In this lesson, students go through a series of lab stations in order to practice identifying reactions as chemical or physical changes and determining the physical and chemical properties that change during the reaction. At each lab station, students not only identify the signs of a chemical change, but they also read reactant and product descriptions in order to identify changes in chemical and physical properties that occurred. Each station is fun and allows students to get a real visualization of evidence that can predict a chemical change!
This lesson is designed to connect to the following NGSS and Common Core 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.
CCSS.ELA-LITERACY.RST.6-8.1 Cite specific textual evidence to support analysis of science and technical texts.
CCSS.ELA-LITERACY.RST.6-8.3 Follow precisely a multistep procedure when carrying out experiments, taking measurements, or performing technical tasks.
CCSS.ELA-LITERACY.WHST.6-8.1.B Support claim(s) with logical reasoning and relevant, accurate data and evidence that demonstrate an understanding of the topic or text, using credible sources.
CCSS.ELA-LITERACY.WHST.6-8.9 Draw evidence from informational texts to support analysis, reflection, and research.
Science and Engineering Practices:
The NGSS asks that students develop and/or use a model to predict and/or describe phenomena (SP2). In doing this, students should construct, use, and/or present an oral and written argument (SP7) supported by empirical evidence and scientific reasoning to support or refute an explanation or a model for a phenomenon. When students look for patterns in data to identify the signs of a chemical change based on their qualitative observations, they do just that! Therefore, this also means that students analyze and interpret data to provide evidence to describe phenomena. (SP4)
At each lab station, students use patterns in evidence to identify each reaction as chemical or physical. Students thus realize that patterns can be used to predict phenomena. In addition, students look at chemical equations and start to make clearer connections to the idea that bonds are broken and formed during chemical reactions. Thus, they can realize that macroscopic patterns are related to the nature of microscopic and atomic-level structure. (Patterns)
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 substances? 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 to students that we will again be working with Skill 5 of the Chemistry Unit Plan, "I can provide evidence to show if a reaction is a chemical or physical change." (At this point, my students have already been introduced to the concepts involved in identifying reactions as chemical or physical in previous lessons.) Have the students turn to their unit plans and silently read the skill. After reading the skill have the students rank their current level of mastery on a scale of 1 to 4 (4 being mastery). Students in my room have already assessed themselves in the lesson prior to this; this would be an opportunity for the student to change their number if they felt their level of mastery had increased after the previous lesson.
In my classroom, students frequently self-assess their level of understanding on each skill in the unit as we go. As you can see from the image below, this student ranks has continually updated his level of mastery on each skill has his learning has developed.
Students in my class have already had an introduction to the differences between chemical and physical reactions. The Skill 5 Notes Page along with a True/False Statement Worksheet is included in the resource section that my students have already worked through when they complete these labs.
For a look at all the lessons that have led my students to this point and where we go from here check out the lessons in these units:
Physical Properties: Molecular Arrangement and Phase Changes: Focuses on Skills 1 - 4 of the Chemistry Unit Plan
This unit is designed to answer the Essential Question, "How do particles combine into new substances? What evidence can show how the physical and chemical properties of the substances change?". It particularly focuses on types of matter, physical properties, phase changes, and factors that affect physical properties. This unit's purpose is so much more than just the content, however. It's focus is scientific literacy. It stresses group discussion, discourse and utilizing text references when engaging in argument. Students utilize reading, writing, and speaking strategies in order to develop scientific literacy. It's scientific literacy immersion!
Chemical Properties and Reactions: Focuses on Skills 4 - 6 of the Chemistry Unit Plan.
This unit is also designed to answer the Essential Question, "How do particles combine into new substances? What evidence can show how the physical and chemical properties of the substances change?". This unit focuses on chemical properties and chemical reactions. Students analyze evidence and property changes that allow them to distinguish between chemical and physical reactions. In addition, students investigate the Law of Conservation of Mass as they look at how bonds are broken and formed in chemical reactions. This unit is full of hands on labs and station rotations that will engage any middle school student in chemistry!
