The Sweating Glass and the Stubborn Thermometer · Chapter 24

Learning target: I can record what I notice and wonder about cold containers in a warm room, use what I already know about particles and energy, and write first explanations for where the water on the outside comes from and why ice water stays at 0 °C.

Directions

Read both observations slowly. Study the figure and the table, which show what one class saw. Write what you notice before you write what you wonder. In Part C you will write first explanations. It is fine to be unsure, but give a reason for every idea. Keep this sheet: you will come back to it at the end of the chapter and revise your explanations.

You will need: This worksheet, Pencil

Observation 1: Three containers on a paper towel

On a warm, sticky September afternoon, the classroom air is 27 °C. Ms. Ortiz takes a sealed, unopened can of purple grape juice out of the refrigerator, where it has been chilling at about 4 °C, and sets it on a dry paper towel. Next to it she sets an identical sealed can of grape juice that has been sitting on the counter all day. Then she fills a tall glass with ice cubes, adds tap water, and sets the glass on the same towel. She tapes a small thermometer probe to the side of the cold can. The class watches for ten minutes.

What the class observed. The cans were never opened, and the glass was not overfilled. Temperatures are rounded to the nearest degree.

Observation 2: The thermometer that will not move

Ms. Ortiz stands a thermometer in the glass of ice water and stirs gently every few minutes. The room stays at 27 °C the whole time, so the room is always warmer than the glass. The class records the reading and the ice every ten minutes.

Part A: Notice and wonder

Ice water in a 27 °C room (teaching dataset)
Simulated teaching dataset: the numbers are invented to be realistic, not measured.
Time (min)	Thermometer in the glass (°C)	What the ice looks like
0	0	Glass packed with ice cubes
10	0	Cubes have rounded edges
20	0	About half the ice is left
30	0	A few small pieces float
40	0	One thin sliver is left
50	3	No ice left
60	8	No ice left

1.Write three things you notice in Observations 1 and 2. At least one must compare the cold can with the room-temperature can, and at least one must use a number.

2.Write three questions you wonder about. Start each with why, how, where or what would happen if.

3.By how many degrees did the cold can's surface temperature change in ten minutes? Show the subtraction. Then say which way you think energy moved between the room air and the can, and why.

Part B: What you already know

4.Name the three states of matter. For each one, describe in a few words how its particles are arranged and how they move.

5.Water can be an invisible gas called water vapor. Name two places the water vapor in a classroom could come from.

Part C: Your first explanations

Three students offered ideas about the drops. Ari: 'The juice is seeping out through tiny holes in the metal.' Bea: 'The cold from the can turns into water when it touches the warm air.' Cy: 'Something invisible in the air turns into water when it touches a cold surface.'

6.Test each idea against the observations. In each cell, name a specific observation from the figure or the text. Write 'none' if you cannot find one.

One observation that fits this idea	One observation that does not fit this idea
Ari's idea
Bea's idea
Cy's idea

7.Write your best explanation so far. Where does the water on the outside of the cold can and the glass come from, and why does none form on the room-temperature can? Use the word energy at least once.

8.Look at the table in Observation 2. Energy should be flowing from the 27 °C room into the glass the whole time. For the first 40 minutes the reading did not rise. What do you think that energy was doing? What happened as soon as the ice was gone?

9.Describe one test the class could do to check one of your explanations. Say what result would support it.

Keep this page — At the end of the chapter you will reread q6, q7 and q8 and mark what you would keep, change or add. A first explanation that changes is a sign of learning, not a mistake.

Starters and a particle reminder

For q7, try: 'I think the water comes from ___ because ___.' 'It only forms on cold containers because ___.' For q8, try: 'The energy could be going into ___ instead of ___.' Reminder: particles in a gas are far apart and move fast; particles in a liquid are close together but slide past one another; particles in a solid are held in place and vibrate.

Colder than freezing

Suppose the can came out of a freezer at −15 °C instead of a refrigerator. On a humid day, a white, fuzzy coating forms on it instead of clear drops. Predict what the coating is made of and which state the water skipped on its way there. Then explain why a freezer-cold can is more likely to get this coating than a refrigerator-cold can. You will learn the name of this change in the chapter; for now, describe it in your own words.