A recent Journal of Geoscience Education article by Kovacs (2008) nicely highlighted a number of inquirybased and active-learning techniques that can be used in entry-level meteorology courses. These techniques, including think-pair-share, group activities, role-playing, and jigsaw puzzle activities, were discussed in the context of helping education majors obtain both the scientific content and methods needed to better prepare them for teaching careers. Also mentioned in the article was a common in-class experiment wherein a burning candle sitting in a pool of water is entrapped within a glass jar (the “tumbler” in the title). In this experiment, bubbles may be observed as air escapes out of the jar immediately after it contacts the water. Subsequently, the flame fades suffocates, and the water level inside the jar rises to fill approximately 20% of the total volume of the jar. This candle-and-tumbler experiment can encourage scientific reasoning about complex systems by providing an excellent opportunity for students to make numerous observations, and to conceptualize, discuss, and test multiple hypotheses. Unfortunately, the coincidence that the volume of air replaced by water in the jar is close to the fraction of O2(g) in the atmosphere has led some to misinterpret this experiment as appropriate for measuring the relative amount of oxygen in the atmosphere (e.g., Businger, 1996; Caplan et al., 1994; Kovacs, 2008). At most, only 6% of atmospheric oxygen will be consumed by a fire (Belcher and McElwain, 2008), and when this experiment is conducted using an Erlenmeyer flask or similarly shaped jar, such as a salad dressing jar, the water can rise to fill more than 25% of the jar’s total volume. Other readily accessible classroom experiments, such as one that uses damp steel wool (Birk et al., 1981), are more useful for measuring O2(g) in the atmosphere. The misconception that this experiment measures the proportion of oxygen in the atmosphere has been addressed by a number of researchers (Birk and Lawson, 1999; Glanz, 1963; Peckham, 1993). Yet, the candle-andtumbler experiment continues to be published as an appropriate exercise for determining the fraction of oxygen in the atmosphere. The pervasiveness of this misconception suggests that the explanation for why the water level rises into the jar needs to be revisited. Using C25H52 (pentacosane) to represent the chemical composition of the candle, the chemical reaction that occurs when a candle burns can be expressed as:
Read full abstract
Oct 1, 2012
H F Dacre + 3
Open Access
