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Will It Form a New Substance?

Each of the first four volumes provides 25 probes with easy-to-follow steps for uncovering and addressing students’ ideas by promoting learning through conceptual change instruction. Probes cover topics such as physical, life, and Earth and space science; the nature of science; and unifying themes. Each volume on page 23 provides topic-specific probes. These invaluable books include teacher materials that explain content, identify links to standards, and suggest grade-appropriate ways to present materials so students learn the concepts accurately. Teachers, professional development coordinators, and college science and preservice faculty will find these resources essential and exciting.

 

Will It Form a New Substance?

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Purpose

The purpose of this assessment probe is to elicit students’ ideas about chemical change. The probe is designed to find out how students determine whether a new substance with a different chemical makeup is formed when matter undergoes a change.

Type of Probe

Justified list

Related Concepts

Chemical change, chemical reaction, mixture, physical change, substance

Explanation

The best answers are B, C, F, I, J, K, N, and O. Each of these answer choices is a chemical change because each change results in a new substance that has a different chemical makeup than the original substance or substances. B: When a cake bakes, the baking soda produces bubbles of gas and the proteins from the egg change, binding the ingredients and making the cake firm. C: When a metal bar (iron) rusts, it combines with oxygen in the air and forms iron oxide (a reaction called oxidation). Iron oxide is a different substance from the original metal (iron). F: As an apple is exposed to air it combines chemically with the oxygen in the air, turning the apple brown. This chemical reaction is also an example of oxidation. I: When milk spoils, an acid is produced that gives the milk a sour taste. J: Frying an egg chemically changes the proteins in the egg. K: Burning a piece of wood decomposes the cellulose and releases carbon dioxide, water, and ash (the minerals that were in the wood). N: Other chemical reactions take place as the apple decomposes, releasing new substances such as ethylene gas. O: Several chemical reactions take place in the stomach to break food down into simpler substances that can be used by cells. Acids produced in the stomach along with enzymes react with food in the stomach.

The distracters A, E, and L are changes in which the state of matter (solid, liquid, or gas) changes but is still the same substance chemically. These changes are often referred to as physical changes. D and M are also physical changes. The sugar and salt dissolve in the water but they do not chemically combine with the water to form a new substance. The sugar water and the salt water are mixtures. Both the sugar and salt retain their properties and can be recovered by evaporating the water. In G, the sugar and milk are mixed together and then frozen. The mixture takes on a new form but the milk and sugar do not combine chemically to form a new substance. In H, a gas, helium, fills the balloon and the balloon rises. The helium does not change chemically into a different gas. P is also a physical change. Magnetizing merely changes the alignment of the atoms in the nail. It does not chemically change the iron.

Administering the Probe

This probe is best used with students in grades 3–12. Make sure students know that a new substance means the change results in new matter that has a different chemical makeup and properties that are different from the original matter. For younger students, eliminate answer choices they may not be familiar with.

Related Disciplinary Core Ideas From the Framework (NRC 2012)

3–5 PS1.B: Chemical Reactions

  • When two or more different substances are mixed, a new substance with different properties may be formed.

6–8 PS1.B: Chemical Reactions

  • Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants.

9–12 PS1.B: Chemical Reactions

  • Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangement of atoms into new molecules.

Related Research

  • Although in science the term chemical change refers to processes in which the reacting chemical substances transform into new substances, several studies have found that students often use the term chemical change to encompass a wide variety of changes including physical transformations, especially when the color of a substance changes. How well students make a distinction between chemical and physical changes may depend on their conception of substance. In general, students have difficulty developing the idea of chemical combination of elements until they are able to interpret what combination means at a molecular level (Driver et al. 1994).
  • Students experience difficulty in discriminating consistently between a chemical change and a physical change. Evidence for this comes from a number of studies. For example, Ahtee and Varjola (1998) explored 13–20-year-olds’ ideas about what kind of things would indicate a chemical reaction had occurred. They found that about 20% of the 13–14-year-olds and 17–18-year-olds thought dissolving and change of state were chemical reactions. Only 14% of the 137 19–20-year-old university students in the study could explain what actually happened in a chemical reaction.
  • Vogelezang (1987) found that students who regard ice as a different substance from water are likely to consider freezing water or melting ice as a chemical change.
  • Stavridou and Solomonidou (1989) explored ideas held by Greek students ages 8 to 17 by presenting them with 18 different phenomena to classify as a chemical or physical change. They found that students who used the reversibility criterion were better able to distinguish between chemical and physical changes than students who did not consider reversibility. The students who used the reversibility criterion considered chemical changes to be irreversible, which could pose a problem in understanding chemical reactions. Both groups used criteria that were macroscopic in character.
  • In Abraham, Williamson, and Westbrook’s study (1994), students confused chemical and physical changes. There were indications that they had memorized the terminology rather than developed conceptual understanding.
  • A study by Abraham et al. (1992) presented eighth grade students with a chemical change in which a glass rod is held in the flame of a burning candle and a black film forms on the rod. To show understanding of chemical change, students were expected to identify the transformation that took place and know a new substance was formed, not just a different form of the same substance. Fifteen percent of the students questioned showed some understanding of chemical change. Fifteen percent had some understanding of chemical change but then provided evidence of a physical change, and some said the change was not a chemical change because no chemicals were involved. Seventy percent of the students showed no understanding that a chemical change had occurred with the burning of the candle and formation of the black film on the glass rod.

