Evaporation & Condensation in a Solar Stillschwarz.wiki.educ.msu.edu/file/view/EvapCondTeacher Guide2011.pdf... · Rubber band Water Food coloring ... Imagine that you are lost in

© 2011 Written by: Hamin Baek and Christina Schwarz (Michigan State University), in collaboration with Carrie Beyer (University of Michigan), Lisa Kenyon (Wright State University), and middle school teachers Paul Hinze and Jocelyn Mankowski (Okemos 5-6 school). This research was funded by the National Science Foundation under Grant ESI-1020316 to the Scientific Practices project at Northwestern University and ESI-0628199 to the MoDeLS project at Northwestern University. The opinions expressed herein are those of the authors and not necessarily those of the NSF.

“Would You Drink the Liquid in the Bottle Cap?”

Evaporation & Condensation in a Solar Still

Teacher Guide

Your Students’ Grade ____

Your Name ______________________

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Starting Date (mm/dd/yyyy) ____ / ____ / _______

Ending Date (mm/dd/yyyy) ____ / ____ / _______

Learn Science by Doing Science! Evaporation and Condensation

Teacher Guide Page | 2

Prior to Lesson 1

Before Beginning

GET READY

Materials and equipment • To set up the two-cup experiment (See a picture below), you need:

○ Two identical cups – plastic, glass, or any other transparent cups ○ Plastic wrap or a slide of glass – to cover a cup ○ Marker – to mark water levels over time

Teacher preparation

• Before Lesson 1, set up the two-cup experiment that you will use later (Lesson 3) when students conduct their empirical investigations about evaporation. Place two cups on the front table so that all the students can see. [Alternatively, you could have your students (each individual or group) set up their own sets.] Put the same amount of water in each cup and mark the water level. Leave one cup open and the other covered with a plane of glass or plastic wrap (see a picture below). Tell students not to touch the set because it may affect the result.



Lesson 1

Introduce a Solar Still GET READY

Objectives of the lesson

• To develop an initial hypothesis about what is happening to the water in a solar still as it evaporates, condenses, and collects in a bottle cap and why.

Materials and equipment

• You need the following for making one solar still: (Note: You need a solar still for each group and preferably for yourself. Get enough materials to supply one for each student group.) ○ Clear two-liter bottle with top removed ○ Two popsicle sticks ○ Bottle cap ○ Rubber cement (or other type of glue) ○ Plastic wrap ○ Small weight or marble ○ Scissors ○ Rubber band ○ Water ○ Food coloring (and other supplies to make water dirty such as coffee grounds, etc.)

Teacher preparation

• Make solar stills as instructed on Student Notebook (hereafter SN) p. 2.

IN CLASS

Introduce the whole unit briefly. You could emphasize that students will learn science as they do what scientists do to study natural phenomena. This will be interesting (and maybe even fun!) as they will get to think about some phenomena, do some investigations and test out their ideas.

OVERVIEW 1. In this lesson, you will be introduced to a solar still. Then, you will think about some of the

interesting things that are happening inside the solar still. Introduce this lesson as in SN. SOLAR STILL 2. Imagine that you are lost in desert (like in the TV show Survivorman) or out at sea. How could you

find water to drink since the ocean is composed of salt water? There is a simple, low-tech device for getting drinkable water from sea water or water absorbed in the ground. It’s called a solar still. We will investigate the things happening (or phenomena) inside a solar still. Understanding this process could someday save your life or others’ lives!

Ask students, “Imagine that you are lost in desert or out at sea (like the Survivorman). How could you find water to drink since the ocean is all salt water?” and engage with students’ responses to some extent. You could also ask if students or someone they know had a similar experience. This is an important step for motivating students in this whole unit.



Introduce a solar still as written in SN and using various images and video clips in the folder of “Multimedia resources.”

Talk about various types of solar stills and how and where they are used.

3. There are various types of solar stills for various purposes. But, you can easily make one as follows (See Figure 1). • Cut a plastic bottle as shown in (a). • Make slits for craft sticks as shown in (b). • Make dirty water (e.g., Mix coffee or food coloring with water). • Pour the dirty water into the bottle as shown in (c). • Insert two craft sticks through the slits as shown in (c). • Attach the bottle cap to the sticks with glue as shown in (c). • Place the plastic wrap loosely over the top of the bottle, and secure it around the bottle with a

rubber band as shown in (c). Let the loose excess plastic hang down inside. • Depress the loose plastic with a weight so that the lowest point is over the catch pan as

shown in (c).

Figure 1. A procedure of making a solar still

Describe how to make a solar still as in SN.

DRIVING QUESTIONS ABOUT THE SOLAR STILL PHENOMENON 4. Your teacher will give a solar still to each group. As a group, observe what happens inside and

outside your solar still. Distribute solar stills to each group. Make sure you put warm dirty water and a cold marble for each solar still to quicken

the process of evaporation. [Note: Heat serves the role of increasing the rate at which water molecules escape from the surface of the dirty liquid. Additionally, using a cold marble will quicken the process of condensation by creating a larger temperature difference between the air in the solar still and the object (marble) on which the water vapor will condense.]

5. Think about the next questions and write down your initial thoughts under each question. • What changes did you observe over time? • How and why do you think these changes happened? • How do you know?

Throughout the unit, students will be asked these three questions repeatedly. See Note 1 below what these questions

are for. These questions are also related to four crucial dimensions of scientific practices (Note 2).



Observation, explanation, justification

• The first question has to do with observation. Observing a target phenomenon using our senses and instruments is a fundamental scientific activity. This question is intended for students to engage in making observations. Students may tend to name a process (e.g., “evaporation”) in answering this question. Guide them to avoid this sort of conceptual terms and make specific observational statement. You could ask them, “What did you actually sense (see, hear, smell, feel) using your eyes, ears, noses, hands, and instruments (if applicable)?”

• The second question asks students to present their explanation of this phenomenon. Students may bring all different kinds of explanations at first. We anticipate, however, that they can give scientific explanations (e.g., presenting processes or mechanisms) as they become increasingly familiar with this practice.

• With the third question, students are challenged to justify their explanation. This process includes evidence and reasoning. In both scientific and everyday contexts, argumentation is a crucial part of scientific literacy required of citizens living in the 21st century. Students need to learn to support their claim (or their explanation in this case) with solid evidence and sound reasoning that links that claim to the particular evidence. Although evidence can refer to various things, scientific communities have embraced empirical evidence as an important source of scientific knowledge. This question aims to nurture this habit in students’ minds.

Note 1. Observation, explanation, and justification Four crucial dimensions of scientific practices (G.A.M.E)

• We propose that scientific practices such as modeling and explanation involve four interrelated but conceptually/analytically distinct dimensions. They include: ○ Generality: Generality has to do with the generality of the model, explanation or argument. Generality is very

important in science as it gives power for predicting other phenomena in the world. Learners may make models or explanations just to explain or predict a particular phenomenon but then learn to make their models or explanations more general in order to predict multiple phenomena.

○ Audience/communication: This dimension is concerned with the degree to which one is aware of audience as he or she engages in a scientific practice. As one becomes more experienced in a scientific practice, he or she increasingly thinks about what might be important and persuasive to others, and then use that information to inform and improve ideas in the argument or explanation for themselves and others.

○ Mechanism: This has to do with how one explains a phenomenon in a scientific practice. For a scientific practice to be able to generate scientifically meaningful and powerful explanations, it must have some explanatory element that not only describes what happens but also how and why that happens. Strong models and explanations can provide generative and precise mechanisms.

○ Evidence: Knowledge generated from any scientific practice is supported by some sort of authoritative source of that knowledge. Strong models and explanations are supported by tested information from the world (empirical evidence) and other previously derived and tested scientific theories and ideas.

• As one engages in (e.g., constructing, evaluating, revising, using, etc.) scientific practices and produces related artifacts (e.g. written explanations, scientific models) as a result, their practices and artifacts reflect all these four dimensions one way or another.

• As one becomes increasingly sophisticated in any scientific practice, so do these dimensions reflected in their practice and artifact.

Note 2. Four crucial dimensions of scientific practices

In this particular context, you could add more questions to each question above to help students make sense of the purpose of each question. A. “What happened to the dirty water, inside and outside of the bottle, the plastic, and the bottle cap?” B. If some students notice that liquid appeared in the bottle cap, “Where did it come from?” If some say that the liquid

in the bottle cap came from the dirty water, you might ask, “Are you sure? How do you know?” “Could you see the movement of the liquid from the dirty water to the bottle cap?”



C. “How do you know that your explanation of how and why the changes happened is correct?” “Do you have any experience, evidence, or information that supports your explanation in B? If so, tell us what they are and how they support your explanation.”

Ask students to write down their thoughts under each question. And say, “We will come back to these questions at the

end of this unit. You will see how you will learn about these ideas and those ideas will improve throughout the unit.” 6. Would you drink the liquid in the bottle cap? Why or why not?

For the rest of the unit, you will work on understanding what is going on in the solar still to find out whether or not you could drink the liquid in the bottle cap.

