3/19/2015
Law of multiple proportions - Chemwiki
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ChemWiki: The Dynamic Chemistry E-textbook > Physical Chemistry > Atomic Theory > Postulates of Dalton's atomic theory > Law of multiple
proportions
Law of multiple proportions
John Dalton (1803) stated, "'When two elements combine with each other to form two or more compounds, the ratios of the masses of one element
that combines with the fixed mass of the other are simple whole numbers'.
Example
Carbon monoxide (
): 12 parts by mass of carbon combines with 16 parts by mass of oxygen.
Carbon dioxide (
): 12 parts by mass of carbon combines with 32 parts by mass of oxygen.
Ratio of the masses of oxygen that combines with a fixed mass of carbon (12 parts): 16:32 or 1:2
Hydrogen and oxygen are known to form 2 compounds. The hydrogen content in one is 5.93%, and that of the other is 11.2%. Show that this data
illustrates the law of multiple proportions.
SOLUTION
In the first compound: hydrogen = 5.93%
Oxygen = (100 -5.93) = 94.07%
In the second compound: hydrogen = 11.2%
Oxygen = (100 -11.2) = 88.88%
Ratio of the masses of oxygen that combine with fixed mass of hydrogen: 15.86:7.9 or 2:1. This is consistent with the law of multiple proportions.
Contributors
Binod Shrestha (University of Lorraine)
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