CLAR 102 Inquiry in the Natural World - Spring 2005

Student Topic Guide #6 — “Airs” and The Chemical Revolution

Topic Objectives

 1. Understand how the work of Torricelli, Pascal, and Boyle/Hooke led to replacement of Aristotelian concepts of air and vacuum by the ideas that air has weight and elasticity, and that a vacuum is possible.

2. Know how “fixed air,” “inflammable air,” and “dephlogisticated air” were discovered and characterized, and understand how these discoveries undermined the Aristotelian idea that air is an element.

3. Know how the idea of an element evolved from Aristotle to Lavoisier.

4. Understand how the phlogiston hypothesis and Lavoisier’s oxygen hypothesis each explained the phenomena of combustion, calcination of metals, and animal respiration.

5. Understand how quantitative studies of calcination of metals, and of the formation of water from gases, lent support to Lavoisier’s oxygen hypothesis.

Day 1 Monday, 7 March: Meet in Murphy; Reading Assignment text Chapter 12, pp. 139 - 149

Questions for Discussion

1. What observations led to the construction of the first barometer? How would Aristotle have explained these observations?

2. What evidence did Torricelli and Pascal have that we live “under a sea of air” that weighs down on us?

3. How did Boyle and Hooke’s experiments with an air pump provide further evidence for this hypothesis, and also for the “spring” of air?

Day 2 Wednesday, 9 March: Reading Assignment text Chapter 12, pp. 149 - end

Questions for Discussion

1) State the law of “conservation of mass.” Describe how Black used this concept to explain his observations concerning magnesia alba, magnesia usta, and his “fixed air.”

2) What observations caused Black, Cavendish, and Priestley to conclude that Black’s “fixed air” was different from common atmospheric air?

3) What are the special characteristics of other “airs” besides Black’s “fixed air”?

Day 3 Friday, 11 March: Reading Assignment text Chapter 13, pp. 156 - 160

Questions for Discussion

1) How was Lavoisier’s idea of an element similar to earlier ideas of elements, and how was it different?

2) Explain the following phenomena according to (a) the phlogiston hypothesis; and (b) Lavoisier’s oxygen hypothesis:

i) charcoal burns, producing fire and heat and leaving ash behind

ii) metals change into earthy materials called “calxes” when heated in contact with air

iii) metals can be obtained by heating their calxes (ores) in contact with charcoal or coke

iv) when covered by an air-tight container, a candle goes out, and an animal dies

Day 4 Monday, 14 March: Reading Assignment text Chapter 13, pp. 160 - end

Questions for Discussion

1) What specific observations helped Lavoisier’s oxygen hypothesis prevail over the phlogiston hypothesis?

2) For what other reasons did the majority of chemists in the late 1700s prefer Lavoisier’s oxygen hypothesis over the phlogiston hypothesis?

3) Summarize the major changes that made up the Chemical Revolution.