Based on what students responded to the three questions above, have them make a decision on this issue and provide their rationale. Evidence-based and principle-based decision making is important for all learners. It always involves uncertainty because the information we need to make a decision can never be fully obtained and because there are different perspectives for the same information. Therefore, it’s important to give students practices in making a reasonable decision based on the information available.

Because there is limited information about the solar still, some students might say that they cannot decide at this moment. In particular, students are rightfully concerned about toxic chemicals that might be in the dirty water. You could ask students their reasons which might lead a brief but productive discussion on the complex process of decision-making. Alternatively, you could ask, “What do you need to know and do to be able to answer the questions about the liquid in the bottle cap and how it got there (without tasting the liquid)?” Some examples of students’ responses to the last question may include: • Know how the solar still was designed • Know what the dirty water is made of • Examine the liquid in the cap (e.g. taste, smell, etc.) • Know if the liquid in the cap came from the dirty water • Know how liquid evaporates • Know how gas condenses

Keep track of these ideas and tell students that they will find out the answers to these questions at the end of this unit by investigating evaporation and condensation processes in particular.

HOMEWORK 7. Scientists use models as tools for studying natural phenomena. To understand the phenomenon in

the solar still, we will, like scientists, use models through this unit. Before engaging this practice, it is helpful to have some understanding of what they are. So, read the next passage about scientific models before the next lesson.

Have students read “Scientific Models” on SN pp. 4-5 as homework.

Conclude the lesson by announcing what students would do/learn in the next lesson.



Lesson 2

Construct an Initial Model of Evaporation

GET READY

Objectives of the lesson • To come up with their initial ideas about what happens to a liquid when it comes in contact with air over an

extended time period and how and why that happens. • To construct an initial model of evaporation. • To become familiar with the modeling practice of ‘construct.’

IN CLASS

SCIENTIFIC MODELS 1. Review what you read about scientific models as homework. As a class, discuss key ideas and

features about them. Also talk about why using scientific models is important in understanding how and why natural phenomena work.

Scaffold students’ discussion about models and scientific models. The following sequence is one suggestion. If you run short of time, you could just focus on scientific models. • Say that science has a particular kind of definition for a model. Ask, “What are scientific models?” and engage with

students’ responses. Ask students to compare and contrast different scientific models and their purposes. • Introduce what scientific models are using the following descriptions in Note 3. • Say that scientists construct, evaluate, revise, and use scientific models in studying natural phenomena to be able

to explain and predict the world. As learners about the world, they can do the same which will help them better understand things like what is going on with the solar still.

What are models? • A small copy of an object • An example for imitation • An idealized representation • A person employed to wear clothing for purposes of display and advertising • A style or design of a particular product

What are scientific models?

• A scientific model is a representation that simplifies an event in the natural world in order to highlight its main parts. For example, a scientific model can represent something that is too small or too big to see with your own eyes. Examples of scientific models include the model of the water cycle, models of food webs in ecosystems, and a model of light traveling as ‘light rays.’

• Scientific models include (1) the main parts of the event, (2) the relationships among those parts, and (3) the rules for how the model works. For example, in the water cycle model, the parts might include water, land, and sky. The relationships might include how the water in the lakes and oceans is related to the water in the sky, and the rules might include how the water moves between the lakes and clouds.

• The two-fold purpose of scientific models—to generate explanations and predictions—make scientific models different from other kinds of models



• People can create models with pictures, words, mathematical equations, and computer programs. Note 3. Models and scientific models

OVERVIEW 2. To better understand the phenomenon in the solar still, we will break our investigations into two

parts and study them in order. In this lesson, you will try to understand the first process – evaporation – by constructing your initial model of it.

Present the overview of the lesson as in SN.

EVAPORATION PHENOMENA 3. In the solar still you observed before, some of the dirty water disappeared. In the next several

lessons, we will investigate this phenomenon in more depth. Make a bridging comment (from the solar still to evaporation) as in SN. 4. Look at the two pictures below and answer the following questions.

Figure 2. Water on a puddle on the ground Figure 3. Hand sanitizer

• How are these two phenomena different? • How are these two phenomena similar? • Can you think of other phenomena that are similar to these two?

Have students look at Figure 2 and 3 and ask students what they notice. To facilitate this conversation, you could ask, “What changes do you see between “before” and “after” in each figure?” Engage with students’ responses as well as questions about the figures. • Some information about Figure 2

○ The line was drawn to show the contour of the water more clearly. ○ The ground is covered by asphalt.

Have students compare the two phenomena and individually write down their answers to each question.

Have students share their answers. You may want to record students’ responses on the board as they share their ideas

and engage with these responses. 5. In all these phenomena, liquid disappears into the air over time. This process is called

evaporation. Guide students to note that these are all phenomena in which liquid “seems” to disappear when it comes into contact

with the air over time. You could mention other phenomena of evaporation in addition to what students already mentioned such as: • Dishes drying • Nail polish drying • Perfume drying



• Paint drying • Sweat drying • Marker drying • Hand sanitizer drying

DRIVING QUESTIONS ABOUT EVAPORATION 6. Here are crucial questions we will focus on to understand evaporation. They seem simple. But

they are a lot more complicated and important than you might think! Answer these questions below. A. What changes did you observe over time? Where did the liquid go? B. How and why do you think those changes happened? In other words, how and why do you

think the liquid seemed to disappear? C. How do you know?

Remember that these questions are basically the same questions that they saw before and about observation, explanation, and justification respectively (Note 1). Help students to note these emphases and individually write down their answer to each question.

CONSTRUCT AN INITIAL MODEL OF EVAPORATION 7. Construct your initial model of evaporation in the box on the next page. It will help you think

about and understand evaporation. You can choose any phenomenon of evaporation for constructing your model.

Tell students that they are about to participate in one element of the modeling practice called model construction. Briefly explain what this is about using Note 4. • One way to help students learn about the modeling practices is to create a chart that you can display in the front of

your classroom. In this chart you can record the different elements of the modeling practice—construct, use, evaluate, revise—as the students experience them during the unit and refer back to the chart as students revisit the elements of the modeling practice.

Have students construct their initial scientific models of evaporation in their SNs. Tell them to attempt to reflect their

answers to the driving questions above in their models. • To help students construct their initial models, consider using some of the following instructional strategies:

○ Have students first create a picture or simulation in their heads of what they think happens to the liquid in their chosen phenomenon before having them draw their models on paper. This will help students see that creating an initial model is not just an exercise in creating artwork. This may also help them see that there is a difference between their idea model and their expressed model.

○ Have students think about what the main parts they should include in their model as well as the characteristics of and relationships among those components. You may also want to have students share their ideas about these components and record them on the board. Eliciting their ideas before having them express them on paper will help students produce models that reflect their complete initial understandings of the phenomenon.

○ One important feature that students should include in their initial models is the idea that the event takes place across time. Students can depict change over time, for example, by drawing a ‘before—during—after’ picture like in a comic strip or cartoon. (Note: Besides showing change over time, other aspects of a comic strip or cartoon are not particularly relevant for constructing models.)

○ Another important feature for students to include in their models is a ‘mechanism’ that explains what is happening to the water. Asking students to include this feature enables students to articulate their reasoning for how the water is changing over time rather than just having them provide a description of the change.

What is model construction? • When students develop initial models, they are engaging in the modeling practice of construction. Constructing



8. Explain your chosen phenomenon of evaporation using your model in your group. All the members do this one after another.

9. As a group, discuss what are similarities and differences among different models. While doing

this, you could also talk about some of the following questions. • Why did you choose that phenomenon for your model? • What are things you included in your model? What are things you didn’t include in your

model? Why did you do that? • How did you show how and why the phenomenon occurs in your model?

After students finish constructing their initial models, have them explain their chosen phenomena of evaporation using their models in their group. Let them know that they need to answer the driving questions in their explanation.

As (or after) students share their initial models in their group, have them ask one another the questions suggested above in SN No. 8. Walk around and help each group to have a meaningful and productive discussion. While doing this, consider the four dimensions of scientific practices (Note 2). For example, you could ask questions as follows: • Generality: [If a student included information specific to his/her chosen phenomenon and not relevant to

evaporation in general] Ask that student “Why did you include particular information? Do you think it is important or necessary in explaining this phenomenon?”

• Audience/communication: [If a student’s representation is unclear of they did not include any communicative features like labels] “What is this? What is that?” [After the student’s response] “Are there any ways that help others understand what you want to show? Does your model show the idea you want to express?”

• Mechanism: The third question concerns this. • Evidence: At this moment, not many students will include evidence such as data or measures from a particular

instrument. Nevertheless, when you find a model that includes evidence of any sort, encourage the student. (Go to page 11 to see what evidence is.)

[Optional] After the group discussion, you may want to lead a class discussion on the same questions in SN No. 8. Have

each group share what they talked about and write down those ideas on the board. Compare and contrast different ideas and ask them relevant questions.