In previous lessons, students have been looking for our "five signs of a chemical change" (color change, gas production, solid formation, temperature change, and pH change) as well as analyzing physical and chemical properties that change during reactions. Students have already read and gone through one lab series relating to these topics. This lab rotation represents the students second lab experience and thus, I am asking them to back up all claims with multiple pieces of evidence as we increase the complexity of our understanding with each lab station.
My conversation prior to these lab station unfolds something like this:
Teacher: "Scientists back up their claims with qualitative and quantitative data as well as with evidence found from credible text resources. The more evidence they can find to support the claim, the stronger their argument will be. Thus, in the lab rotation today, you must "channel their inner scientist" and do the same! At each lab station you must determine if the reaction observed is a chemical or physical reaction. In addition, you must cite properties that change as a result of the reaction.
When making these claims, it will be important that you cite qualitative as well as quantitative data. (We use these words frequently, but a quick refresher of these words could be in order!) For example, pretend a student watched a reaction in a zip lock bag. The bag bubbled, got cold, and turned from blue to red. Thus, the student determined that it was a chemical reaction. Then, they responded to the first question of the lab station. Take a look at your lab document - notice that the questions are similar for each station. One of the questions for each station is "Did you just observe a chemical or physical change? What evidence do you have to prove this? Back up your evidence with observations!". Let's pretend the student writes the "Chemical. Color change. Bubbles. Temperature change.". What feedback would you provide the student with in terms of "sounding like a scientist and not like a 7th grader?"
Write the response on the board and make corrections as students provide feedback. Students should say things such as "Write in complete sentences.", "Explain what colors they saw.", "Explain what temperature change they observed.", and "State that the bubbles mean gas production.".
When complete, the response might read, "This is a chemical reaction. There was gas production when the bubbles formed. The color changed from blue to red. In addition, the temperature changed when the bag decreased in temperature."
Teacher: "Next, the student begins to answer the question that asks, "What are some properties of the materials involved that changed? Describe." Notice that along with your lab document you received a page that describes the properties of the reactants and products for all of the reactions. Scientists also cite evidence from text to support your claim. Thus, when answering this question, the student could reference the data included in this page to support their claim. Remember, when citing data, it is important to compare data points to demonstrate the change that occurred. Take a look at the property description for the Pop Your Top Lab Station. It states:
Reactants: Alka Seltzer is a white solid that breaks apart easily. It is made of sodium bicarbonate which is ionically bonded and reacts when in the presence of an acid. Water is a liquid and has a boiling point of 100 degrees Celcius.
Products: The product of this reaction is carbon dioxide which is a colorless gas that has a boiling point of -56 degrees Celsius. Carbon dioxide does not react strongly with acids.
If I was going to note that the boiling point changed, as a scientist, I would not simply write "The boiling point changed." Instead, I would back it up with data from the text. I might write, "The boiling point of the reactant was 100 degrees Celsius while the boiling point of the product was -56 degrees Celsius." Comparing two data points strengthens my claim. Last, when noting the changes in the properties from the reactants to the products, please be sure to note at least one physical property that changed and one chemical property that changed."
Split students into groups. There are five stations. I tend to put enough materials at each station so that two groups can be at a station at a time working next to each other. In other words, I split my classes into 10 groups. I remind students that they must wear goggles at all of the lab stations and that as scientists, reading and following procedures is not only important to the success of the lab, but to their safety as well. In addition, I explain that groups must complete all lab questions first before rotating to the next station. (This is important - middle school students will just want to do all of the "fun" very quickly and will try to save all of the "work" for the end. This is simply not effective for their learning. All questions for the previous station must be completed prior to rotating to the next station!)
Setup and Materials:
Notice that the student stated both that bubbles formed and that that was an indication of gas production. So, she not only stated the "sign of a chemical change", but she backed it up with a qualitative observation from the lab. In addition, notice in the properties question, the student compares data she found from the text of the reactants to the products in order to provide evidence of the change.
