms are constant in a given compound)
- Does the source of a compound affect its chemical composition? (Ans: No)
- Who is known as the father of modern chemistry for his work on combustion and mass conservation? (Ans: Lavoisier)
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