Conclude the lesson by telling students:

• “How do you know that your model is correct? No matter how great a model appears, we can’t say it is a good model unless it is supported by evidence. In the next lesson, you will conduct experiments to come by evidence and will test your initial models and the ideas behind those models using the evidence.”

scientific models helps us explain and predict familiar phenomena to ourselves and other people. In constructing a model, we first uncover our existing ideas about the central features of the phenomenon that we are trying to understand better. This is our idea model—our personal understanding of how a phenomenon works as visualized in our heads. We then develop a representation that captures our existing ideas about how to explain or predict the phenomenon. This representation of the idea model is referred to as the expressed model and can take the form of pictures, words, physical objects, or even equations.

Why engage students in this modeling practice?

• Having students construct their own models enables them to become aware of their own ideas about a scientific phenomenon as well as other students’ ideas. It also provides students with a starting place for engaging in the process of scientific modeling. Finally, having students construct models gives you, as the teacher, the opportunity to learn about and assess students’ initial ideas about the new content that you are studying.

Note 4. Model construction



Lesson 3

Empirical Investigations of Evaporation

GET READY

Objectives of the lesson • To conduct a variety of empirical investigations in order to test their initial models of evaporation. • To evaluate their initial models based on consistency with empirical evidence. • To become familiar with the modeling practice of ‘evaluate.’ • To become familiar with the evaluation criterion of ‘consistency with evidence.’


• Experiment 1: The two-cup experiment already set up from the beginning of the unit • Experiment 2: One humidity detector, one container (hood), a beaker, water (warm water preferred), a clock (to

measure time) • Experiment 3: Two humidity detectors, two containers (hoods), two identical beakers, warm and cold water, a clock

(to measure time)

Teacher preparation • Set up stations for these experiments.

IN CLASS

OVERVIEW 1. No matter how fantastic you model may look, it is just a creative drawing unless it is supported by

information and ideas about what actually happens in the world. In this lesson, you will do some experiments to test your model. If your model passes these tests (if it helps explain what happens and is consistent with what happens), you could say your model is pretty good. If it doesn’t, you can get some ideas to make it better.


EVIDENCE 2. As a class, talk about evidence in general using the following questions.

• What is evidence? • Why is evidence needed for models? Do you need to show evidence in your models? • How do we get evidence?

Facilitate discussion about evidence using the questions above. As engaging with students’ responses, help them to note: • Evidence is information or data that support a claim. In science, it can take various forms including observations,

numerical data, and established scientific facts. • Evidence is needed to support or justify models. But, evidence alone is not enough. Sound reasoning that links

evidence to a model is also needed. • You do not need to include evidence in your models. But, your models must be consistent with evidence. Including

evidence in your models is sometimes helpful for others to see the validity of your models.



• As noted above, evidence can take different forms. But, carefully designed empirical investigations are important venue to generate evidence.

BRAINSTORM EXPERIMENTS 3. To get some evidence to test our models of evaporation, what kind of tests or experiments do we

need to do? As a class, think of some tests/experiments and talk about those ideas. Write them down below.

Since students had general discussion of evidence (SN No. 2), now help them to come up with ways (tests, experiments) to generate evidence specifically for their models of evaporation. By doing so, they could understand better the relationship between evidence and models (and explanations). Because this is challenging to them, you may need to give them more scaffolding and encouragement than correction.

EXPERIMENTS To help students effectively to conduct the experiments, come by evidence, and evaluate their model based on the evidence, we adopted the following sequence. This sequence is described below: • PREDICT: For each experiment, students will predict what is going to happen based on their model. This requires

deductive reasoning from their general model to a particular phenomenon. If their prediction is correct (and given their deductive reasoning is correct), it means that their model is valid so far. If their prediction is not correct, it means that their model was falsified by the evidence and needs to be revised.

• SHARE: They will share their prediction with their group. This social element will help them to articulate their prediction.

• OBSERVE: They will observe what really happens using their senses (e.g., see, hear, smell, feel) and instruments (e.g., a humidity detector). The result of their observation can be numerical data (if they measured length, mass, etc.) or observational statements.

• PATTERN: They will find a pattern from their data. A pattern is a sort of generalization. For example, from the data of X=10g (0 second), 20g (5 second), and 30g (10 second), they should be able to say, “The mass of X increases over time.” This pattern serves as empirical evidence.

• EVALUATE: They will evaluate their model using the evidence. By comparing their prediction and the evidence, they should be able to see whether or not their model is valid. The first two sentences – “What does the result mean about what happened to the water in the cups? How and why do you think this happened?” – are provided to help them do this comparison. Refer to Note 5 below.

• REVISE: When they find a discrepancy between the evidence and their model, they need to think about how to revise their model.

What is model evaluation?

• When students evaluate their initial models, they are engaging in the modeling practice of evaluation. In evaluating models, we identify strengths and limitations with our idea model in order to determine how well it explains or predicts a phenomenon—in other words, how well it meets its intended purpose. When we evaluate models, it is helpful to use criteria for doing this. Some of the most important criteria fall into one of the four dimensions of scientific practices as follows: ○ Generality: Good models are general enough to explain and predict multiple phenomena. To this end, good

models do not include irrelevant components of phenomena such as information specific to a particular phenomenon and background objects and therefore represent a phenomenon in an abstract and general manner.

○ Audience/Communication: Good models represent the model constructors’ ideas and are clear for others to understand them. To this end, they include words, arrows, dots, colors, lines, other symbols and communicative tools. Such tools and strategies are also important at clarifying and advancing the designers ideas about the content as well.



○ Mechanism: Good models include a detailed description of a process or mechanism to explain a target phenomenon. They typically include scientifically meaningful and effective explanatory features such as invisible entities (e.g., particles, energy, force), their behaviors and relations with other entities, scale change, and time elapse.

○ Evidence: Good models are consistent with and supported by multiple pieces of empirical evidence and general scientific principles and information.

Using these criteria, one can evaluate his/her own models or others’ models.

Why engage students in this modeling practice? • Having students evaluate their own models helps them recognize that all models aren’t created equal and that

some are better than others. Additionally, students are able to engage in meaningful revision of their models. Note 5. Model evaluation

EXPERIMENT 1: AN OPEN CUP AND A COVERED CUP 4. To explain what happens to the water in the puddle, some might think that the water seeps down

through the ground. To test this idea, let’s think about the two cups your teacher set up a while ago – an open cup and a covered cup both containing water.

You might want to check how many students think the same way. Ask those students about their reasons for their thoughts. • In the case of the puddle on the ground, some students might notice that the ground has lots of small holes. Then

you could say like, “This is an idea about evaporation in general, which is that liquid seeps through the container. But in the case of the puddle on the ground, you might be right. To see whether it is the case or not, how would you change this experiment?”

5. [PREDICT] Predict what the water levels in the cups will be if the water seeps down through the

cups. Draw your prediction on (A) of Figure 4. Next, write down your explanation in the box and draw your prediction on (B) of Figure 4.



Figure 4. An open cup and a covered cup

For the idea of water seeping through the cups, students may have difficulty predicting the result. You could add, “For both cups, suppose that water seeps through the container at the same rate because the two cups are identical” to help them to predict better.

To give students some ideas of how to predict from their own model and explanation, you could exemplify a few predictions. One example is a model/explanation that water vanishes.

6. [SHARE] Share your prediction and reason with your group. After this, you could ask some of them to share their predictions and reasons with the class. Engage with these ideas in

order for the class to see the relationship between models and prediction.

7. [OBSERVE] Make an observation of the two cups. Draw what you observed about the water levels of the two cups on (c) of Figure 4.

Have them write down other observations. • Some students may notice that there are water drops on the lid (or plastic) of the covered cup and that the water

level in that cup was lowered a bit. Depending on other students’ interest and level of understanding, decide to lead conversation on it further or delay it until the section of condensation.

8. [EVALUATE] What does the result mean about what happened to the water in the cups? How and why do you think this happened? Evaluate your own model on the basis of this evidence. Can your model explain this evidence or not? Why or why not? Write down your evaluation in the table at the end of this lesson (Table 1).

Evaluating one’s model on the basis of evidence is challenging for students. First, ask students to think of the best explanation/model for the evidence and compare it with their own explanation/model. Second, ask them try to explain the evidence with their own explanation/model.



9. [REVISE] While evaluating your model, what idea(s) did you have to make your model better? Make a note of how to revise your model in Table 1.

When their model failed to explain the evidence, they need to write down how to revise their model.

EXPERIMENT 2: HUMIDITY IN THE CONTAINER - WATER 10. A humidity detector is a sophisticated device to detect humidity in the air. Humidity is a measure

of the amount of water in the air. In this experiment, you will place a cup of water under a covered container and use a humidity detector to measure the humidity in the container over time (Figure 5).

Figure 5. Humidity in the container - Water

Introduce what humidity is as in SN. This is a good time to introduce the term ‘water vapor’ if students are not familiar with this term.

Introduce students to the Pasco humidity detector as follows: • You do not need to explain how the humidity detectors work. • To help them become familiar with the humidity detector, have them inquire the following questions using the

detector: ○ What does the number on the detector mean? ○ What is the humidity of the room? ○ What is the humidity when you breathe into the humidifier? ○ How does the humidity change as you move it close to or far away from a humidifier?

