This is the new updated edition of the first book in the bestselling Uncovering Student Ideas in Science series. Like the first edition of volume 1, this book helps pinpoint what your students know (or think they know) so you can monitor their learning and adjust your teaching accordingly. Loaded with classroom-friendly features you can use immediately, the book includes 25 “probes”—brief, easily administered formative assessments designed to understand your students’ thinking about 60 core science concepts.

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The purpose of this assessment probe is to elicit students’ ideas about conservation of matter during combustion. The probe is designed to find out if students think the mass changes as paper burns inside a closed system.

Familiar Phenomenon

chemical change, closed system, combustion, conservation of matter

The best answer is C: The total mass before and after burning is the same. Burning is an example of combustion—a chemical change in which a substance containing hydrocarbons combines with oxygen to produce carbon dioxide and water. It also releases energy in the form of heat and light. When the carbon and hydrogen of the hydrocarbon-containing substance (i.e., the paper) chemically combine with the oxygen, the remaining materials may appear as ash, the solid remains of a fire. Although the hydrocarbons appear to “vanish” during the reaction with oxygen to form gaseous carbon dioxide and water vapor, the total mass or weight of the reactants (hydrocarboncontaining substance and oxygen in the air) and products (carbon dioxide, water, and ash) remain the same. In a closed system containing air, a piece of paper, and a match, no mass or weight is added or lost as the paper burns.

Gases play a big part in the interaction that occurs inside the jar. Many students have observed wood burning in a fireplace or other structure and they see that many pounds of wood seem to “disappear” with only ash left. What they do not see are the many pounds of gas given off that leave through the chimney. It is important for students to think about the interaction of all materials inside the jar.

Elementary Students

In the elementary grades, students begin developing ideas about changes in objects and materials. They can recognize the formation of soot or ash as a change in the appearance of the paper. Upper-elementary students begin to distinguish between physical and chemical changes on the basis of changes in observable properties. Conservation of matter in the elementary grades focuses on parts and wholes of objects and changes of state. Although the chemical details are too sophisticated to be addressed at this age level, the probe can be used to find out elementary students’ intuitive ideas about the conservation of matter in a closed system.

Middle School Students

In the middle grades, students link ideas about chemical change with formation of new substances. Burning (combustion) is commonly used as an example of a chemical change that results in a new substance with properties that differ from the original substance. These basic ideas about chemical change are included as grade-level expectations in the national standards. However, the mechanism of that change, explained by the interaction among hydrogen, carbon, and oxygen atoms, is a more sophisticated idea developed in high school. The probe is useful in determining students’ initial ideas about what burning and the combustion process are.

By the end of middle school, all students should know that matter or mass is conserved in a closed system as well as in chemical reactions. Conservation ideas about objects begin in elementary grades and increase in cognitive sophistication as the ideas of atoms, interactions, transformations, and closed systems are considered. Transformation of matter is addressed in middle school, although it remains a difficult concept and one in which students may have difficulty applying conservation reasoning. The notion that gases are involved in the interaction may be missing, and the “disappearance” of the paper may influence students’ thinking that the paper is breaking down and losing mass. Knowing the ideas that students hold prior to learning that oxygen combines with substances in the paper during a combustion reaction is useful in designing learning experiences that challenge their intuitive notions influenced by observation.

High School Students

Students at the high school level make a transition from a basic understanding of types of chemical changes, including composition, decomposition, and single and double replacement reactions, to understanding the mechanism for the reaction. Conservation of matter or mass at the high school level is an idea applied to other matter-related ideas in biological, physical, and geological contexts. The probe is useful in determining whether students recognize a closed system as justification for matter or mass being conserved during a chemical change. The probe is also useful in determining whether students still hold on to preconceived ideas about burning, even after they have received middle school instruction targeted toward the idea that in a combustion reaction, oxygen combines with certain materials to form carbon dioxide and water.

Be sure students understand that the air, paper, and match are contained in a sealed jar and nothing can enter or escape from the jar. It may help to have visual props for this probe. Light a match and seal it in a jar containing a crumpled wad of paper. Have students observe the paper as it burns. Ask students to consider what happened to the total weight or mass of the system. Note: You may wish to substitute the word mass with the word weight if using this probe with elementary school students.

