Sodium chloride definite proportions

Table salt (sodium chloride) is another example that shows the law of definite proportions. Any sample of table salt consists of two elements in the following proportions by mass ... 

Dalton s fonrth postulate clearly is related to the law of conservation of mass. The fifth aims to explain the law of definite proportions. Perhaps Dalton s reasoning went something like this Suppose you reject the atomic theory and believe instead that compounds are subdivisible without limit. What, then, ensnres the constancy of composition of a substance snch as sodium chloride Nothing Bnt if each sodium atom in sodium chloride is matched by one chlorine atom, then the constancy of composition can be nnderstood. So in this argument for the law of definite proportions, it does not matter how small the atoms of sodinm and chlorine are. It is important merely that there be some lower bound to the snbdivisibil-ity of matter, because the moment we pnt in snch a lower bound, arithmetic steps in. Matter becomes countable, and the nnits of connting are simply atoms. Believing in the law of definite proportions as an established experimental fact, Dalton postulated the existence of the atom. 

The chemical Law of Definite Proportions, which expresses the notion that a pure compound always has a fixed and consistent composition in terms of the elements it contains, is an exact law for many, perhaps most compounds. There is nothing approximate in the assertion that pure sodium chloride contains equal numbers of sodium and chlorine atoms and, therefore, 61.72% chlorine, or that pure water contains just twice as many hydrogen atoms as oxygen and, therefore, 11.19% hydrogen. The whole of analytical chemistry is based on the reliability of such ratios. But there are a few classes of material that chemists would prefer to regard as pure compounds that do not show this consistency of composition. The Law of Definite Proportions is an exact law, but one that has clear exceptions. 

Compounds Most substances are compounds. A compound is a substance composed of two or more elements chemically combined. By the end of the eighteenth century, Lavoisier and others had examined many compounds and showed that all of them were composed of the elements in definite proportions by mass. Joseph Louis Proust (1754-1826), by his painstaking work, convinced the majority of chemists of the general validity of the law of definite proportions (also known as the law of constant composition) a pure compound, whatever its source, always contains definite or constant proportions of the elements by mass. For example, 1.0000 gram of sodium chloride always contains 0.3934 gram of sodium and 0.6066 gram of chlorine, chemically combined. Sodium chloride has definite proportions of sodium and chlorine that is, it has constant or definite composition. ... 

Two samples of sodium chloride were decomposed into their constituent elements. One sample produced 6.98 g of sodium and 10.7 g of chlorine, and the other sample produced 11.2 g of sodium and 17.3 g of chlorine. Are these results consistent with the law of definite proportions Explain your answer. 

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