• For more information about Pasco humidity detectors and curricula using them, check out http://www.pasco.com/home.cfm.

11. [PREDICT] Write your prediction below about what you think is going to happen to the humidity

in the container over time. Also explain why you think so.

I predict that the humidity in the container will…

because…

increase decrease stay the same Other:

______________________________________

___________________________________________________________________________________________________________________________

What students write down below “because” is where students show their deductive reasoning from their model to their

prediction. Guide them accordingly.

Some students might check “Other” and say that the humidity will fluctuate over time. You could engage in a discussion about this idea and their reasoning.



12. [SHARE] Share your prediction and reason with your group. After this, ask some of them to share their predictions and reasons with the class. Engage with these ideas.

13. [OBSERVE] Measure humidity in each container as described in the table below. Record the

humidity measurements in the table below and write down any other observations you make.

Measuring Point (when to measure the humidity) Humidity (%) 1. Before you place the cup in the container 2. As soon as you place the cup in the container 3. After 20 seconds 4. When humidity does not change any more

Other observations:

Use warm water to facilitate the process of evaporation and to gain a better result.

In the first measuring point, students will realize that water is already in the air. You might want to follow up this observation by asking what this measurement means or where the water came from. This could stimulate a genuine inquiry from students.

You may need to be flexible about the third measurement point. Alternatively, you may want to have students record the humidity every 20 seconds on a separate paper. After the humidity does not change, they could select some of those full data.

For other observations, decide to what extent you will engage in discussion on those observations.

14. [PATTERN] What pattern do you see from your observations? Choose what you think is the correct one.

Over time, the humidity in the container increased. decreased. stayed the same. Other: ______________________________________.

15. [EVALUATE] What does the result mean about what happened to the water in the cup? How and

why do you think this happened? Evaluate your own model on the basis of this evidence. Can your model explain this evidence or not? Why or why not? Write down your evaluation in Table 1.

16. [REVISE] While evaluating your model, what idea(s) did you have to make your model better?

Make a note of how to revise your model in Table 1. Help students to note that the idea of water simply vanishing is not supported by this evidence but that even though the

water from the plate appears to disappear, it becomes invisible by changing its form from liquid to gas.

Some additional questions to ask at this moment include: • “Why can’t we see water in the air when the humidity detector detects it?” • “Where did the water in the air come from?”



• “Given the water came from inside the cup, how did the water become invisible as it moved from the cup to the air?” • “Did your model explain all of these? If not, how will you change it?”

EXPERIMENT 3: HUMIDITY LEVELS OF HOT AND COLD WATER 17. In this experiment, you will place two beakers containing the same amount of water with different

temperatures in two identical covered containers and measure humidity over time in both containers (Figure 6).

Figure 6. Humidity levels of hot and cold water

It might be that some students think that a heat source is required for evaporation to take place and included the heat source in their initial models of evaporation. This experiment is intended to falsify this notion. Additionally, the evidence from this experiment will allow students to see that evaporation takes place faster in higher temperature than in lower temperature.

18. [PREDICT] Write down your prediction below about what you think is going to happen to the humidity in both containers over time. Also explain why you think so.

I predict that humidity in the container with hot water increased… faster than the humidity in the container

with cold water slower than the humidity in the container

with cold water at the same rate as the humidity in the

container with cold water Other:

______________________________________

because…

__________________________________________________________________________________________________________________________________________________________________________________________________________________

19. [SHARE] Share your prediction and reason with your group.

20. [OBSERVE] Measure humidity in each container as described in the table below. Record all the humidity measurements below and write down any other observations.

Measuring Point Humidity (%) in

container with beaker of HOT WATER

Humidity (%) in container with beaker of COLD WATER

1. Before you place the beaker in the container



2. As soon as you place the beaker in the container

3. After 20 seconds

4. When humidity does not change any more

Other observations:

You can decide whether to have students measure humidity for both hot and cold water or in a row.

You may need to be flexible about the third measurement point. Alternatively, you may want to have students record the humidity every 20 seconds on a separate paper. After the humidity does not change, they could select some of those full data.

21. [PATTERN] What pattern do you see from your observations? Choose what you think is the

correct one.

The humidity in the container with the beaker of hot water increased… faster than the humidity in the container with the beaker of cold water. slower than the humidity in the container with the beaker of cold water. at the same rate as the humidity in the container with the beaker of cold water. Other:

_______________________________________________________________________________. 22. [EVALUATE] What does the result mean about what evaporation? How and why do you think

this happened? Evaluate your own model on the basis of this evidence. Can your model explain this evidence? Why or why not? Write down your evaluation in Table 1.


Help students to note that evaporation takes place at various temperatures. Also help them see that hot water evaporates faster than cold water; in other words, heat speeds up the process of evaporation. However, guide them to notice that a heat source is not required for evaporation to take place.



Lesson 4

Scientific Ideas and Simulations of

Evaporation GET READY


• To explore scientific ideas and computer simulations of evaporation. • To evaluate their initial models on the basis of existing scientific ideas and explanatory features of computer

simulations. • To become familiar with the modeling practice of ‘evaluate.’ • To be able to revise their models on the basis of various resources including evidence, scientific ideas, and

computer simulations • To become familiar with the modeling practice of ‘revise.’


• Computer • Projector

Teacher Preparation • Check if the web sites for computer simulations work well. If your school blocks access to any of these sites, find

these files in “Multimedia Files” provided to you. Run all these links or files and think of what to talk about and what not to and other productive comments and questions.

IN CLASS OVERVIEW 1. In this lesson, your teacher will share some scientific ideas and computer simulations of

evaporation. You can use these to improve your own model of evaporation and to improve your own ideas about how and why it happens. Getting a strong understanding of what is going on will help you explain and predict many other related things about the world.

Tell students “Another thing that scientists do to improve their models is to refer to existing ideas and models about the natural phenomena they are studying. They use these ideas and models to improve their own models. However, they do not simply accept all ideas and models. Instead, they choose some parts of them that they think are useful and then integrate those parts into their own models. This is what we will work on today.”

Try to introduce these ideas/models not as correct answers or authoritative sources of knowledge but good resources

available to use for improving their models.

SCIENTIFIC IDEAS ABOUT EVAPORATION 2. Write down notes about the scientific ideas about evaporation that your teacher shared with you. Here are some scientific ideas students need to know about evaporation.



• Conservation of matter: A general principle for most changes that occur in natural world is that matter does not come into existence out of nothing and does not vanish. Simply put, matter is conserved through all changes although its form may change. This is called the principle of conservation of matter. To apply this principle to evaporation, liquid does not vanish but turns into gas during the process of evaporation.

• The particle nature of matter: Matter is made of tiny bits or particles. Each tiny bit is too small to see with our eyes. So, when they are spread apart, we can’t see them. But, when they clump together, we can see them. Each tiny bit also tends to move continuously. And as temperature increases, the speed of their movement increases.

• States of matter: Matter exists in three phases (states): Solid, liquid, and gas. We can explain how matter appears different using the knowledge that matter is made of tiny bits and their tiny bits move continuously. When the temperature is very low, the tiny bits of matter move very slowly to the point that they do not seem to move at all. They then come or clump together, so we can see it as a chunk with a shape. As the temperature increases, the movement of the tiny bits increases, so they spread apart and the space between the tiny bits become larger. Therefore, we can see the liquid but it becomes fluid. As the temperature increases further, the movement of tiny bits is so fast that the bits spread far apart. Therefore, the substance becomes invisible as a gas.

• Evaporation: Because the tiny bits move, some of them spread out on the surface of liquid and even of solid. Again, they are so small that you can’t see them, and so small that they float. When this happens to the surface of water, water (liquid) turns into a gas called water vapor. This process is called evaporation.

[Optional] • Composition of the air: The air is made of a mixture of gases and empty space. You have heard of some of these

gases like oxygen, helium, carbon dioxide, and water vapor. You know that some of these gases are different from each other. For example, when we fill balloons with helium (an invisible gas), our balloons float in the air because helium gas is lighter than other gases in the air. Our air has oxygen in it, a very important gas that we need to breathe to live! The air also has different amounts of water gas or water vapor in it, too.

• Solutions: There are other times when a similar process to evaporation happens. For example, when you pour salt and sugar in a glass of water and stir, the salt and sugar will spread out into the water and you can’t see them. But, you can taste the salt or sugar in the liquid!

Invite students’ questions about any of these ideas and help them to understand them clearly. • Even though understanding terms like “molecule” is not necessary, let students use such terms if they choose to.

3. Evaluate your own model in terms of these scientific ideas. Do you think your model includes these scientific ideas? Why or why not? Write down your evaluation in the table at the end of this lesson (Table 2).

Have students go back to their initial models of evaporation to check whether their models reflected these ideas. You can exemplify how to do this. For example, show them that just describing “evaporated” along with using wiggly arrows does not explain why water becomes invisible when it evaporates.

