Laws Of Chemical Combination
Easychemistry
Carbon reacts with oxygen to form two different oxides: CO and CO₂. In CO, the ratio of carbon to oxygen by mass is 3:4, and in CO₂ it is 3:8. This observation is best explained by which law?
Select the correct option:
Solution
Incorrect! Answer:
Law of Multiple Proportions
- Identify the Context: Carbon forms two compounds with oxygen — CO and CO₂. The same two elements combine in different mass ratios in different compounds.
- Apply the Law of Multiple Proportions (Dalton, 1803): When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.
- Verify the Ratio: Keeping the mass of carbon fixed at 3 g:
- In CO, oxygen = 4 g.
- In CO₂, oxygen = 8 g.
- Ratio of oxygen masses = 48=12, a simple whole-number ratio.
- Why Not the Others?
- Law of Conservation of Mass deals with total mass in a reaction, not composition ratios.
- Law of Definite Proportions states a single compound always has fixed composition — it does not compare two compounds.
- Avogadro's Law relates gas volumes, not mass ratios.
- Conclusion: The observation directly illustrates the Law of Multiple Proportions.
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About This Question
- Subject
- chemistry
- Chapter
- some basic concepts in chemistry
- Topic
- laws of chemical combination
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Law of Multiple Proportions
- Identify the Context: Carbon forms two compounds with oxygen — CO and CO₂. The same two elements combine in different mass ratios in different compounds.
- Apply the Law of Multiple Proportions (Dalton, 1803): When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.
- Verify the Ratio: Keeping the mass of carbon fixed at 3 g:
- In CO, oxygen = 4 g.
- In CO₂, oxygen = 8 g.
- Ratio of oxygen masses = 48=12, a simple whole-number ratio.
- Why Not the Others?
- Law of Conservation of Mass deals with total mass in a reaction, not composition ratios.
- Law of Definite Proportions states a single compound always has fixed composition — it does not compare two compounds.
- Avogadro's Law relates gas volumes, not mass ratios.
- Conclusion: The observation directly illustrates the Law of Multiple Proportions.
This easy difficulty chemistry question is from the chapter some basic concepts in chemistry, covering the topic of laws of chemical combination. It appeared in the 2025 exam.
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