Suggestions for Instruction and Assessment

  • This probe can be used with the card sort strategy (Keeley 2016). Print each of the answer choices on cards. In small groups, students sort the cards into two columns: changes in which new substances are formed; changes in which new substances are not formed. As they sort, they discuss their reasons for placing each card. This strategy gives students the opportunity to explicate their reasoning for each example.
  • A related precursor probe for grades K–2 students is “Back and Forth” (available in Keeley 2013), in which students determine which types of changes in matter can change back to their original form and materials.
  • Combine this probe with understanding what a substance is. Whereas in science the word material is very broad, the word substance has a more specific meaning. Students tend to use the word substance synonymously with the word material. A substance in science is defined as a homogeneous type of matter having a definite chemical composition (Driver et al. 1994).
  • Ask questions such as the following: “What properties of this changed material are different from the original material? What properties are the same? Can you get the same material back again?”
  • Students should see a great many examples of reactions between substances that produce new substances that are very different from the original reactants. Start off with examples of familiar reactions such as burning sugar, adding baking soda to vinegar, and rusting to determine whether new substances are formed.
  • Help middle and high school students see that the rearrangement of atoms can be used to explain new substances formed from chemical reactions and that this is an example of another way that the atomic/ molecular theory can be used to explain a wide variety of matter phenomena.
  • To determine whether a new substance is formed, students should have opportunities to carefully compare the substance or substances after a change has been made to the original matter and compare it to the substance or substances they started with before the change.
  • The Framework (NRC 2012) deemphasizes the difference between physical and chemical changes. It suggests that instead of using the term physical change, students should compare the properties of the material before and after the change and have them describe the type of change: for example, chemical reaction, phase change, dissolving, or formation of a mixture (Mayer and Krajcik 2017).
References

Abraham, M., E. Grzybowski, J. Renner, and E. Marek. 1992. Understandings and misunderstandings of eighth graders of five chemistry concepts found in textbooks. Journal of Research in Science Teaching 29 (2): 105–120.

Abraham, M., V. Williamson, and S. Westbrook. 1994. A cross-age study of the understanding of five chemistry concepts. Journal of Research in Science Teaching 31 (2): 147–165.

Ahtee, M., and I. Varjola. 1998. Students’ understanding of chemical reaction. International Journal of Science Education 20 (3): 305–316.

Driver, R., A. Squires, P. Rushworth, and V. Wood-Robinson. 1994. Making sense of secondary science: Research into children’s ideas. New York: RoutledgeFalmer.

Keeley, P. 2013. Uncovering student ideas in primary science, volume 1: 25 new formative assessment probes for grades K–2. Arlington, VA: NSTA Press.

Keeley, P. 2016. Science formative assessment, volume 1: 75 practical strategies for linking assessment, instruction, and learning. 2nd ed. Thousand Oaks, CA: Corwin Press.

Mayer, K., and J. Krajcik. 2017. Core idea PS1: Matter and its interactions. In Disciplinary core ideas: Reshaping teaching and learning, ed. R. Duncan, J. Krajcik, and A. Rivet, 13–32. Arlington, VA: NSTA Press.

National Research Council (NRC). 2012. A framework for K–12 science education: Practices, crosscutting concepts, and core ideas. Washington, DC: National Academies Press.

Stavridou, H., and C. Solomonidou. 1989. Physical phenomena–chemical phenomena: Do pupils make the distinction? International Journal of Science Education 11 (1): 83–92.

Vogelezang, M. 1987. Development of the concept of “chemical substance”: Some thoughts and arguments. International Journal of Science Education 9 (5): 519–528.

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