The probe “Nails in a Jar” (p. 31), along with several probes in Volume 1 of this series (Keeley, Eberle, and Farrin 2005), can be used to further probe students’ ideas about conservation of matter or chemical changes involving oxygen.

• Studies of 11- and 12-year-olds’ ideas about the role of air in burning suggest that most know that air is needed for burning, but the function of air is not generally understood (Driver et al. 1994).
• Students may realize that oxygen is necessary for combustion but may not understand how it interacts with the material. Some combustibles are said to have “melted” or “evaporated,” or the combustible substance is thought to be made up of the substances that eventually appear as products (Driver et al. 1994).
• More than half of a group of 15-year-olds considered to have “above average ability” predicted loss of mass on the combustion of a sample of iron wool (Driver et al. 1994).
• Many students do not recognize the quantitative aspects of a chemical change and the conservation of overall mass (Driver et al. 1994).
• Middle and high school students’ thinking about chemical change tends to be dominated by the obvious features of the change. Some students think that when something is burned in a closed container, it will weigh more because they see the smoke that was produced (AAAS 1993).
• For chemical reactions that evolve gas, mass conservation is more difficult for students to grasp (AAAS 1993). If a chemical reaction results in the apparent disappearance of some materials, students may not know that mass is conserved (Driver et al. 1994).

American Association for the Advancement of Science (AAAS). 2007. Atlas of science literacy. Vol. 2. (See “The Chemical Revolution” map, pp. 80–81.) Washington, DC: AAAS

Cobb, C., and M. L. Fetterolf. 2005. The joy of chemistry: The amazing science of familiar things. Amherst, NY: Prometheus Books.

Keeley, P. 2005. Science curriculum topic study: Bridging the gap between standards and practice. Thousand Oaks, CA: Corwin Press.

Keeley, P., F. Eberle, and L. Farrin. 2005. Uncovering student ideas in science: 25 formative assessment probes. Arlington, VA: NSTA Press.

National Science Teachers Association (NSTA). 2005. Properties of objects and materials. NSTA SciGuide. Online at http://learningcenter. nsta.org/product_detail.aspy?id=10.2505/5/ SG-01.

Robertson, W. 2007. Chemistry basics: Stop faking it! Finally understanding science so you can teach it. Arlington VA: NSTA Press.

• This probe can be followed up as an inquiry-based demonstration. Ask the question and encourage students to commit to a prediction. Test it by finding the total mass of a jar, lid, paper, and match and then burning the paper in the jar with the match inside and the lid tightly sealed. Have students discuss the evidence and connect the results to the scientific principle of conservation of mass during a chemical reaction: Mass is not created or destroyed in a chemical reaction, but atoms and molecules are rearranged to form new products. However, be sure students are finding the mass within the limits of precision of the scale that is used.
• Reinforce the idea of conservation of mass during a chemical reaction in which a gas is a reactant by exploring additional reactions in closed systems. For example, clean a Ping-Pong-ball-size piece of iron wool (commonly called “steel wool”) by dipping it in vinegar and then drying it. Place it in a flask and stretch a deflated balloon over the top of the flask. Record the mass of this system before and after the wool “rusts” and the balloon gets “sucked in” to the flask. Discuss the observations and connect the results to the scientific principle of conservation of mass during a chemical reaction, placing particular emphasis on the phenomenon of “disappearing gas.”
• Reinforce the idea of conservation of mass during a chemical reaction in which a gas is produced by exploring reactions of everyday substances in closed systems. For example, record the mass of an effervescent tablet in a balloon that is sealed over a flask of water before and after the tablet is dropped into the water. Discuss the observations and connect the results to the scientific principle of conservation of mass during a chemical reaction, placing particular emphasis on the evidence of gas production.
• Help students draw parallels between the types of chemical change that involve combination with oxygen, such as oxidation and combustion reactions.
• With older students, connect this probe to the history of science by sharing how Antoine Lavoisier’s idea of conservation of matter became the centerpiece of the modern science of chemistry. Recount Lavoisier’s careful measurement of substances involved in burning to show that there was no net gain or loss of weight.