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Baris 1: ~~{{terjemah\|Inggris}}~~ Dalam [[kimia]], '''hukum perbandingan tetap''' atau '''hukum Proust''' (diambil dari nama [[kimiawan]] [[Perancis]] [[Joseph Proust]]) adalah hukum yang menyatakan bahwa suatu [[senyawa kimia]] terdiri dari [[unsur kimia\|unsur-unsur]] dengan perbandingan [[massa]] yang selalu tepat sama. Dengan kata lain, setiap sampel suatu senyawa memiliki komposisi unsur-unsur yang tetap. Misalnya, air terdiri dari <sup>8</sup>/<sub>9</sub> massa [[oksigen]] dan <sup>1</sup>/<sub>9</sub> massa [[hidrogen]]. Bersama dengan [[hukum perbandingan berganda]] (hukum Dalton), hukum perbandingan tetap adalah hukum dasar [[stoikiometri]]. ~~<!--~~ In [[chemistry]], the '''law of definite proportions''' states that a [[chemical compound]] always contains exactly the same proportion of [[chemical element\|elements]] by mass. An equivalent statement is the '''law of constant composition''', which states that all samples of a given chemical compound have the same elemental composition. For example, [[oxygen]] makes up <sup>8</sup>/<sub>9</sub> of the mass of any sample of pure [[water]], while [[hydrogen]] makes up the remaining <sup>1</sup>/<sub>9</sub> of the mass. Along with the [[law of multiple proportions]], the law of definite proportions forms the basis of [[stoichiometry]].<ref>Zumdahl, S. S. “Chemistry” Heath, 1986: Lexington, MA. ISBN: 0-669--04529-2.</ref> {{kimia-stub}} ~~==History==~~ This observation was first made by the [[France\|French]] chemist [[Joseph Proust]] based on several experiments conducted between [[1797]] and [[1804]].{{Fact\|date=February 2007}} Based on such observations, Proust made statements like this one, in 1806: :"I shall conclude by deducing from these experiments the principle I have established at the commencement of this memoir, viz. that iron like many other metals is subject to the law of nature which presides at every true combination, that is to say, that it unites with two constant proportions of oxygen. In this respect it does not differ from tin, mercury, and lead, and, in a word, almost every known combustible." [[Category:~~Chemical~~Ikatan ~~bonding~~kimia]]▼ The law of definite proportions might seem obvious to the modern chemist, inherent in the very definition of a chemical compound. At the end of the [[18th century]], however, when the concept of a chemical compound had not yet been fully developed, the law was novel. In fact, when first proposed, it was a controversial statement and was opposed by other chemists, most notably Proust's fellow Frenchman [[Claude Louis Berthollet]], who argued that the elements could combine in any proportion.{{Fact\|date=February 2007}} The very existence of this debate underscores that at the time, the distinction between pure [[chemical compound]]s and [[mixture]]s had not yet been fully developed. [[Category:~~Chemical~~Tatanama ~~formulas~~kimia]]▼ [[Category:~~Chemical~~Formula ~~nomenclature~~kimia]]▼ The law of definite proportions contributed to, and was placed on a firm theoretical basis by, the [[atomic theory]] that [[John Dalton]] promoted beginning in [[1803]], which explained matter as consisting of discrete [[atom]]s, that there was one type of atom for each element, and that the compounds were made of combinations of different types of atoms in fixed proportions.{{Fact\|date=February 2007}} ~~==Non-stoichiometric compounds==~~ It may be noted that although very useful in the foundation of modern chemistry, the law of definite proportions is not universally true. There exist [[non-stoichiometric compound]]s whose elemental composition can vary from sample to sample. An example is the [[iron oxide]] [[wüstite]], which can contain between 0.83 and 0.95 iron atoms for every oxygen atom, and thus contain anywhere between 23% and 25% oxygen. In general, Proust's measurements were not accurate enough to detect such variations. In addition, the [[isotopic]] composition of an element can vary depending on its source, hence its weight in a pure stoichiometric compound may vary. This fact is used in [[geochemical dating]] since [[astronomy\|astronomical]], [[atmospheric]], [[oceanic]], [[Earth's crust\|crustal]] and deep [[Earth]] processes may concentrate lighter or heavier isotopes preferentially. With the exception of [[hydrogen]] and its isotopes, the effect is usually small but measurable with modern instrumentation. An additional note: many natural [[polymer]]s vary in composition (for instance [[DNA]], [[protein]]s, [[carbohydrate]]s) even when "pure". Polymers are generally not considered "pure chemical compounds" except when their molecular weight is uniform (monodisperse) and their stoichiometry is constant. In this unusual case, they still may violate the "Law" due to isotopic variations. ~~==References==~~ ~~<references/>~~ ▲[[Category:Chemical bonding]] ▲[[Category:Chemical nomenclature]] ▲[[Category:Chemical formulas]] ~~-->~~ [[be:Закон аб нязменнасці ў складзе]] [[de:Gesetz der konstanten Proportionen]]

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