The Why Behind Teaching This:
By conducting an experiment that requires students to identify and control variables, we are covering standard 3-5-ETS1-3: Plan and carry out fair tests which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved. The experiment is also providing students with some background knowledge on chemical changes which will be taught later in the year through standard 5-PS1-4 and 5-PS1-2. Although understanding the chemical change that is occurring in the experiment is not the focus, we do discuss it and it will provide a reference to reflect back on when these standards come up later in the year.
The goal of today's lesson is for students to work through the scientific process of experimenting by following the steps of the scientific method. Part of this process is to identify the variables that are being controlled in the experiment.
Students will demonstrate mastery of this by collecting accurate data throughout the experiment, and by analyzing that data at the end to share with others.
Preparing for Lesson:
I begin the lesson today by asking students to explain the Alka Seltzer experiment that they just completed Friday. What happened and why did it happen? Students explain that when they added the Alka Seltzer to the film canister of water, that the chemicals in the Alka Seltzer reacted with the water and a gas was produced. The gas built up in the film canister until the pressure caused the lid to shoot off. I use this as a teachable moment to review the concept of chemical reactions pointing out that the gas was a new substance created by the reaction between the Alka Seltzer which is a solid, and the water which is a liquid.
Show the Steve Spangler Mentos Gyser video. Pause it at 1.25 minutes after asking “Is it better for regular or diet?” Tell students that we will be testing another chemical reaction today, one between Mentos and soda. We will try to answer the question that was just posed by Steve Spangler, “Does diet soda or regular soda react the most with Mentos?”
Creating the Foldable:
I pass out a Experiment - Mentos and soda foldable for students to glue into their notebooks. I typed the data chart into this foldable because it is a large chart that will take some students a long time to draw. I have the same foldable glued into my notebook and have it projected on the overhead for students to use as an example. This helps the ESE and ELL students who need that visual for spelling.
We begin labeling the foldable with the question on the inside, upper left hand corner. While students are recording the question. I pass out the Experiment steps for Mentos and soda experiment to those students who struggle with copying, and I pass out the Procedure for Mentos and soda experiment to all other students. I provide all students the procedure because it is quite lengthy and takes too long to write it all down.
I ask students what step of the scientific method follows the question and they are able to tell me the hypothesis. We record the hypothesis as an if/then statement in our foldable and I ask students to fill in the blank with their hypothesis.
We continue to go over the experiment by going through the materials and procedure. I record the materials for students to copy, and we all paste the procedure into the foldable. While going over the steps of the experiment, I am acting out what students will be doing and we are discussing what variables must be kept the same. This will help when we record our variables before beginning the experiment.
After we go over the procedure, we draw a data chart in the center of the foldable divided into 4 columns, and 11 rows. This will be used for recording data for the experiment. As we are creating the data chart, I point out that there are five types of soda, a regular and a diet for each type. I chose five because I have five groups in my class so each group will test one of the types of soda. I have done this with cans of soda and purchased enough for each group to test their own can of each but it gets expensive, and the explosion from a can is not as impressive as that from a 2 liter. The columns are to record the beginning volume (should be the same for all), the volume after the reaction, and the amount that exploded.
If you would like a more close up view of the data chart in the foldable you can see it here: Foldable Picture
Before going outside to start the experiment, we identify the variables for our experiment. Students are able to tell me that the independent variable is the diet soda and regular soda. They are able to tell me the dependent variable is the size of the reaction that occurs. I have to make it clear that the way we are measuring this reaction is by measuring the amount of soda that explodes out of the bottle. I have them explain to me how we are going to figure out how much came out of the bottle if it is all over the ground. This allows me to review and check for understanding on what the measurements in the data chart mean. Students identify the control variables as the size of bottle, the amount of Mentos, the type of Mentos, the time we open the bottles, and the place we are testing. I am pleased that they are able to identify so many, because this was the variable they have had the most trouble with.
Conducting the Experiment:
I hand each group their two bottles of soda and remind them that one control variable they did not mention was not shaking the soda. I tell the students carrying the bottles to be careful not to shake them while taking them outside.
We all sit outside and the group with the Coke goes first. To make it fair for all group members (there are 4 in each group), I tell 2 students to open the lids, and the other 2 students to drop in the Mentos. All four students help measure. I let them set their soda aside and measure at the end so that they can watch the other sodas explode. All groups measure at the same time at the end.
Groups continue testing and the rest of the class observes as the sodas explode out of the bottle. In the first Video of students testing you can see that I placed a piece of cardboard under the bottles. This helps make sure the bottles are leveled and prevents them from tipping over when they begin to explode. This video shows how the students follow the procedure perfectly by unscrewing the lids at the same time, and then dropping the Mentos in as the other students count.
I chose the second Video of students testing because it shows the excitement in students as they watch this experiment take place. You can hear the students excitement as they cheer and one student in the background even yells "I love this!" As a teacher, it is always nice to hear and see your students get excited over your lessons. It makes the planning and money spent well worth it.
The Video of students measuring shows one group measuring the amount of soda left in the bottle so they can determine how much exploded out. They use both measuring cups because there is too much soda left to poor into one. If you do not have a large measuring cup, or more than one to provide each group, just remind them to record what they have before pouring it out and adding to the total.
Sharing Data and Drawing Conclusions:
Groups measure the amount of soda left in the bottle and then we share the data so everyone can fill in their data charts. We analyze the data together by comparing each type of soda separately. I ask the students which reacted the most, the Coke or Diet Coke, they tell me the Diet Coke. We move on to the Sprite and Diet Sprite and they tell me the Diet Sprite reacted the most. After going through each soda individually, we determine that in every situation, the diet soda reacted more than the regular soda. Students use this information to write their conclusion. I remind them that they need to refer back to their hypothesis, determine if their hypothesis was correct or incorrect, and what evidence made them come to that conclusion.
Students complete the bar graph for homework and we share a few of those the following day.