Advanced Chemistry Theory - Questions and Answers
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According to Bowler’s Making Modern Science, A Historical Survey, the theory of phlogiston was first stated by Johann Joachim Becher in 1667. In 1703, Georg Ernst Stahl, a professor of medicine and chemistry at Halle, proposed a variant of the theory in which he renamed Becher’s terra pinguis to phlogiston theory and it was in this form that the theory had it influence.
Phlogiston was a fire-like substance without color, odor, taste or mass that every combustible substance was in part composed of, and it was released during combustion (Bowler 56). A substance rich in phlogiston was said to be phlogisticated and once they were burned, they became dephlogisticated and back to their true form, the calx (residual substance in form of fine powder). In general, substances that burned in air were said to be phlogisticated. After trying various experiments of combustion of substances in enclosed space, it became clear that combustion ceased once in an enclosed space. This was evidence enough that air was only capable of absorbing a certain amount of phlogiston, and once air became entirely phlogisticated, it would no longer support combustion, nor could it support life of any kind since its purpose in the respiration process was to remove phlogiston from the body; thus, a calx would never be formed. In conclusion, according to the phlogiston theory, phlogiston’s role in combustion is opposite to the role of oxygen in combustion.
The phlogiston theory and the use of phlogiston in the vocabulary of many chemists remained dominant until French chemist Antoinne-Laurent Lavoisier disproved it with his caloric theory of combustion (Bowler 56). In his theory, Lavoisier showed that combustion requires a gaseous substance that has weight and that its weight can be measured. In his experiments with phosphorous and sulfur, both of which burned readily in air, Lavoisier showed that they both gained weight by combining with air. Using lead calx, Lavoisier was also able to capture a large amount of air that according to phlogiston theory was liberated when the calx was heated. These results hadn’t been explained by phlogiston theory. Even though Lavoisier had come to a realization that combustion involved air, he was still puzzled by the exact composition of air, which was not understood then. It was until 1774 when Lavoisier met with the English natural philosopher and phlogistonist Joseph Priestly, who had experimented with a mercury calx and collected a gas, which supported the burning of a candle and the respiration process of a rat (Bowler 63-66).
During that time, respiration was thought to involve the exhalation of phlogiston, which saturated the air.
While back in Paris, Lavoisier repeated Priestley’s experiments with mercury and other metal calces, and eventually concluded that air was not a simple substance (Bowler 57). He argued that air was composed of two components, that is: one that combined with the metal and supported both respiration and combustion, the other, an asphyxiant and supported neither of the processes. He concluded that combustion was between a metal or organic substance with the component of air that supports combustion and respiration, which he called eminently respirable. He later renamed the flammable component of air oxygen after he found that most acid contained the eminently respirable air (Bowler 70). It was after these experiments, in 1783, that Lavoisier began his full-scale attack on phlogiston, claiming that it was imaginary, according to biographer Douglas McKie. In addition, by 1803, most natural philosophers had argued that the theory of phlogiston was of no irrelevance as it made no contribution to the weight of the substance in any kind of way (Bowler 68).
3. What is the corpuscularism and how did Dalton’s atomic theory differ from corpuscularism?
According to Rene Descartes’ (1596 - 1650 AD) mechanical philosophy of corpuscularism, corpuscularism is an ideology that discusses reality and change in terms of particles and their motion. Descartes described everything in the universe as being made of tiny corpuscles of matter, and that, sensations such as taste or temperature were caused by the various shapes and sizes of tiny pieces of matter (Bowler 35). That is, instead of defining physical reality and analyzing change in terms of the Aristotlelian substance or form with the four classical Aristotle elements of earth, air, fire and water, Descartes believed everything (living or non-living) was composed of tiny particles of matter that were constantly moving to prevent a vacuum (Bowler 36). Descartes’ theory had so much in common with atomism that it is considered to be a different version of it.
The idea that all matter is made up of tiny, indivisible particles, called atoms is believed to have originated in the fifth century B.C. (Bowler 73). But after a considerable number of centuries, not much work had been done in the atomic part of science, and Dalton’s atomic theory (1803 – 1808) was considered different because it had the weight of careful chemical measurements behind it. Dalton’s atomic theory wasn’t just a theory; it was a theory of the structure and behavior of atoms (Bowler 74). Dalton’s atomic theory has three parts that remain relatively unchanged to date. First, it stated that elements consisted of tiny particles called atoms; therefore, they cannot be created, destroyed or divided into smaller particles. Second, an element is considered pure because all atoms of an element were identical. Third, atoms of the same element have the same mass; therefore, elements differed from one another because their atoms are different, particularly by mass. According to the atomic theory, atoms of different elements can combine in a chemical reaction to form chemical compounds in fixed ratios. That is, no matter how much of two or more elements are used in a reaction, the ratios of the final chemical compound would remain fixed.
