Prior to teaching this lesson, you will need to make the cabbage juice indicator. There are a couple of different ways this can be done. I purchase one red cabbage and chop it up. I boil one cup of cabbage in two cups of water for about ten minutes or until the water turns purple. Just a warning, this will generate a particular odor. Also, the cabbage juice will last a couple of days if it is refrigerated, but it will begin to smell badly. One cabbage will produce about two gallons of cabbage juice, which can be diluted if necessary. As for the household liquids, I generally purchase a variety of clear generic liquids for the students to test. This is also an excellent time to use those hotel shampoos and conditioners you have been collecting because you are a science teacher and "might need them for something in class."
I also use Vernier LabQuests and pH probes for this lab as well as litmus paper. This helps students see that there are a variety of ways to collect scientific data.
When the students enter the room, they take out their journals and begin writing about the prompt, What is pH? How do you know? As the students write, I circulate through the room reading through their answers. Once everyone has had an opportunity to write down information, I ask for volunteers to share their answers with the class. The students are able to identify that the pH scale is a range of numbers that represent acids and bases. They are able to use some of the terminology from the notes, but most do not have a deep understanding of the topic.
I ask the students to take out the copies of their flipped notes, so they can refer to them as we review the information in class. This is the flipped notes video that I created specifically for my students.
I am careful to point out that the pH scale is logarithmic. This is not something that I test the students on, but it is important to understand the magnitude of the change represented by each number on the scale and it also helps to address NGSS SP5.
After reviewing the flipped notes with the students, we review the pH lab sheet. The lab will be divided into two separate days, so the students will need to have their pH predictions made in order to participate in the lab the next day.
I place the students into groups of four and they pick up their Chromebooks on the way into the lab. While in the lab, the students open their lab sheets on their Chromebooks and begin reading through the information.
The students are able to examine the liquids on the supply table in order to fill out their charts. As the students work on their prediction charts, I circulate through the room asking the students questions and encouraging them to refer back to the acid/base characteristics written in their notes in order to justify their predictions.
This video of student predictions provides an example of our discussions. Once students have made and justified their predictions, they are able to begin working on the lab. Some groups are able to begin testing items on the first day, but others are not.
Working on the laboratory exercise helps to meet NGSS MS-PS1-2 as students are identifying the results of an chemical reaction to determine whether a substance is acidic or basic. Additionally, the conclusion of the lab meets NGSS SP4 and SP8 as students are required to conduct an investigation to determine pH and then use data to support their findings.
When there are five minutes left of class, I lead a whole group discussion about the liquids the students decided to test and what they think their results will be. Basically, I ask them to explain the information they included on their prediction chart. At this time, I am careful to ask students to justify their predictions and ask them to use the terminology we discussed in class while reviewing their flipped notes.