4. While evaluating your model, what idea(s) did you have to make your model better? Make a note

of how to revise your model in Table 2. When their models did not reflect these ideas, let them figure out ways to do it. Perhaps they will decide to incorporate

tiny bits and their movement in their models.

COMPUTER SIMULATIONS OF EVAPORATION 5. Explore some computer simulations your teacher will show from the websites below. You can also

work with them yourself later. • States of matter

○ http://phet.colorado.edu/en/simulation/states-of-matter ○ http://preparatorychemistry.com/KMT.htm



○ http://molo.concord.org/database/activities/201.html • Changes of state

○ http://www.bbc.co.uk/schools/scienceclips/ages/9_10/changing_state.shtml ○ http://molo.concord.org/database/activities/180.html ○ http://www.footprints-science.co.uk/states.htm

6. Write down notes about what you learned from the computer simulations. It will be helpful to

consider the following questions. When zoomed in, A. What is matter made of? B. What does matter ‘look’ like in each state (solid, liquid, and gas), according to the

simulations? How do particles that make up matter move? C. What happens to the surface of a liquid? D. How does adding heat change what happens to a liquid? E. Do you think this is what matter really looks like, or is this a useful model to help us think

about how matter behaves? Before showing these simulations, have them read the questions in SN No. 6. Tell them that as they see simulations try

to find answers to these questions. • Most of the answers were already addressed when scientific ideas were presented. But, as they see simulations,

they will find more concrete understandings about them.

Show them these simulations. As they see each simulation, ask some of the questions in SN No. 6 and engage with students’ responses. • Some of these websites contain too much information. So you need to decide what to show and to talk about.

As students explore the computer simuatlions, have them write down notes in their SNs about what they learned.

7. Evaluate your own model in terms of these computer simulations. Do you think your model

includes features from these computer simulations? Why or why not? Write down your evaluation in Table 2.

8. While evaluating your model, what idea(s) did you have to make your model better? Make a note of how to revise your model in Table 2.

Have them evaluate and revise their models on the basis of computer simulations as the did on the basis of the scientific ideas.

HOMEWORK: REVISE YOUR INITIAL MODEL OF EVAPORATION 9. Using the evaluations and revision notes you created in Table 1 and 2, revise your initial model of

evaporation. Discuss what model revision is and what it is needed (See Note 6 below).

Have students go back to Table 1 and 2 and see notes of how to revise their models. Some notes are recurrent. So,

have them summarize these revision notes and revise their models based on them. What is model revision?

• When students revise their initial models, they are engaging in the modeling practice of revision. The purpose of revising a scientific model is to change aspects of the idea model, the expressed model, or both so that the model better meets its intended purpose. We can revise our models in one of two ways. In some cases, we may develop a



modified version of our initial or previous model—for example, to make it consistent with experimental evidence by adding new components or changing relationships between components. In other cases, we may decide to develop a whole new model from scratch if our new ideas are completely different our original ideas about the phenomenon.


• Having students revise their own models helps them develop their understanding that scientific models change as we gain more evidence. Additionally, students are able to see the benefits of engaging in scientific modeling if they have the opportunity to see that their revised model is more accurate, consistent, and clear than their original model.

Note 6. Model revision



Lesson 5

Evaluate Each Other’s Model of Evaporation GET READY


• To determine a set of criteria for evaluating models. • To become familiar with the modeling practice of ‘evaluate’ in social environments

Materials/equipment

• Sample models of evaporation (provided)

IN CLASS OVERVIEW 1. In this lesson, after talking about criteria for evaluating models, you will evaluate the other model

in your group and get feedback from the others in your group about your model. Tell students, “You evaluated your models on the basis of empirical evidence, scientific ideas, and computer simulations

in the previous two lessons. These are important things to consider in model evaluation. But, they are just parts of the full list we need to check. This list is called criteria for evaluating models. In this lesson, we will think about these criteria and, using them, evaluate each other’s models.” • For more information about model evaluation, go back to Note 5.

IDENTIFY CRITERIA FOR EVALUATING MODELS 2. What are features of good models? What are things (criteria) we should think about when we

construct, use, and evaluate models? Discuss these questions in your group and write down your group’s evaluation criteria below.

Have students construct criteria for evaluating models in each group. As in SN, highlight that these criteria are used not only for evaluating but also for constructing and using models because a consistent intention across these different elements of modeling is to improve models to better explain/predict natural phenomena. An easy way to bring up students’ ideas about evaluation criteria is to ask them to fill in a blank after “Good models ____________.” Have students clarify in what sense “good models” are “good” and remind them they are interested in “scientifically” good models.

Nevertheless, allow students to come up with diverse ideas at this step.

3. As a class, talk about criteria for evaluating models. As you and your teacher figure out some new criteria, write them in the space below.

At this step, sort out group criteria and add more if not included already. Again, emphasize that they make criteria for evaluating if certain models are “scientifically” good. For example, some students may think that good models should be aesthetically fine. By asking them why that is important scientifically, they may be able to move their focus from this aspect to a communicative aspect of models (which is scientifically valid).

Write down the class evaluation criteria on the board. Make sure the criteria described in Note 5 are included or emphasized.



4. As a class, evaluate several sample models of evaporation that your teacher presents. Have students practice model evaluation using sample models provided to you. PEER EVALUATION 5. In your group, evaluate one another’s models of evaporation. Here’s how you can do this:

someone shares his/her model and the others give the presenter feedback (compliments and wishes) using the evaluation criteria above. Take turns so that everyone may have the opportunity to present their own model and get feedback from the others. Make sure that the evaluators use different criteria. For example, if you have six criteria and there are three evaluators in your group, the first evaluator uses the first two criteria, the second evaluator uses the next two criteria, and the third evaluator uses the last two criteria.

6. When you share your model of evaporation and the others give you feedback, write that feedback down in the table below, listed by each criterion.

Have students evaluate each other’s model using the class evaluation criteria according to the instruction in SN. This element of modeling practice will face a high level of resistance from students if they are uncomfortable with peer evaluation. Therefore, you may need to explain the purpose of this activity as well as a general culture in the scientific community. Also, as in SN, you may need to use such terms as “feedback,” “compliments,” and “wishes” to reduce this resistance.



Lesson 6

Construct a Consensus Model of Evaporation GET READY


• To construct a consensus model of evaporation. • To use the consensus model to explain and predict other phenomena of evaporation. • To become familiar with the modeling practice of ‘use.’

IN CLASS

OVERVIEW 1. In the previous lessons, you learned many things about evaporation and modeling. In this lesson,

your group will construct a consensus model of evaporation that reflects all of what you as a group have learned. Then, your group will try to explain other evaporation phenomena using your group consensus model of evaporation.

Say as in SN.

You could ask students to share what they have learned about evaporation and modeling.

You might also want to discuss with students: • What is consensus? • What is a consensus model?

Tell students, “After coming up with different models to explain a natural phenomenon, scientists often try to construct a consensus model that integrates all of the best parts of the individual models. This is what will we do. Each of you has your own model that explains what happened to the water on the plate. We will use the best parts of these models to construct a consensus model of evaporation. At the same time, we will need to refer back to the list of criteria that we just developed to make sure that our class consensus model meets all of these criteria.”

CONSTRUCT A CONSENSUS MODEL OF EVAPORATION 2. Your group will construct a consensus model of evaporation based on each member’s second

model. Use your class criteria for evaluating models to determine what parts should be included in the consensus model and how.

Review the class criteria for evaluating models.

Have each group talk about what parts from each member’s model to include in the consensus model and how to do it. • Alternatively, you could facilitate a whole class discussion on this as follows.

○ Ask students which components they want to include in the consensus model. ○ Write them down on the board. ○ Point to some discrepancies among some components and lead a discussion to resolve them. ○ Ask students if they are related to the evaluation criteria. If there is any component that is not related to or

inconsistent with any evaluation criteria, lead a discussion to resolve it.



Have each group construct its consensus model of evaporation.

USING THE MODEL TO EXPLAIN OTHER EVAPORATION PHENOMENA 3. As a class, make a list of other phenomena that might involve evaporation. Each group will

explain one or two of them using its consensus model. Talk about using models to explain and predict other phenomena (See Note 7 below). Here you could remind students

that models need to be general in order to be useful for many phenomena. What is model use?

• When students use their models to explain and predict related phenomena, they are engaging in the modeling practice of use. The purpose of using a scientific model is to generate new ideas (models as sensemaking tools) and to share these ideas with others (models as communication tools). After constructing (or revising) a scientific model, we use models to illustrate, explain, or predict systems or phenomena. These distinctions reveal the kind of thinking the model is being used to accomplish. We often use models to illustrate systems or phenomena that are too difficult to observe directly. For example, we use models to illustrate phenomena that happen on too large or small a scale, cannot be manipulated, or happen very quickly or very slowly. We also use models to explain systems or phenomena or predict outcomes—to theorize what the results might be when new experimental conditions or variables are considered (or when a new phenomenon or event are encountered).