One of the main differences between Dalton’s atomic theory and corpuscularism was that Dalton’s theory changed the focus of chemical atomism from the atomic parameters of shape and interparticle forces, which were the focus in corpuscularism, to the consideration of relative atomic weights (Dalton’s atomic theory) (Bowler 80). In addition, Dalton’s atomic theory emphasized on characterizing the chemical composition of individual elements or species rather than on the classification and generalization of chemical reactions as was the focus of corpuscularism (Bowler 81). That is, by the end of the eighteenth century, it was possible to characterize the chemical composition of various species at the molar level in terms of composition by weight.
Another key difference between Descartes’ corpuscularism and Dalton’s atomic theory that meant a lot to most Aristotlerian followers was Descartes’ concept of mind/soul duality, which allowed for an independent realm of existence for thought, soul, and most importantly, God (Bowler 64).
4. Dalton in his atomic theory employed two concepts developed by Lavoisier. Discuss those concepts and the way Lavoisier used them.
By the late 1700s also best known as the industrial revolution, the useful practices of engineering and technology had begun to influence many philosophical innovations regarding the composition of matter. Those who speculated on the ultimate nature of matter began to prove their thoughtful experiments with repeatable demonstrations as often as they could.
The development of the atomic theory owes much of its work to Lavoisier and Dalton. Even though much of the ground work was done by Lavoisier, the attribution of the atomic theory was to Dalton. Much of Lavoisier’s work as a chemist mainly dealt with the study of combustion (Bowler 56-57). He was later convinced that when a substance in air, it combined with one of the two components of air that supported respiration and combustion. Later on, he realized that the component of air that supported combustion and respiration was the dephlogisticated air that had been discovered by Joseph Priestley (1733-1804) a few years earlier (Bowler 58). He went on to name it eminently respirable. He later renamed the flammable component of air oxygen after he found that most acid contained the eminently respirable air. After meeting Priestley in 1774, Lavoisier carefully repeated Priestley’s experiments and showed that when mercury is heated in oxygen at a moderate temperature, a red substance, calx of mercury, is formed. But at higher temperatures, the calx decomposes into mercury and oxygen. Lavoisier’s experiments also revealed that the combined masses of mercury and oxygen were equal to the mass of the calx of mercury (Bowler 63-67). This implies that, there was no change in mass upon the formation or decomposition of the calx of mercury. After this observation and a couple of more experiments for proof, Lavoisier hypothesized that this should be true for all chemical changes, and this principle was called the law of conservation of mass.
While working with oxygen, Lavoisier noticed that although oxygen combined with many other substances, it never behaved as a combination of other substances (Bowler 68). That is, Lavoisier could not find a way to break down oxygen into a simpler form of two or more substances. Because of this observation, Lavoisier suggested that oxygen must be an element. This was based on the ideas by ancient Greek philosophers of the fifth century B.C. who speculated that all matter consisted of combinations of earth, air, fire and water (the four elements).
Lavoisier went on to produce the first table of elements, which contained a large number of elements that he included in hope that further research could succeed in decomposing them (Bowler 70). The second element on his list was fire, which he termed as caloric, and the third was light. Both caloric and light are now regarded as forms of energy rather than matter. He believed that the earth substances were combinations of metals with oxygen. Even though his table of elements was incomplete, Lavoisier’s work paved a way into the unveiling of the atomic theory.
In 1808, John Dalton gathered the known experimental works of various natural philosophers to summarize the practical evidence on the composition of matter. In the experimental data, he noticed that distilled water everywhere was analyzed to the same elements, hydrogen and oxygen. This was the same case for the other purified substances that decomposed to the same elements in the same ratio by weight. Using Lavoisier’s definition of an element as a substance that could not be decomposed into simpler substances, Dalton concluded that there was a unique atom for each element.
According to Dalton’s third postulate of the atomic theory, he states that atoms are the basic units of chemical changes involved in chemical reactions; thus, atoms can neither be created, destroyed, divided into simpler parts nor can they be converted into atoms of any other kind. That is, this is concurrently similar to Lavoisier’s law of conservation of mass.
Bowler, Peter J., and Iwan Rhys Morus. Making Modern Science a Historical Survey. Chicago, Ill. [u.a.: University of Chicago, 2005. Print.