LAVOISIER’S OXYGEN THEORY OF BURNING A CASE STUDY Up to the 18th Century, people believe that the substances which readily burned contained a sort of spirit called “ Phlogiston”, which escaped into the air during burning. This belief then called the phlogiston theory of burning, lasted for many years. Joseph Priestley, an English clergyman and amateur scientist believed in it. In 1774 Priestley, using a lens, focused the sun’s rays on mercuric oxide, a strange gas was formed. He continued experimenting with mercuric oxide, and collected the gas that was evolved from it when heated strongly. He observed that the candle burned brightly in the presence of unknown gas. And felt wonderful light when he inhaled some of the gas. Thus, he described it as perfect air or very active air. Sometimes later, Priestley, visited a friend, Antoine Lavoisier, a brilliant French chemist told Lavoisier his discovery. Lavoisier pondered over Priestley’s discovery for months. He wondered why the red gave off gas when heated… how it got gas in the first place. He asked himself: what really happens when a substance burns-does it give off something (phlogiston theory of burning), or does it combine with something from the air? If something is given off, then it would mean a decrease with mass after burning. If something from the air combines with a substance during burning, then it would mean an increase in the mass after burning. He suspected that the latter was probably the case. He tested his hypothesis. He reproduced Priestley’s experiment under more carefully controlled conditions (quantitative observations rather than qualitative observations only). Lavoisier put mercury into a glass vessel, and sealed it. He weighed the vessel and its contents, then applied heat to it. A red powder soon appeared inside the vessel. He weighed the vessel again, then compared it before heating. There was no change in mass. This is expected since the vessel was sealed. Nothing has entered or escaped from it during heating. When Lavoisier broke the glass seal, air rushed into the vessel. This phenomenon indicated that some of the air rushed into the vessel must have been used up during the heating process and left space for more air to enter. Lavoisier assumed that part of the air in the vessel must have combined with mercury to form the red powder. Lavoisier, however did not jumped into any hasty conclusion. He wanted more proofs. He continued the investigation but, this time, he reversed the experiment. He put mercuric oxide in a vessel and heated it to a high temperature. He found that a) the red powder was changed back into mercury, and b) a gas was released in the process. This was exactly the same gas which priestly observed. Lavoisier finally concluded that this gas which he called oxygen, combines with combustible materials when they burn. This is called oxygen theory of burning, which is now the accepted explanation for burning. QUESTIONS: ANSWERS MUST BE VERY SPECIFIC AND BASED ON THIS CASE STUDY ONLY. 1.A. in paragraph no.3 Priestly shared with Lavoisier his discovery of a “perfect air”. Which of the scientific traits did Priestly exhibit in this paragraph ? Choose one trait only. How is the trait used in science? A. patience B. gratitude C. open-mindedness D. acceptance of failure 2. State the problem that Lavoisier decided to investigate. 3. -4. State the Hypothesis (to answer the problem in no.2 above) by completing the following sentences. 3. If__________________________________________________________________________________ 4. then_______________________________________________________________________________ 5. Which paragraph described the experiment that Lavoisier performed to test his hypothesis? Give only the number of the paragraph. 6. In paragraph number 6 why did air rush into the vessel when Lavoisier broke the glass seal? 7. Which paragraph shows Lavoisier’s INTERPRETATION of his OBSERVATIONS. Give only the number of the paragraph. 8. What conclusion did Lavoisier draw from his investigation? 9.A. What trait did Lavoisier show in paragraph no.7? Choose one trait only. Why is the trait useful in scientific investigations? A. humility B. open-mindedness C. acceptance of failure D. perseverance 10. Differentiate qualitative observations from quantitative observations. Who between Lavoisier and Priestley made use of qualitative observations observations?
Ideal and Real Gases
Ideal gases obey conditions of the general gas laws under all states of pressure and temperature. Ideal gases are also named perfect gases. The attributes of ideal gases are as follows,
Gas Laws
Gas laws describe the ways in which volume, temperature, pressure, and other conditions correlate when matter is in a gaseous state. The very first observations about the physical properties of gases was made by Robert Boyle in 1662. Later discoveries were made by Charles, Gay-Lussac, Avogadro, and others. Eventually, these observations were combined to produce the ideal gas law.