• Having students use their models to explain a particular phenomenon or predict new phenomena helps them develop an understanding of the purposes of scientific models. It also helps students develop their ability to engage in scientific modeling.

Note 7. Model use Together with students, make a list of other evaporation phenomena. Assign them to the groups evenly. These

phenomena include: • Perfume drying • Wet dishes drying • Wet hair drying • Hand sanitizer drying • Nail polish drying • Paint drying • Sweaty skin drying

4. Here is a suggestion for how to do this. First, try to match your consensus model to the

phenomenon. What parts of your consensus model are like the phenomenon you are trying to explain? You will find that matching works well for some parts but not so well for the other parts. Second, based on the well-matched parts, “run” this model in your head to imagine what is going on with the phenomenon. Finally, make sure this simulation (“run”) can explain the phenomenon. If it cannot, you need to go back to the previous steps and fix any errors or problems. If it can, show how your model explains the phenomenon in the box below. • Evaporation phenomenon 1: _________________________ • Evaporation phenomenon 2: _________________________

Explain how to use a consensus model to explain other phenomena.



• If students have difficulty with understanding how to do this, you may need to do this for an evaporation phenomenon.

Have each group use its consensus model to explain its assigned evaporation phenomena.

5. Share how your group used your group’s consensus model of evaporation to explain the

phenomenon to the class. After each group finished using its model, have each group share how it did it with the rest of the class.

After each group finished sharing how it used its model, ask students questions such as:

• What are your compliments and wishes for how the other groups used their models? • What similarities did you notice among these ways of using models? • What differences did you notice across these ways of using models?

OPTIONAL HOMEWORK 6. Explain a phenomenon of evaporation that you did not try in this lesson using your group’s

consensus model of evaporation. Encourage students to practice this further.



Lesson 7

Construct an Initial Model of Condensation GET READY Objectives of the lesson

• To come up with their initial ideas about what happens to the surface of a cold object when a liquid appears on it and how and why that happens.

• To construct an initial model of condensation. • To become familiar with the modeling practice of ‘construct.’

IN CLASS OVERVIEW 1. In the solar still you observed at the beginning of this unit, liquid appeared in the bottle cap. To

understand how and why this liquid appeared, we will study this phenomenon more carefully in the next several lessons. In this lesson, you will begin to investigate this process by constructing an initial model of it.


CONDENSATION PHENOMENA 2. Look at the two pictures below and answer the following questions.

Figure 7. A cold Coke can Figure 8. A fogged up mirror in a bathroom

A. How are these two phenomena different? B. How are these two phenomena similar? C. Can you think of other phenomena that are similar to these two?

Have students look at Figure 7 and 8 and ask students what they notice.

Have students compare the two phenomena and individually write down their answers to each question.



Have students share their answers. You may want to record students’ responses on the board as they share their ideas and engage with these responses.

3. In all these phenomena, liquid appears on a cold object over time. This process is called condensation.

You could mention other phenomena of evaporation in addition to what students already mentioned such as: • Water (fog) appearing on eye glasses when coming inside on a cold day • Dew forming on grass • Rain water condensing from clouds • Water appearing on their cold lunchbox container

DRIVING QUESTIONS ABOUT CONDENSATION 4. Here are crucial questions we will focus on to understand condensation. Answer these questions

below. A. What changes did you observe over time? Where did the liquid come from? B. How and why do you think it happened? In other words, how and why did the liquid appear? C. How do you know?

Remember that these questions are basically the same questions that they saw before and about observation, explanation, and justification respectively (Note 1). Help students to note these emphases and individually write down their answer to each question.

CONSTRUCT AN INITIAL MODEL OF CONDENSATION 5. Construct your initial model of condensation in the box on the next page. It will help you think

about and understand condensation. You can choose any phenomenon of condensation for constructing your model.

You may want to review what model construction is about and why it is important (See Note 4).

Have students construct their initial scientific models of condensation in their SNs. Tell them to attempt to reflect their answers to the driving questions above in their models. • To help students construct their initial models, consider using some of the following instructional strategies:

○ Have students first create a picture or simulation in their heads of what they think happens to the liquid in their chosen phenomenon before having them draw their models on paper. This will help students see that creating an initial model is not just an exercise in creating artwork. This may also help them see that there is a difference between their idea model and their expressed model.

○ Have students think about what the main parts they should include in their model as well as the characteristics of and relationships among those components. You may also want to have students share their ideas about these components and record them on the board. Eliciting their ideas before having them express them on paper will help students produce models that reflect their complete initial understandings of the phenomenon.

○ One important feature that students should include in their initial models is the idea that the event takes place across time. Students can depict change over time, for example, by drawing a ‘before—during—after’ picture like in a comic strip or cartoon. (Note: Besides showing change over time, other aspects of a comic strip or cartoon are not particularly relevant for constructing models.)

○ Another important feature for students to include in their models is a ‘mechanism’ that explains what is happening to the water. Asking students to include this feature enables students to articulate their reasoning for how the water is changing over time rather than just having them provide a description of the change.



6. Explain your chosen phenomenon of condensation using your model in your group. Each group member should take a turn explaining his/her model to the others.

7. As a group, discuss what are similarities and differences among different models. While doing

this, you could also talk about some of the following questions. • Why did you choose that phenomenon for your model? • What are things you included in your model? What are things you didn’t include in your

model? Why did you do that? • How did you show how and why the phenomenon occurs in your model?

After students finish constructing their initial models, have them explain their chosen phenomena of condensation using their models in their group. Let them know that they need to answer the driving questions in their explanation.

As (or after) students share their initial models in their group, have them ask one another the questions suggested above in SN No. 8. Walk around and help each group to have a meaningful and productive discussion. While doing this, consider the four dimensions of scientific practices (Note 2).

[Optional] After the group discussion, you may want to lead a class discussion on the same questions in SN No. 8. Have each group share what they talked about and write down those ideas on the board. Compare and contrast different ideas and ask them relevant questions.

Conclude the lesson by announcing them that they will conduct investigations to gather evidence which will be used to

test their initial models of condensation.



Lesson 8

Empirical Investigations of Condensation

GET READY

Objectives of the lesson • To conduct a variety of empirical investigations in order to test their initial models about condensation. • To evaluate their initial models based on consistency with empirical evidence. • To develop their understanding of the modeling practice of ‘evaluate.’ • To develop their understanding of the evaluation criterion of ‘consistency with evidence.’


• Experiment 1: One cold ice pack, one electronic scale that measures to 0.01 grams, a clock • Experiment 2: One cold ice pack, one covered container (hood), one humidity detector, a clock • Experiment 3: One cold Coke can, one warm Coke can, one humidifier • For all experiments, a refrigerator/freezer or an ice box is needed to chill a Coke can and ice packs.

Teacher preparation • Set up stations for these experiments.

IN CLASS

OVERVIEW Just like you did when investigating evaporation, in this lesson you will do some experiments to test your model. If your model passes these tests (if it helps explain what happens and is ‘consistent’ with what happens), you could say your model is pretty good. If it doesn’t, you can get some ideas to make it better! BRAINSTORM EXPERIMENTS 1. To get some evidence to test our models of condensation, what kind of tests or experiments do we

need to do? As a class, think of some tests/experiments and talk about those ideas. Write them down below.

Summarize the main ideas from students’ initial models about condensation. • Here are some possible ideas that students may have reflected in their models:

○ The liquid came from inside of the bottle (i.e., water inside the bottle was leaking). ○ The liquid evaporated in the bottle. It escaped through a gap in the bottle (even though it is capped) and

condensed on it. ○ The liquid came from the clouds in the sky. ○ The liquid came from the air.

Help them to come up with ways (tests, experiments) to generate evidence specifically for their models of condensation.

By doing so, they could understand better the relationship between evidence and models (and explanations). Because this is challenging to them, you may need to give them more scaffolding and encouragement than correction.

EXPERIMENTS



Briefly review that they will PREDICT, SHARE their predictions with their group, OBSERVE, find a PATTERN, EVALUATE their models on the basis of evidence, and make a note of how to REVISE.

Before students conduct the experiments, explain what a scale does, how to measure weight using it, and how to determine weight. In particular, tell them that a number will keep changing when weight is measured (partly because of the error of the scale, movement of air, etc.) and that they need to choose the median value.

EXPERIMENT 1: WEIGHT OF AN ICE PACK 2. For condensation on the cold Coke can some may think that the liguid inside the can seep out

through the can. In the next three experiments, we will test this idea and determine where a liquid comes from in condensation. First, you will weigh an ice pack over time.

Figure 9. Weight of an ice pack

3. [PREDICT] Choose your prediction below about what you think is going to happen to the weight

of the ice pack over time. Also explain why you think so.

I predict that the weight of the ice pack will… because… Increase decrease stay the same Other:

______________________________________

____________________________________________________________________________________________________________________________________________________________________

4. [SHARE] Share your prediction and reason with your group. 5. [OBSERVE] Set the scale to zero. Take out an ice pack from the freezer and put it on the scale.

