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 freezing point. The probe is designed to find out if students recognize that the temperature at which water freezes is independent of the volume.

Opposing views

Freezing point, melting point, characteristic properties, intensive properties, temperature, properties of matter

The best answer is Devon’s: A large block of ice freezes at the same temperature as the small ice cubes. It may take longer to freeze the block of ice, but the temperature at which pure water begins to turn to ice (its freezing point) is 0°C. It is the same temperature at which a solid (ice) begins to melt (its melting point). Except for unusual situations, such as supercooling of liquids, melting point and freezing point are usually the same. This temperature is the same, regardless of how much water is being frozen or how much ice is being melted. Freezing point and melting point are characteristic properties of matter that are independent of the amount of matter. Each pure substance has a specific freezing or melting point under standard conditions.

Elementary Students

At the elementary level, students’ experiences with the properties of materials are primarily observational. The idea of change is connected to physical properties by subjecting materials to heating and cooling and observing what happens. In the primary grades, students become familiar with the change in states of water from solid to liquid and liquid to solid. Students learn how to use thermometers to measure the temperature of water. They may observe that water freezes at 0°C or 32°F and connect the temperature of freezing water to weather phenomena.

Middle School Students

In middle school, students shift their focus from general properties of materials to the characteristic properties of the substances. Students learn about the characteristics of different states of matter and the properties associated with phase changes from liquid to solid (freezing point) or solid to liquid (melting point). They also learn that these properties are the same for a given substance under ordinary conditions and can be used to identify substances. Students begin to develop the idea of intensive properties in which a property such as freezing point is independent of the mass or volume of a substance.

High School Students

During high school, instructional opportunities connect the macroscopic properties of substances to microscopic properties. Students can relate the particulate nature of liquids and solids to phase changes. They develop the idea that at the freezing point, particles of the liquid and the solid have the same kinetic energy. Students should be able to explain, using a particle model, why the water freezes at the same temperature regardless of how much water is in the sample. They should also be able to explain why the freezing point and the melting point is the same for pure substances.

This probe is best used with grades 6–12. You may wish to use visual props for this probe, such as a small tray of ice cubes and a block of frozen ice in a container. Be aware that some students may focus on the time it takes the ice to freeze, rather than the temperature. You may need to remind them that the probe is asking for an explanation of how the amount of water determines the freezing temperature, not how long it takes the water to freeze.

• In a study examining Korean students’ conceptions of differing ice cube sizes, the students were asked, ‘‘What will the temperature of ice cubes of two differing sizes be when taken out of a freezer?’’ The percentage of students who thought that larger cubes produce colder temperatures was highest among students ages 4–9. Those students tended to think that temperature is related to material size. Around age 10, students in the study generally thought that size and temperature were unrelated; however, a significant percentage of 11-yearold students (55%) still related temperature to the size of the ice cube (Paik, Cho, and Go 2007).
• Students may use the intuitive rule “more A, more B” to reason what happens when you freeze different volumes of water. Using this rule, students may think that when there is more water to freeze, more “cold” is needed and thus the freezing temperature needs to be lower (Stavy and Tirosh 2000).
• Up to age 12, students are familiar with the term temperature and are able to use a thermometer to measure the temperature of objects or materials but actually have a fairly limited concept of temperature. They rarely use temperature to spontaneously describe the condition of an object. In certain experimental situations, some students believe that the temperature of an object is related to its size. In one study, more than 50% of 12-year-old students thought that “a larger ice cube would have a colder temperature, and hence the larger ice cube would take longer to melt” (Erickson and Tiberghien 1985, p. 61).
• Cosgrove and Osborne (1980) interviewed students about their ideas related to changes in state and noticed that students generally do not regard a change in state as being related to a specific temperature.

Konicek-Moran, R. 2013. How cold is cold? In Everyday physical science mysteries: Stories for inquiry-based science teaching, R. Konicek- Moran, 113–122. Arlington, VA: NSTA Press

Link, L., and E. Christmann. 2004. Tech trek: A different phase change. Science Scope 28 (3): 52–54.

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

NGSS Archived Webinar: NGSS Core Ideas—Matter and Its Interactions, http://learningcenter. nsta.org/products/symposia_seminars/NGSS/ webseminar27.aspx.

Purvis, D. 2006. Fun with phase changes. Science and Children 32 (5): 23–25.

• This probe can be followed up with the science practice of designing and carrying out an investigation. Ask the question, and encourage students to commit to a prediction and explain their reasoning behind their prediction. Then have students test their predictions by placing a thermometer in a small ice cube tray and a large container of water and recording the temperature as the ice forms. The dissonance involved in discovering that the freezing temperature is the same for both quantities should be followed with opportunities for students to discuss their ideas and resolve the dissonance.
• Use two different volumes of water to collect and compare data, starting with a liquid to gas phase change. Begin by graphing two different volumes of boiling water and have students notice that when two phases are present (liquid and gas state), the temperature remains the same, regardless of quantity. Allow the boiling water to cool, and observe that the temperature steadily decreases when only one phase is present (liquid), although the rate of cooling may differ in the two samples. Students can then use their graphs to hypothesize what would happen to the temperature of two different volumes once the water begins to freeze and two phases (liquid water and ice) are present, and they can then test their hypotheses. This investigation allows students not only to observe the patterns during change in state but also to notice that there are constants in the plateaus of these patterns, regardless of the volume of water.
• Explicitly connect the idea of a specific freezing point to a specific boiling point and other characteristic properties in order to develop the generalization that some characteristic properties are independent of the amount of a sample. Once students grasp this idea, introduce the term intensive properties.
• Compare freezing point to melting point to show that when two phases are present, the temperature is the same, regardless of whether you start by melting ice or start by freezing water.
• Be explicit about developing the generalization that freezing point is specific under standard conditions for all pure liquid substances, not just water.
• Connect this probe to everyday weather phenomena students may experience. Does the temperature at which water freezes to sleet or ice change with the amount of precipitation, or is the freezing point the same?