Gaseous State
It is well known that matter exists in different forms in our surroundings. There are five known states of matter, such as solids, gases, liquids, plasma and Bose-Einstein condensate. The last two are known newly in the recent days. Thus, the detailed forms of matter studied are solids, gases and liquids. The best example of a substance that is present in different states is water. It is solid ice, gaseous vapor or steam and liquid water depending on the temperature and pressure conditions. This is due to the difference in the intermolecular forces and distances. The occurrence of three different phases is due to the difference in the two major forces, the force which tends to tightly hold molecules i.e., forces of attraction and the disruptive forces obtained from the thermal energy of molecules.
LAVOISIER’S OXYGEN THEORY OF BURNING
A CASE STUDY
- Up to the 18th Century, people believe that the substances which readily burned contained a sort of spirit called “ Phlogiston”, which escaped into the air during burning. This belief then called the phlogiston theory of burning, lasted for many years. Joseph Priestley, an English clergyman and amateur scientist believed in it.
- In 1774 Priestley, using a lens, focused the sun’s rays on mercuric oxide, a strange gas was formed. He continued experimenting with mercuric oxide, and collected the gas that was evolved from it when heated strongly. He observed that the candle burned brightly in the presence of unknown gas. And felt wonderful light when he inhaled some of the gas. Thus, he described it as perfect air or very active air.
- Sometimes later, Priestley, visited a friend, Antoine Lavoisier, a brilliant French chemist told Lavoisier his discovery.
- Lavoisier pondered over Priestley’s discovery for months. He wondered why the red gave off gas when heated… how it got gas in the first place. He asked himself: what really happens when a substance burns-does it give off something (phlogiston theory of burning), or does it combine with something from the air? If something is given off, then it would mean a decrease with mass after burning. If something from the air combines with a substance during burning, then it would mean an increase in the mass after burning. He suspected that the latter was probably the case. He tested his hypothesis. He reproduced Priestley’s experiment under more carefully controlled conditions (quantitative observations rather than qualitative observations only).
- Lavoisier put mercury into a glass vessel, and sealed it. He weighed the vessel and its contents, then applied heat to it. A red powder soon appeared inside the vessel. He weighed the vessel again, then compared it before heating. There was no change in mass. This is expected since the vessel was sealed. Nothing has entered or escaped from it during heating.
- When Lavoisier broke the glass seal, air rushed into the vessel. This phenomenon indicated that some of the air rushed into the vessel must have been used up during the heating process and left space for more air to enter. Lavoisier assumed that part of the air in the vessel must have combined with mercury to form the red powder.
- Lavoisier, however did not jumped into any hasty conclusion. He wanted more proofs. He continued the investigation but, this time, he reversed the experiment. He put mercuric oxide in a vessel and heated it to a high temperature. He found that a) the red powder was changed back into mercury, and b) a gas was released in the process. This was exactly the same gas which priestly observed. Lavoisier finally concluded that this gas which he called oxygen, combines with combustible materials when they burn. This is called oxygen theory of burning, which is now the accepted explanation for burning.
QUESTIONS: ANSWERS MUST BE VERY SPECIFIC AND BASED ON THIS CASE STUDY ONLY.
1.A. in paragraph no.3 Priestly shared with Lavoisier his discovery of a “perfect air”. Which of the scientific traits did Priestly exhibit in this paragraph ? Choose one trait only. How is the trait used in science?
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A. patience
B. gratitude
C. open-mindedness
D. acceptance of failure
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2. State the problem that Lavoisier decided to investigate.
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3. -4. State the Hypothesis (to answer the problem in no.2 above) by completing the following sentences.
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3. If__________________________________________________________________________________ 4. then_______________________________________________________________________________
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5. Which paragraph described the experiment that Lavoisier performed to test his hypothesis? Give only the number of the paragraph.
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6. In paragraph number 6 why did air rush into the vessel when Lavoisier broke the glass seal?
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7. Which paragraph shows Lavoisier’s INTERPRETATION of his OBSERVATIONS. Give only the number of the paragraph.
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8. What conclusion did Lavoisier draw from his investigation?
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9.A. What trait did Lavoisier show in paragraph no.7? Choose one trait only. Why is the trait useful in scientific investigations?
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A. humility
B. open-mindedness
C. acceptance of failure
D. perseverance
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10. Differentiate qualitative observations from quantitative observations. Who between Lavoisier and Priestley made use of qualitative observations observations?
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