Measure the weight as described in the table below. Record all the weight measurements in the table below and write down any other observations you make. [Note: Because this scale is sensitive, follow your teacher’s instruction about how to use the scale.]

Measuring Point Weight (g) 1. As soon as you put the ice pack on the scale 2. After 20 seconds 3. After 40 seconds 4. After 1 minute



Other observations: 6. [PATTERN] What pattern do you see from your observations? Choose what you think is the

correct one. Over time, the weight of the ice pack

increased. decreased. stayed the same. Other: ______________________________________.

7. [EVALUATE] What does this result mean about where the liquid came from? How and why do

you think this happened? Evaluate your own model on the basis of this evidence. Can your model explain this evidence or not? Why or why not? Write down your evaluation in the table at the end of this lesson (Table 3).


Over all, this experiment is to test the idea that a liquid seeps out from the inside of a cold object as condensation takes place. Count how many students actually think this way. A sound prediction from this idea is that the total weight of the ice pack (the container of the ice pack + the content of the ice pack) will not change over time. To explain the actual result which is that the weight of the ice pack increased over time, this idea needs to be discarded and students need to recognize that the water came from the air.

EXPERIMENT 2: HUMIDITY IN A CONTAINER WITH AN ICE PACK 9. In this experiment you will measure the humidity over time inside a closed container in which a

cold ice pack is placed. Remember that humidity is a measure of the amount of water (or water gas) in the air.

Figure 10. Humidity around an ice pack

10. [PREDICT] Choose your prediction below about what you think is going to happen to the

humidity in the container when you place a cold ice pack in it. Also explain why you think so.

I predict that the humidity in the container will …

because…

increase decrease stay the same Other:

______________________________________

___________________________________________________________________________________________________________________________



______________________________________ _________________________________________ 11. [SHARE] Share your prediction and reason with your group.

12. [OBSERVE] Remove the ice pack from the freezer and wipe off the surface of it before putting it in

the covered container. Measure humidity in the container as described in the table below. Record all the humidity measurements in the table below and write down any other observations you make.

Measuring Point Humidity (%) 1. Before you put the ice pack in the container 2. As soon as you place the cup in the container 3. After 20 seconds 4. When humidity does not change any more

Other observations:

13. [PATTERN] What pattern do you see from your observations? Choose what you think is the

correct one. Over time, the humidity in the container increased.

decreased. stayed the same. Other: ______________________________________.

14. [EVALUATE] What does this result mean about where the liquid comes from? How and why do

you think this happened? Evaluate your own model on the basis of this evidence. Can your model explain this evidence or not? Why or why not? Write down your evaluation in Table 3.

15. [REVISE] While evaluating your model, what idea(s) did you have to make your model better?

Make a note of how to revise your model in Table 3. This experiment is also to test the idea that a liquid comes from the inside of an object. By observing that the humidity in

the air inside the covered container decreases over time, students will be convinced that a liquid (water) comes from the air or that water vapor in the air (gas) turns into water (liquid) on the surface of the ice pack.

EXPERIMENT 3: A COLD CAN AND A WARM CAN 16. In this experiment you will compare the extent of condensation on a cold Coke can and the extent

of condensation on a warm Coke can.

Figure 11. A cold can vs. a warm can



17. [PREDICT] Choose your prediction below about what you think is going to happen to the surface

of both cans when they are put in front of a humidifier. Also explain why you think so.

I predict that the surface of the cold can will have… more water than the surface of the warm

can less water than the surface of the warm

can the same amount of water as the surface of

the warm can Other:

______________________________________

because… ______________________________________________________________________________________________________________________________________________________________________________________________

18. [SHARE] Share your prediction and reason with your group. 19. [OBSERVE] Place both cans the same distance away from a humidifier and make observations of

the cans over time. Write down your observations below. • COLD can: • WARM can: • Other observations:

20. [PATTERN] What pattern do you see from your observations? Choose what you think is the correct one.

The surface of the cold can had more water than the surface of the warm can. less water than the surface of the warm can. the same amount of water as the surface of the warm can. Other:

___________________________________________________.

21. [EVALUATE] What does this result mean about how the water appeared? How and why do you think this happened? Evaluate your own model on the basis of this evidence. Can your model explain this evidence or not? Why or why not? Write down your evaluation in Table 3.


This experiment is to help students understand that the larger the temperature difference between an object and the air is, the better condensation takes place. Students will observe that more water droplets appear on the cold can than on the warm can over time. This empirical information will allow students to make their models more sophisticated.

To facilitate this experiment, you may want to place the two cans and a humidifier in a larger covered container.



Lesson 9

Scientific Ideas and Simulations of

Condensation GET READY Objectives of the lesson

• To explore scientific ideas and computer simulations of condensation. • To evaluate their initial models on the basis of existing scientific ideas and explanatory features of computer

simulations. • To develop their understanding of the modeling practice of ‘evaluate.’ • To be able to revise their models on the basis of various resources including evidence, scientific ideas, and

computer simulations. • To develop their understanding of the modeling practice of ‘revise.’


• Computer • Projector

Teacher Preparation • Check if the web sites for computer simulations work well. If your school blocks access to any of these sites, find

these files in “Multimedia Files” provided to you. Run all these links or files and think of what to talk about and what not to and other productive comments and questions.

IN CLASS OVERVIEW 1. In this lesson, your teacher will share some scientific ideas and computer simulations of

condensation. You can use these to improve your own model of condensation and to improve your own ideas about how this happens.

SCIENTIFIC IDEAS ABOUT CONDENSATION 2. Write down notes about the scientific ideas about condensation that your teacher shared with you. Here are some scientific ideas students need to know about condensation. Since students have heard most of them

from evaporation, review them by asking them reminding questions. • Conservation of matter: A general principle for most changes that occur in natural world is that matter does not

come into existence out of nothing and does not vanish. Simply put, matter is conserved through all changes although its form may change. (This is called the principle of conservation of matter.) To apply this principle to condensation, liquid does not appear out of nothing but gas turns into liquid during the process of condensation.

• The particle nature of matter: Matter is made of tiny bits or particles. Each tiny bit is too small to see with our eyes. So, when they are spread apart, we can’t see them. But, when they get together, we can see them. Each tiny bit also tends to move continuously. And as temperature increases, the speed of their movement also increases.

• States of matter: Matter exists in three phases (states): Solid, liquid, and gas. We can explain how they look different using the ideas we just learned about: tiny bits and their movement. When temperature is very low, tiny bits



of matter move very slowly to the point that they do not seem to move at all. They then come together, so we can see it as a substance with a shape. As temperature increases, the movement of tiny bits increases, so they get spread apart and the space between tiny bits become larger. Therefore, we can see liquid but it becomes fluid. As temperature increases further, the movement of tiny bits becomes so fast that they get spread very far apart. Therefore, this gas looks invisible.

• Condensation: In gas, tiny bits of matter move fast and so are spread apart. But as they approach a cold object, they become cold and their movement becomes slow to the point that they begin to clump or gather together. In the case of water vapor, the water becomes water drops through this process of condensation.

Invite students’ questions about any of these ideas and help them to understand them clearly. 3. Evaluate your own model in terms of these scientific ideas. Do you think your model includes

these scientific ideas? Why or why not? Write down your evaluation in the table at the end of this lesson (Table 4).


Follow the instruction in SN.

COMPUTER SIMULATIONS OF CONDENSATION 5. Explore some computer simulations your teacher will show from the websites below. You could

also check them out yourself later. • States of matter

○ http://phet.colorado.edu/en/simulation/states-of-matter ○ http://preparatorychemistry.com/KMT.htm ○ http://molo.concord.org/database/activities/201.html

• Changes of state ○ http://www.bbc.co.uk/schools/scienceclips/ages/9_10/changing_state.shtml ○ http://molo.concord.org/database/activities/180.html ○ http://www.footprints-science.co.uk/states.htm

6. Write down notes about what you learned from the computer simulations. It will be helpful to

consider the following questions. When zoomed in, A. What is matter made of? B. What does matter ‘look’ like in each state (solid, liquid, and gas), according to the

simulations? How do particles that make up matter move? C. How does taking away heat change what happens to a gas?

Before showing these simulations, have them read the questions in SN No. 6. Tell them that as they see simulations try to find answers to these questions. • Most of the answers were already addressed when scientific ideas were presented. But, as they see simulations,

they will find more concrete understandings about them.

Show them these simulations. As they see each simulation, ask some of the questions in SN No. 6 and engage with students’ responses. • Some of these websites contain too much information. So you need to decide what to show and to talk about.

As students explore the computer simuatlions, have them write down notes in their SNs about what they learned.



7. Evaluate your own model in terms of these computer simulations. Do you think your model includes features from these computer simulations? Why or why not? Write down your evaluation in Table 4.


Have them evaluate and revise their models on the basis of computer simulations as the did on the basis of the scientific ideas.

HOMEWORK: REVISE YOUR INITIAL MODEL OF CONDENSATION 9. Using the evaluations and revision notes you created in Table 3 and 4, revise your initial model of

condensation. Have students go back to Table 1 and 2 and see notes of how to revise their models. Some notes are recurrent. So,

have them summarize these revision notes and revise their models based on them.