Setup and Materials:
The student above recognizes that this is a chemical reaction. She not only cites one piece of evidence as gas production, but she supports that evidence with a qualitative observation (bubbles). In addition, she notes that the color changed from silver to brown, which again utilizes a qualitative observation from the lab.
The student above is able to identify that the products are located to the right of the arrow in a chemical reaction and that the reactants are located to the left of the arrow. In addition, she does a nice job comparing the properties of the reactants to the products and cites one chemical property (reactivity with acid) and one physical property (color) that changed. Notice that she did not simply state, "The color and reactivity with acids changed.". She describes the property before and after the reaction.
Setup and Materials:
The student above demonstrates both mastery and misconceptions. In the first question, she is able to recognize all three signs of a chemical change (color, gas production, and temperature change) that can be observed in this reaction and she backs each of those up with an observation from the lab (ex. the temperature changed from room temperature to hot).
The second question however, this student has some misconceptions. Because she noticed the tin foil was hot, she stated that it was gaining energy and thus was endothermic. Students often have a difficult time understanding this energy transfer. Instead, the student should have noted that the tin foil was releasing energy (transferring energy to its surroundings) making the reaction exothermic. Students that struggle with this concept focus on words like "hot" and "cold" rather than considering the energy transfer that is occurring from the reaction to the surroundings.
In the third question, this student was able to compare properties between the reactants and products; however, she listed two physical properties rather than identifying one chemical and one physical property. If not required to include physical properties, students will focus on physical properties because that is what they are most comfortable with. It is important that students practice using and analyzing chemical properties as well.
Setup and Materials:
Initially, oxygen bubbles are produced.
These white bubbles can be used as fuel to ignite the red embers at the end of a wooden skewer.
In the first question, this student demonstrates some of the challenges that many students have in this lab. For example, the student notes that there were bubbles formed, but does not indicate that this is a sign of gas production. Then, the student mentions that there was a temperature change but does not back it up with an observation from the lab or indicate that the temperature increased. Moreover, the student did not even include that there was a color change when the skewer turned from brown to black. Not including all pieces of evidence and not backing up their evidence with qualitative observations from the lab is the most common problem students have in this question type.
In the following questions, the student does a nice job citing both a chemical and physical property and how it changed after the reaction. In addition, the student is able to identify that the reactants are located to the right of the arrow in a chemical reaction and that the products are to the right of the arrow. This question can actually cause students to second guess themselves. At this point, it may be their first time seeing a decomposition reaction. Some students have the misconception that in a reaction there has to be more than one reactant that combines to form one or more than one product.
Set Up and Materials:
To close, I have students complete this exit slip. The purpose of this exit slip is more than identifying the signs of a chemical change; it is in identifying physical and chemical properties that change as a result of chemical and physical reactions.
After students complete this "exit slip", I sort the formative assessments into piles of similar learners. Then, in an upcoming lesson, I can conference with these groups. The groups that I typically need to meet with include:
1. In Question #1, many students do not really analyze the properties that are changing during phase changes. When I meet with this group, I have them discuss what is occurring to the energy and molecules as water freezes or evaporates and then they can come to the correct conclusion. For most, if they miss this question they either need to learn to slow down and think about what is actually occurring in reactions or they have a misconception about what boiling point actually means.
2. In Question #2, some students show that they are still having the misconception that phase changes and dissolving are physical changes and that when a new color appears, that would indicate a chemical change.
3. In Question #3, students confuse the color change that results from food coloring as a "color change" and thus need to be taught that food coloring dissolving in water is a physical change and that a new color has not been produced. The water simply turned green because the food coloring was green.
4. In Questions #4 and #5, students need to be able to recognize that in physical reactions only physical properties change and that in chemical reactions chemical and physical properties can change. Some students have the misconception that in physical reactions no properties change. In addition, students need to have a familiarity with different properties in order to name them.
After meeting with these conference groups, I have students chart their growth on formative assessments on their "Working Towards Mastery List". After plotting their point, the students list the things that they are still working on.
A great example of this can be shown in the students work below. By creating a "Working Towards Mastery List", students develop their own individualized plan for growth!