MnSTEP Teaching Activity Collection > MnSTEP Activities > Sorting Our Way to pH

Sorting Our Way to pH

Joan McKinnon
Lincoln Elementary School
Bemidji, MN
Loosely based on lesson from NSTA Press, "Picture Perfect Science Lessons," and Red Cabbage Juice Activity
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In this indoor lab activity students will be given a large variety of objects to sort into categories. After practice and discussion, they will then sort food items; first based on their five senses, then by studying their reactions when placed in red cabbage juice. Students document their predictions, observations, the results of their work and their conclusions.

Learning Goals

Students will investigate the concept of sorting objects. This concept connects to a deeper concept that sorting isn't always based on visual aspects of an object. Rather, the chemical makeup of an object can determine characteristics as well. Throughout the investigation, students will receive practice of recording their predictions, observations and their conclusions. Learning to form a hypothesis will also be a valuable aspect.

Context for Use

Grades 4-6
Class size 30
Elementary classroom lab experience
Approximately 2-3 days to complete lesson

Subject: Chemistry:General Chemistry:Acids & Bases,
Resource Type: ActivitiesLab Activity
Grade Level: Intermediate (3-5)

Description and Teaching Materials

Equipment needed:
1. Any type of collection: shells, button, marbles
2. A variety of food items, such as: vinegar, water, corn starch, lemon juice or lemons, flour, baking soda, pickles,
soda pop, baking chocolate.
3. Juice cooked out of a red cabbage.
4. 5 or so test tubes for each group of students.
5. Strips of litmus paper (optional.)

On day 1 students are given a number of objects from a collection; buttons, shells, etc. They are then instructed to sort the objects into two groups, then to divide each of those groups into two more. Continuing in this manner until they have a group containing only one object. Students should be recording every step of the way, the manner in which they are creating each of their classifications.
The teacher is observing, questioning and noting the conversations that are taking place among the students. A discussion follows regarding the uses of classifying objects in our everyday world. A library, card shop, color crayon box, etc. are practical examples where classifying is extremely helpful. Students may even be assigned to find other places where they see an example of classifying.
On day 2, students are shown the food items from the materials list (vinegar, lemons, flour, etc.) and are given the task of placing these items into categories as they did in the preliminary sorting activity on day 1. The students are again recording their observations and findings in their notebooks and the teacher is questioning and observing students in their groups. Once students have been given ample time to sort the food items, another discussion of their findings should follow. The teacher then introduces the scientific notion that when substances are mixed together, sometimes a reaction takes place. (Possibly day 3) The students will be placing some red cabbage juice in each of their test tubes and then will add a small portion of one food item (somewhat liquefied with distilled water) in each test tube. The students will again record their actions, observations and their conclusions. They will again be instructed to sort the foods based on their reactions with the red cabbage juice. The teacher will again create discussion where the students present their conclusions and the results of their final sorting. At this time the concept of pH can very basically be presented. If the teacher chooses, students can continue on to a more in-depth study of pH.


The concept of classifying objects and recording work are really the main concepts of this lesson. Introducing the pH concept needs to be very basic at this level. Therefore, given several opportunities to observe students sorting and recording their individual data provides plenty of opportunity for the teacher to evaluate students individually through observation and questioning.


A. Scientific World View
2. Recognize that clear communication of methods, findings, and critical review is an essential part of doing science.

References and Resources