In chemistry, the law of double proportion is one of the basic laws of stoichiometry used to establish atomic theory, in addition to the laws of conservation of mass (matter) and the law of definite proportions. This is sometimes called Dalton's Law after its discoverer, the English chemist John Dalton, who published it in the first part of the first volume of "The New System of Chemical Philosophy" (1803). Here is a legal statement:
If two elements form more than one compound between them, then the mass ratio of the second element joining the fixed mass of the first element will be the ratio of small integers.
For example, Dalton knows that the carbon element forms two oxides by combining oxygen in different proportions. A fixed carbon mass, say 100 grams, can react with 133 grams of oxygen to produce one oxide, or with 266 grams of oxygen to produce another. The oxygen mass ratio that can react with 100 grams of carbon is 266: 133 = 2: 1, the ratio of small integers. Dalton interprets this result in his atomic theory by proposing (correctly in this case) that two oxides have one and two oxygen atoms each for each carbon atom. In the first modern notation is CO (carbon monoxide) and the second is CO 2 (carbon dioxide).
John Dalton first declared this observation in 1804. A few years earlier, the French chemist Joseph Proust had proposed a definite proportional law , stating that the elements were combined to form a compound in certain, undefined proportions well, rather than mixing only in any proportion; and Antoine Lavoisier proves the law of conservation of the masses, which helped Dalton. The careful study of the true numerical values ​​of this proportion led Dalton to propose his law of some proportion. This is an important step toward the atomic theory he will propose later that year, and it lays the groundwork for the chemical formula for the compound.
Another example of law can be seen by comparing ethane (C 2 H 6 ) with propane (C 3 H 8 ). The weight of hydrogen that joins 1 g of carbon is 0.252 g in ethane and 0.224 g in propane. The weight ratio is 1.125, which can be expressed as a small two-digit ratio of 9: 8.
Video Law of multiple proportions
Limitations
The law of double proportion is best demonstrated by the use of simple compounds. For example, if someone tries to demonstrate it using decane hydrocarbons (chemical formula C 10 H 22 ) and undecane (C 11 H 24 ), one will find that 100 grams of carbon can react with 18.46 grams of hydrogen to produce decane or with 18.31 grams of hydrogen to produce undecane, for a hydrogen mass ratio of 121: 120, which is hardly a small integer ratio ".
The law fails with non-stoichiometric compounds and also does not work well with polymers and oligomers.
Maps Law of multiple proportions
References
Source of the article : Wikipedia
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