Law of multiple proportions
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In chemistry, the law of multiple proportions is one of the basic laws of stoichiometry, alongside the law of definite proportions. It is sometimes called Dalton's Law after its discoverer, the English chemist John Dalton,[1] [2] who published it in 1804.[3]
The statement of the law is:
If two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers.[4]
For example carbon oxide: CO and CO2, 100 grams of carbon may react with 133 grams of oxygen to produce carbon monoxide, or with 266 grams of oxygen to produce carbon dioxide. The ratio of the masses of oxygen that can react with 100 grams of carbon is 266:133 ≈ 2:1, a ratio of small whole numbers. The Law of Multiple Proportions, is just what the name suggests, the law of multiple proportions of one constant element within differing compounds sharing the same type of chemical bonding.
John Dalton first expressed this observation in 1804.[5] A few years previously, the French chemist Joseph Proust had proposed the law of definite proportions, which expressed that the elements combined to form compounds in certain well-defined proportions, rather than mixing in just any proportion; and Antoine Lavoisier proved the law of conservation of mass, which helped out Dalton.[6] Careful study of the actual numerical values of these proportions led Dalton to propose his law of multiple proportions.[7] This was an important step toward the atomic theory that he would propose later that year, and it laid the basis for chemical formulas for compounds.
The law of multiple proportions is best demonstrated using simple compounds. For example, if one tried to demonstrate it using the hydrocarbons decane (chemical formula C10H22) and undecane (C11H24), one would find that 100 grams of carbon could react with 18.46 grams of hydrogen to produce decane or with 18.31 grams of hydrogen to produce undecane, for a ratio of hydrogen masses of 121:120, which is hardly a ratio of "small" whole numbers.
[edit] References
- ^ Helmenstine, Anne. "Law of Multiple Proportions Problem". 1. http://chemistry.about.com/od/workedchemistryproblems/a/law-of-multiple-proportions-problem.htm. Retrieved 31 January 2012.
- ^ http://groups.molbiosci.northwestern.edu/holmgren/Glossary/Definitions/Def-L/law_multiple_proportions.html
- ^ http://www.britannica.com/EBchecked/topic/397165/law-of-multiple-proportions
- ^ http://groups.molbiosci.northwestern.edu/holmgren/Glossary/Definitions/Def-L/law_multiple_proportions.html
- ^ http://www.britannica.com/EBchecked/topic/397165/law-of-multiple-proportions
- ^ http://www.chemtopics.com/aplab/lawmp.pdf
- ^ http://www.chemtopics.com/aplab/lawmp.pdf