Lesson 10

Evaluate Each Other’s Model of

Condensation GET READY Objectives of the lesson

• To develop the modeling practice of ‘evaluate’ in social environments IN CLASS OVERVIEW 1. In this lesson, your group and class will talk about what makes good models. Next, in your group,

you will share your model in your group to get others’ feedback. PEER EVALUATION 2. Go back to Lesson 5 to check the criteria you constructed for evaluating models and the way of

evaluating each other’s model. Use these in evaluating one another’s models of condensation.

3. When you share your model of condensation and the others give you feedback, write down that feedback according to each criterion in the table on the next page.

Have students revisit the class criteria for evaluating models listed on the class chart or in Lesson 5. • Before students revisit the criteria, you might want to ask them to talk about evaluating criteria to see how much

they became familiar with or internalized them. • Highlight again the criteria about the four dimensions of scientific practices (generality, audience/communication,

mechanism, and evidence).

Have them evaluate each other’s model of condensation in groups as in SN. • Because this is a second time they do this, they might be less interested than previously. You could motivate them,

for example, by saying, “When you guys did this the first time, you weren’t familiar with this. Now, you guys have experienced a lot of what scientists do by now, I believe you guys can do this much better than before and almost like real scientists.”



Lesson 11

Construct a Consensus Model of

Condensation

GET READY

Objectives of the lesson • To construct a consensus model of condensation. • To use the consensus model to explain and predict other phenomena of condensation. • To develop the modeling practice of ‘use.’

IN CLASS

OVERVIEW 1. In the previous lessons, you learned many things about condensation and modeling. In this lesson,

your group will construct a consensus model of condensation that reflects all of what you as a group have learned. Then, your group will try to explain other condensation phenomena using your group consensus model of condensation.

CONSTRUCT A CONSENSUS MODEL OF CONDENSATION 2. Using the class criteria for evaluating models, construct your group’s consensus model of

condensation on the next page. Review the class criteria for evaluating models.

Have each group talk about what parts from each member’s model to include in the consensus model and how to do it.

• Alternatively, you could facilitate a whole class discussion on this as follows. ○ Ask students which components they want to include in the consensus model. ○ Write them down on the board. ○ Point to some discrepancies among some components and lead a discussion to resolve them. ○ Ask students if they are related to the evaluation criteria. If there is any component that is not related to or

inconsistent with any evaluation criteria, lead a discussion to resolve it.

Have each group construct its consensus model of condensation.

USING THE MODEL TO EXPLAIN OTHER CONDENSATION PHENOMENA 3. As a class, make a list of other phenomena that might involve condensation. Each group will

explain one or two of them using its consensus model. Go back to Lesson 5 to check for suggestions for how to use your model. • Condensation phenomenon 1: _________________________ • Condensation phenomenon 2: _________________________

Together with students, make a list of other condensation phenomena. Assign them to the groups evenly. These

phenomena include:



• Water (fog) appearing on eye glasses when coming inside on a cold day • Dew forming on grass • Rain water condensing from clouds • Water appearing on their cold lunchbox container

Explain how to use a consensus model to explain other phenomena.

• If students have difficulty with understanding how to do this, you may need to do this for a condensation phenomenon.

Have each group use its consensus model to explain its assigned condensation phenomena. 4. Share how your group used your group’s consensus model of condensation to explain the

phenomenon. After each group finished using its model, have each group share how it did it with the rest of the class.

As students share their ideas, you might decide to further probe their thinking by asking follow-up questions that lead

them to make additional predictions about their situation. These follow-up questions might have them make predictions about what would happen under different conditions (e.g., colder/warmer weather, colder/warmer surfaces). For example, when having students explain why glasses fog up on a cold day, you might ask them to predict what would happen if it was a warm day and have them explain their reasoning. Or when having them explain how dew forms on grass, you might ask them to predict what would happen if it was a winter day versus a summer day.

After each group finished sharing how it used its model, you could ask students questions such as: • What are your compliments and wishes for how the other groups used their models? • What similarities did you notice among these ways of using models? • What differences did you notice across these ways of using models?

OPTIONAL HOMEWORK 5. Explain a phenomenon of condensation that you did not try explaining in this lesson using your

group’s consensus model of condensation. Encourage students to practice this further.



Lesson 12

Back to the Solar Still GET READY Objectives of the lesson

• To develop a model that explains what is happening in a solar still as it evaporates, condenses, and collects in a bottle cap and why.


• One solar still per group or class (You can reuse the ones from the beginning of the unit. However, you may need to make new ones if the water in the solar stills has been evaporating out of the containers rather than condensing in the bottle cap—this will have occurred if the solar stills had gaps in the container in which water could escape. To build new solar stills, follow the instruction in Lesson 1 of the unit.)

IN CLASS OVERVIEW 1. In this final lesson, you will go back to the solar still phenomenon and explain it by combining

your group’s consensus models of evaporation and condensation. COMBINE THE CONSENSUS MODELS OF EVAPORATION AND

CONDENSATION 2. As a group, look at your group’s consensus models of evaporation and condensation. Discuss (a)

what components to choose in each explanation and (b) how to combine them. Then make a decision as a group. • Components you chose from each model • How to combine them

Help students to relate the models of evaporation and condensation to what happens in a solar still by asking the following questions. • Which part of the solar still phenomenon do you think involves evaporation? Why? • Which part of the solar still phenomenon do you think involves condensation? Why? • Which part of the solar still phenomenon do you think might involves something other than evaporation and

condensation? (In other words, are there parts in the solar still phenomenon that can’t be explained by the models of evaporation and condensation?) Why?

Next, have each group discuss and make a decision on (a) and (b) in SN No. 2.

[Optional] Have each group share their discussion and decision on (a) and (b). When students share what their groups

talked about, ask them to give their rationale for their decisions. 3. Based on your group’s decision, construct your group’s model of the solar still phenomenon on

the next page. Have each group construct its model of the solar still phenomenon. Emphasize that they need to address the driving

questions we saw at the beginning. • What changes did you observe over time?



• How and why do you think these changes happened? • How do you know?

Have each group present its model of the solar still phenomenon (or explain the solar still phenomenon using its model) to the rest of the class.

4. Based on your group’s model, would you drink the liquid in the bottle cap? Why or why not? Have individual students write down their thoughts about these questions in their SNs.

• [Optional] Ask some of them to share their ideas with the class.

MORE IDEAS AND EXPERIMENTS OF THE SOLAR STILL PHENOMENON Share some scientific ideas about the solar still with students.

• Say, “Dirty water is made of up water and some other stuff like dirt. In other words, the dirty water is a mixture or solution. The bits of water from the liquid water are spreading out (evaporating) into the air and then clumping (condensing) around the plastic and sliding down the plastic into the cup. The reason why the still works is that only the bits of water evaporate and condense into the cup. The other parts of the dirty water will not evaporate at this temperature. So, the water molecules are the only ones that will fall into the cup – creating clean water to drink. So the final answer is yes, you could drink the water. This idea about the solar still is very important because many people around the world use the technique as a simple way to clean or purify dirty water. Clean water is extremely important for drinking and all kinds of other uses in our lives.”

• Say, “From your work with the solar still, you can also understand that the water that evaporates is the same as the water that condenses in the still. The water never disappears and no new water is made. This is called the conservation of water. For the most part, the water on Earth is also conserved. The water on Earth gets dirty and clean and changes from liquid to gas to solid to liquid, continuously through a water cycle. The water you drink and use everyday is the same water that has been around for millions of years.”

• You might connect this discussion to the water cycle in the sense that the same water just changes its form. If time allows, you might provide a detailed discussion of the water cycle.

Show students two short clips from Zoom videos about solar stills and discuss the ideas in them:

• Solar Still Part I: Salt Water ○ http://www.teachersdomain.org/resource/ess05.sci.ess.watcyc.solarstill1 - In this video segment, kids

assemble a solar still and make fresh water from saltwater, demonstrating two steps of the water cycle, evaporation and condensation.

• Solar Still Part II: Juice ○ http://www.teachersdomain.org/resource/ess05.sci.ess.watcyc.solarstill2 - In this video segment, kids test their

solar still to see if they can make fresh water from orange juice and blue sugar water.

OPTIONAL HOMEWORK 5. We have learned that scientific models are powerful tools for studying natural phenomena.

Choose any phenomenon that intrigues you and try to explain it by constructing a model of it. Encourage students to use this newly learned practice – scientific modeling – in their everyday lives.

6. Design an improved solar still. Use your own ideas and/or ideas you find on the web. Figure out

what parts or features can make it more or less effective. Be prepared to bring it in to the class and be ready to discuss what makes your solar still different or better.

You could use this optional homework as part of assessment if you want.

Documents

Evaporation & Condensation in a Solar Stillschwarz.wiki.educ.msu.edu/file/view/EvapCondTeacher Guide2011.pdf... · Rubber band Water Food coloring ... Imagine that you are lost in