AllChemicals — The Online Chemical Glossary | https://allchemicals.info/chemical/549-law-of-multiple-proportions
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Quick Reference
Also Known As
Dalton's law of multiple proportions, multiple proportion law
What is Law of Multiple Proportions?
Dalton's law stating that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole-number ratios. For example, CO and CO₂ demonstrate this with carbon-to-oxygen mass ratios of 1:1 and 1:2.
Properties & Characteristics
The Law of Multiple Proportions (Dalton's law, 1803) states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in the ratio of small whole numbers. For example, CO and CO₂: with 12 g of carbon, the oxygen masses are 16 g and 32 g, a ratio of 1:2. This law is explained by the atomic theory — atoms combine in specific whole-number ratios in different compounds.
Uses & Applications
The law of multiple proportions was historical evidence for Dalton's atomic theory and the discreteness of atoms. It explains the existence of different oxides (FeO vs. Fe₂O₃), different chlorides (PCl₃ vs. PCl₅), and different hydrocarbons (CH₄ vs. C₂H₆) with the same elements in different ratios.
Safety Information
No direct safety concern. Different compounds of the same elements (CO vs CO₂, PCl₃ vs PCl₅) can have dramatically different hazards. CO is acutely toxic; CO₂ is an asphyxiant. PCl₃ is more reactive than PCl₅. Always identify the specific compound, not just the elements present.
Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.
SynonymsDalton's law of multiple proportions, multiple proportion law
Frequently Asked Questions
Dalton's law stating that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in simple whole-number ratios. For example, CO and CO₂ demonstrate this with carbon-to-oxygen mass ratios of 1:1 and 1:2.
The law of multiple proportions was historical evidence for Dalton's atomic theory and the discreteness of atoms. It explains the existence of different oxides (FeO vs. Fe₂O₃), different chlorides (PCl₃ vs. PCl₅), and different hydrocarbons (CH₄ vs. C₂H₆) with the same elements in different ratios.
No direct safety concern. Different compounds of the same elements (CO vs CO₂, PCl₃ vs PCl₅) can have dramatically different hazards. CO is acutely toxic; CO₂ is an asphyxiant. PCl₃ is more reactive than PCl₅. Always identify the specific compound, not just the elements present.
Editorial standards: Chemical data is sourced from peer-reviewed literature,
CAS Registry, NIST WebBook, and PubChem. Safety information reflects guidance from OSHA, ECHA,
and IAEA. For educational purposes only — always consult official SDS documentation and qualified
professionals before handling chemicals.
