Boiling and Freezing Points Lesson 2: Oh Boil, the Pressure!
Lesson 11 of 12
Objective: The students will be able to explain how solutes and pressure affect the boiling/freezing points of liquids. The students will also be able to describe the energy transfer that occurs during phase changes.
This lesson, "Oh Boil, the Pressure!", is the second of a 3 lesson series. If all aspects of this lab rotation are completed, this series of lessons will take 4 to 5 days to complete.
This lab rotation consists of three very exciting labs that students love! These stations focus on how solutes and pressure can affect the physical properties of the substances involved. However, for me, this set of lessons serves a larger purpose. It is designed as a summative assessment for some scientific literacy pieces that my students have been working on: reading, writing, and group discourse/discussion. Each station, including the reading, writing, and discussion takes about one and a half to two class periods. On the Better Lesson website, each station of this rotation is a separate lesson. The stations/lessons include:
On Day 1: All Hail the Freezing Point, students "flash freeze" a test tube of water! Students drop a small piece of ice into a super-cooled water test tube and the entire test tube freezes instantaneously!
On Day 2 (this lesson): Oh, Boil the Pressure!, students make water freeze at 50 degrees Celsius!
On Day 3: Blow it Up with Butane, students feel a liquid that is boiling that is cold and makes cool popping sounds!
For each of the lab stations, students must read for information independently and track what they are thinking as they read using reading strategies of "Talking to the Text" and the "Ladder of Discourse". Then, students follow a procedure to complete a lab station featuring an unexplained phenomena. Next, students write a well developed scientific paragraph using a format we call "ABCDE" in which they must cite multiple sources of evidence while they maintain a formal tone. Finally, students partake in group discourse and discussion as they verbally cite textual evidence and qualitative observations to support their ideas. It is truly a culminating event in which students must demonstrate mastery of both scientific content and literacy.
Now, you may be thinking, that is a lot! But, I will tell you, I truly believe this series of lessons is worth looking at. I am confident that whether you use each lesson in its entirety or not, each lesson has something you can use in your own classroom. This set of lessons includes reading and text strategies, scientific writing techniques, cool lab stations/demonstrations, and insight on how to promote deep discussion and discourse from your students. There is something for everyone!
Thus, please keep this in mind when you look at the next section that describes the connections to the NGSS and the Common Core and see the large bundle of standards that this is a set of 4 to 5 days and is a summative assessment of many reading and writing skills.
This series of lessons is designed to reach the following NGSS Standards:
MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MS-PS1-4 Develop a model that predicts and describes changes in particle motion, temperature, and state of a pure substance when thermal energy is added or removed.
In addition, these lessons connect to a number of literacy Common Core Standards.
Science and Engineering Practices:
When using the text strategies utilized in this lesson, students think deeply about text in order to make their own conclusions and consider solutions to problems. Thus, students are using the Science Practice of Generating Questions and Designing Solutions which states that "Students at any grade level should be able to ask questions of each other about the texts they read, the features of the phenomena they observe, and the conclusions they draw from their models or scientific investigations. For engineering, they should ask questions to define the problem to be solved and to elicit ideas that lead to the constraints and specifications for its solution." (SP1)
In preparation for performing the lab stations, students use strategies to obtain scientific information and evidence from text (SP7). In addition, students back up their explanations in the lab document with evidence from their qualitative observations (SP8).
When students discuss what they see in the lab in comparison to what they read in the text, students can begin to see patterns how adding a solute can affect the properties of solvent. Thus, students can begin to see that macroscopic patterns are related to the nature of microscopic and atomic-level structure (Patterns). In addition, as a part of this lab, the students students track how energy is transferred within systems during phase changes (Energy and Matter).
Ask students, "What are you going to learn today?". Students should respond by saying that they will be answering the Essential Question, "How do particles combine into new stubstances? And, what evidence can show how the physical and chemical properties of the substances change?" This EQ is posted on my board and on the student's Chemistry Unit Plan.
Explain that today they are going to continue the series of lab stations that will allow them to demonstrate not only their understanding of physical properties and factors that influence them, but to show their mastery of reading for understanding, writing scientific explanations, and discussing in groups with group discourse techniques. Let students know that their content focus will be Skill 4 on their Chemistry Unit Plan which states "I can identify the physical and chemical properties of the reactants and products in a reaction." Specifically, students are going to pay close attention to physical property changes caused by pressure and how energy transfers as matter changes phase.
**It is important to note that my students have already been introduced to physical and chemical properties as well as endothermic and exothermic reactions before this lab. To see their introduction to these concepts, check out the following lessons: Crack that Marble Labs (chemical and physical properties) and Talk About Burning Your Money! (phase changes, energy transfer, endo- and exo- thermic reactions).
Remind students that they should thoroughly read all procedures before beginning this lab station. Emphasize that they are being assessed on their ability to "Talk to the Text" and reach the top rung of the "Ladder of Discourse". Thus, taking time to thoroughly complete step one of the procedure is essential. Explain to students that pulling the stopper out of the syringe will be challenging, students will need to use their muscles! And show students the grip they should have on the syringe. If students hold the syringe in a manner that will cover up the water, they will not be able to see the reaction occurring. Watch the video following the procedure to look at the student's grip on the syringe. Once students have completed this procedure, they should begin answering the question from the lab document.
- Read the “Oh Boil, the Pressure” background knowledge before you begin.
- Wearing goggles, fill a beaker with 100 ml of water.
- Place the beaker above a Bunsen burner with a thermometer in it.
- When the beaker reaches 60 degrees Celsius, use tongs to remove the beaker from the heat.
- Fill the syringe about half full of the 60 degree water. Put the cap on the syringe. Hold the syringe pointed down and prepare to pull up on the plunger. Make sure your hands are not covering the base of the syringe so that your group can watch what happens inside. Observe what occurs inside. Record what temperature water boils at below sea level pressure.
When trying to understand why this occurs, students often can pull from the text that the pressure inside the syringe must be decreasing. However, they have a hard time understanding why it is decreasing. Often students say, "But when I pull out the stopper, it is hard. Doesn't that mean higher pressure?" For struggling students I often draw this diagram:
By assigning an arbitrary number of gas molecules that were originally in the syringe and explaining that because of the clay, no new gas molecules entered, students can realize that the gas had to spread out to fill the new space created by pulling up the stopper. Thus, the pressure decreases.
Question 3: If you wanted to cook your pasta faster, which method would you use -- add a solute or lower the pressure? Why?
Once students have completed their ABCDE paragraphs, have students conclude the lesson by peer editing their responses. When peer editing, I use a process I call, "Put Your Finger On It". I provide the students with a checklist of items they should be able find in their peer's writing (Checklist is included in resources). For each item, they have to physically touch it with their finger. If they cannot physically touch it, they provide their peer with feedback about what they are missing so that student can make corrections.
It is important to emphasize and follow through that the students are actually touching the paper with their fingers. In my experience, students just check things off the list. As students peer edit, I ask them to show me where they actually found items on the list. Physically touching the paper to find the important items increases the student feedback.
Allow students to have time to make the revisions necessary based on their peer's feedback.
This video takes a look into student work at every rung of the "Ladder of Discourse". It goes through "talking to the text" for every station in this lab rotation.
This video shows and explains ABCDE Paragraph and Multiple Citations Strategies, using student work from Oh Boil, the Pressure!