Level: introductory
Reference: Antoine Lavoisier, "Memoir on the calcination of tin in closed vessels and on the cause of the gain in weight which this metal acquires in the operation," Mémoires de l'Académie Royale des Sciences for 1774, 351-67 (published in 1777).
Notes: Antoine Laurent Lavoisier (1743-1794) is considered by many to be the founder of modern chemistry. "Founder" is a formidable word, and one which tends to diminish the important work of a founder's contemporaries. Yet Lavoisier was surely a central figure in several watershed events of late 18th-century chemistry. The explanation of combustion, calcination, and respiration in terms of oxygen is surely the best known of Lavoisier's important contributions to chemistry. Lavoisier also was a key figure in a group of French scientists who revised the language of chemistry, introducing a systematic nomenclature whose terms were supposed to convey information about the substances to which they were applied.
Lavoisier was one of the first scientists to apply quantitative methods to chemistry, particularly that of the balance. "Balance" was relevant to Lavoisier's work in more than one sense: a precise balance was his main instrument and the "balance sheet" was an important conceptual tool for him. Lavoisier was a scientific accountant in many of his experiments, making sure to count all of the relevant masses before and after a chemical "transaction." This exercise employs data from one of Lavoisier's early experiments on calcination.
The way this exercise uses Lavoisier's data is anachronistic: every part of it uses concepts Lavoisier did not have available to him. Even the unit to which students are to convert Lavoisier's masses (the gram) would not be introduced for another 20 years, during the French Revolution. (Lavoisier would be part of the committee on weights and measures that developed the metric system, by the way; however, neither that nor other services to the state would keep Lavoisier from the revolutionary guillotine.)
The discovery of oxygen had not yet come to Lavoisier's attention, but experiments such as this would help Lavoisier understand the significance of oxygen. Even without knowing about oxygen, Lavoisier concluded that some portion of the air combined with the tin to make the product of the reaction, that only a certain amount of tin could be transformed by a given quantity of air, and that no material from the fire or external to the sealed vessel participated in the reaction. (This last point was important since the phlogiston theory then prominent held that a metal lost some phlogiston or "matter of fire" in the process of calcination.)
Lavoisier noted that only about 1/5 of the air participated in the reaction. Although he did not belabor the point, he thought of the portion of the air that participated in the reaction as a distinct component of the air. That 1/5 of the atmosphere is, of course, oxygen. In computing the quantity of limiting reagent in part b, this factor of 1/5 reflecting the atmospheric abundance of oxygen is necessary. Using anything more precise than 1/5 would be unsound, mainly because of the variable and unspecified moisture content of the atmosphere. A student who took all of the initial gas to be oxygen would, of course, come up with 0.025 mol as the quantity of limiting reagent.
Solutions: To download solutions, go to:
http://web.lemoyne.edu/giunta/classicalcs/lavoisier.doc
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