You are what you eat: pH in Food
Biology In Elementary Schools is a Saint Michael's College student project from a course that ran between 2007 and 2010 and fully described in this book chapter. The student-created resources have been preserved here for posterity. Link under 'toolbox' for printer-friendly versions of the exercises. Click on handouts to print full resolution versions. Please see Wikieducator's disclaimer, our safety statement, and the Creative Commons licensing in English and in legalese.
Tried and Trusted
Primary biological content area covered
- We will have students become aware of what pH is, why one should be aware of pH, and which foods have lower or higher pH.
- We will help the students learn the effect that acidity can have on their cells and their entire bodies.
- We want the students to understand that the pH level in food eaten daily has effects on their body.
- 50 pH strips, refer to 1a for photograph
- 4-350 mL mason jars or beakers
- 2 Laminated enlarged color pH scales, refer to figure 8 for photograph
- Handouts ' You are what you eat: pH in food!' 
- White bread (bagel, refer to figures 2 and 3 for photographs
- American cheese, refer to figure 4 for photograph
- Orange, refer to figure 5 for photograph
- Lemon, refer to figure 6 for photograph
- Apple juice, refer to figure 7 for photograph
Description of activity
First we will explain pH scale to students. pH is a scale that measures how acid, or basic (alkaline) a substance is. The scale ranges from 0 to 14 with 0 being the most acidic a substance can be and 14 being the most alkaline, 7 is the number for a neutral substance. We will have students test foods and drinks that they encounter in their everyday lives to see where they fall on the pH scale. To finish up the lesson we will have students discuss and think about how eating foods that fall on either side of the scale effects their bodies and health.
 Introduction to Topic Introduce the students to the scientific vocabulary that will be used in the lesson. Explain to students what they will be doing throughout the experiment.
 Handout Give students the handout, and without any scaffolding, have students answer question 1. Once students are finished with the first question, we will define what pH is and where it is most commonly found. Next have the students answer the second question, have students share their responses to the rest of the group, and discuss why they chose those foods.
 pH strips Before the students test the food with the pH strips, it is imperative for teachers to explain how to use and read the strips. This is to avoid any unnecessary confusion and complication. We will demonstrate how to test and read a pH strip, to make sure the students understand.
 Testing the food Each student will be give on item of food that they will be responsible for testing. Every student will receive the item of food, 150 mL of water (neutral), a jar or beaker, the pH strip, and an enlarged pH scale.
Bread, Turkey and Cheese: Have students rip the piece of bread, turkey and cheese into small sections. Put the small pieces into the jar or beaker. Add the 150 mL of water directly on top of the bread, turkey and cheese, allow the water to absorb into the bread, turkey and cheese for approximately 45-60 seconds. Have students take the pH strips and put it directly into the jar, making sure the strip is covered in the water. (refer to figure 2 3 and 4 for photograph)
Apple Juice Have students measure 150 mL of apple juice. They will pour the measurement of apple juice into a jar or beaker. Next have students take the pH strips, and place it into the jar or beaker, making sure that it submerged in the apple juice. (refer to figure 7 for photograph)
Lemon and Orange Prior to having students test the lemon, we will cut a small incision into the lemon. This will be deep enough that the pH strip will be completely submerged. Students will place the pH strip into the cut and wait for the results.(refer to figure 5 and 6 for photograph)
- When placing the pH strip in either the jar or food directly, allow approximately 5-10 minutes for the pH strip to correctly test.
Analyzing the Data
- Once the pH strips have been submerged in the food content for the appropriate time, the students will match the pH strip to the enlarged color pH scale. Having the enlarged pH color scale, will help the students be able to clearly identify the pH level. They will easily be able to compare the colors on the pH strip to the enlarged color pH scale. (for the enlarged pH scale please refer to figure 8 for photograph)
- Once the students have identified the level of pH on the enlarged color pH scale, they will record the data on the graph that is found on their handout.
 Making Predictions
- Once the students have completed testing their food, and analyzing the data, we will have the students refer back to their handout. We will have the students look back to the first question, and see what their responses were. This was when the students wrote a hypothesis,hat is pH? And where is it most commonly found? We will have the students tell us what the have now learned about pH after testing the food.
 Health Connections
- We will have students complete the last question on the handout, prior to having the students discuss what they think the different pH levels will do to their health.
- Once this is completed, we will discuss the affects of pH on their health.
- As an example, we will talk a piece of chalk and pour a high concentrated amount of vinegar. This will show the students the affect that a large amount of acid has on their body, and we will discuss the implications of this on their stomachs and teeth. We will explain to the student's that eating large amounts of acidic foods, will ultimately wear away at the enamel of their teeth.
- We will discuss to the students, to eat their foods in moderation. Since the majority of the food that they eat will have low or high pH levels, we want them to be aware of pH in their foods, and a healthy eating style.
- Alkaline- A substance that has a pH greater than 7 and is capable of neutralizing an acid.
- Neutral- A substance that is neither acidic or alkaline and has a pH of about 7.
- Acid- A substance that has a pH less than 7, a sour taste, and is able to neutralize an alkaline.
