Activity 1: Phlogiston theory

Conceptual understanding: New evidence can lead to a paradigm shift.

In the late 1700s, J. J. Becher proposed phlogiston theory that stated combustible materials contain phlogiston. A more combustible material contains more phlogiston. When burnt, these materials release phlogiston into the air as shown by the diagram to the right (click for link).

1a. Apply phlogiston theory to each of the following observations. What might you deduce in each case?

• ​A candle stops burning 10 s after being placed in a closed container.
• ​Wood burning more vigorously than coal.
• Burning a 10 g plant leaves only 4 g of ash.

1b​. i. What problems might this quantitative data (left) cause in relation to phlogiston theory?​

ii. If all metals gain mass when burned, how might we change our view of the validity of phlogiston theory?

iii. Would this demo (right) support or oppose phlogiston theory?

1c. i. Lavoisier and others eventually put forward oxygen theory as a better explanation of observations. This theory suggested that burning something meant reacting it with oxygen in the air. This could be considered a paradigm shift. What might this term mean?

ii. The flat earth to round earth theory change is a commonly given example of a paradigm shift. What caused to this shift?

iii. What makes one theory better than another? Is it possible that oxygen theory could be refined or replaced?

iv.​ The type of evidence used to support oxygen theory, and improving scientific technology such as vacuum pumps, led to the discovery of the law of the conservation of mass. What is the difference between a theory and a law?