- Hypothesis- Making a prediction or educated guess about what you think will happen in the experiment.
- Moderation- The process of limiting or lessening extremes; to do something in control.
- pH- Potential Hydrogen- the measurement of the acidity of alkalinity in a solution
- Students may not leave pH strip in food for a long enough period of time, resulting in an inaccurate measurement of the pH. The strips should be left in the food between 5 to 10 minutes in order to get an accurate reading.
- After learning about pH leveles in foods, the students will put food in order according to how acidic, basic or alkaline they are.
- Students will be able to identify which food is most acidic, basic and alkaline.
- On the handout, students will create a graph to record data on the levels of pH in foods tested.
Buono's book would be read to students to grab their interest and get them thinking about healthy living. This book introduces students to characters that represent both healthy and unhealthy eating choices that can be made. The characters are meant to grab students attention in the same way that fast food and other advertisers do. After the book was finished students would be asked to engaged in discussion about making healthy food choices.
- Buono, Anthony, and Roy Nemerson. The Race Against Junk Food (Adventures in Good Nutrition). HCOM Inc., 1997.
Haduch's book is a combination of creative ways to get students interested on what they are eating. It also contains information in a way that is Representative of the Guinness Book of World Records. The book is intended to get students thinking about the food choices they make on a daily basis. A portion of the book (includes Jokes,Stories,Fun Facts,and many other forms of information) could be read everyday at the start of class and it also could be left out for students to read at their leisure throughout the unit.
- Haduch, Bill. Food Rules! The Stuff You Munch, Its Crunch, Its Punch, and Why You Sometimes Lose Your Lunch. New York: Puffin, 2001.
Science: Body Systems
S3-4:41 Students demonstrate their understanding of Human Body Systems by…
• Showing connections between external and internal body structures and how they help humans survive,
a. There are external and internal structures that provide for the survival needs of human organisms.
- Skin protects the body from harmful substances and other organisms and from drying out.
- The skeletal system provides shape and protection for the body’s organs.
- The brain gets/gives signals from/to all parts of the body “telling” the body what to do.
- From food, people obtain nutrients and other materials for body repair and growth. The un-digestible parts of food are eliminated. Key structures are mouth, esophagus, stomach, intestine and anus.
- By breathing, people take in the oxygen that they need to live. Key structure is the lung.
Welcome to the Vermont Department of Education Web Site! 29 Jan. 2009 <http://education.vermont.gov>.
M3: 24 Analyzes patterns, trends, or distributions in data in a variety of contexts by determining or using “most frequent” (mode), “least frequent,” “largest,” or “smallest.”
M3: 25 Organizes and displays data using bar graphs or tables to answer question related to the data, to analyze the data to formulate or justify conclusions, or to make predictions.
After the original experiment students could test new items for their pH. Students could also test food for other elements such as sugars or fats in their food. Both experiments tend to a further expoloration of healthy eating and the understanding of an important balanced diet. The website www.cyh.com has a great kid friendly idea of what kids should be eating each day. The measurements for a healthy diet are done out in measurements of cups. I think a great way to show this would be to bring in a measuring cup and show students what they should be eating in contrast to what they do eat everyday. Another thing that could extend the lesson is to read the books The Race Against Junk Food (Adventures in Good Nutrition) and Food Rules The Stuff You Munch, Its Crunch, Its Punch, and Why You Sometimes Lose Your Lunch. These books both make great health connections that directly relate to the content of the lesson.
After the completion of the lesson, we discussed what worked well and what was unexpected. What worked well for us was the completion of the handout. The students seemed very interested in figuring out what pH was and where it is most commonly found. Students were eager to test the foods, and successfully identified the levels of pH in their foods. After testing, the students went back to the handout and completed the table. They seemed excited to share their data with their peers. During the lesson, we noticed that we needed a more clear definition of alkaline and an example of what an alkaline is. We also noticed that the table, in which the students were to complete the results of the experiments, was not easily understood by many students. However, we were able to improvise and have the student’s just record the necessary information next to the foods. Many students came into the lesson with no prior knowledge of what pH is. However, when the students were completing the second question on the handout, the majority of them realized that pH is found in pizza, swimming pools and lemon juice, not bowling balls or their homework. Some "must do" components of the lesson are to make sure every student plays a role in the experiment, from testing the foods, to identifying the level of pH, and sharing the data. We believe that the lesson ran very smoothly, even with the short amount of time given to complete the lesson.
Buono, Anthony, and Roy Nemerson. The Race Against Junk Food (Adventures in Good Nutrition). HCOM Inc., 1997.
Dictionary.com. 07 Apr. 2009 <http://www.dictionary.com>.
Haduch, Bill. Food Rules! The Stuff You Munch, Its Crunch, Its Punch, and Why You Sometimes Lose Your Lunch. New York: Puffin, 2001.
"Kids' Health - Topics - Balanced diet." CYH Home - Home. 07 Apr. 2009 <http://www.cyh.com/HealthTopics/HealthTopicDetailsKids.aspx?p=335&np=284&id=1429#3>.
Welcome to the Vermont Department of Education Web Site! 07 Apr. 2009 <http://education.vermont.gov>.