Acid, Base, pH and Food Chemistry

I try to examine activities an multiple levels. First on the list, I want to know if my students will be engaged and learn something. Second, how difficult is it for me as a teacher to actually pull it off? One of the most important questions...are the students learning chemistry or just having fun? This is the first year I have attempted the following activity. Students were engaged in the real world connection, they asked questions, it transitioned into some chemistry concepts and even some parents got involved. The activity involved acid, bases, pH and food.

Last year I had the honor of meeting Dr. Janet Marshall from Miami University Ohio at a regional ACS meeting. Dr. Marshall teaches classes that involve food, chemistry and biochemistry. She actually received a grant to turn half of her chemistry lab into a kitchen. She shared a lab with us that involved chocolate muffins and chemistry (how can you not like this?). Here is the essence of the lab. Students have the chance to make three different types of chocolate muffins.  ust before they cook each of the batches they take some of the batter and test the pH. Each batch has a slightly different pH. One batch is slightly acidic (version #1). Another batch is slightly basic (version #3). This has an impact on the muffins. As it turns out, American cocoa can act as a levening agent and is slightly acidic. In version #1 there were more ingredients to react with the acidic cocoa and the muffins turned out a bit more dense in texture with a slightly different flavor. As the recipes changes  the cocoa has a chance to act more as a levening agent. The texture of the muffin changes (more "fluffy") as does the flavor. Dr. Marshall in an email correspondence was able to explain it much better...

"For the chocolate cake/muffins variations, version #1 was the most acidic (batter pH ~ 6) and version #3 was more alkaline (batter pH ~8). The reason has to do with the acidic/basic ingredients used to leaven the cake.  Specifically, American cocoa is rather acidic (pH ~5) due to the fermentation process. The ethanol produced during fermentation is oxidized to acetic acid so the cocoa provides a source of acid. The milk (either buttermilk or whole milk) also provides an acid source, primarily in the form of lactic acid (more in buttermilk). The baking soda (sodium bicarbonate) used in versions #2 and #3 reacts as a base to neutralize these acids. Lastly, the baking powder is balanced in terms of acid/base. Therefore, in version #1, the key acid/base ingredients are buttermilk, cocoa, and baking powder. The baking powder is essentially neutral and there is not an alkaline ingredient (such as baking soda) to counter-balance the acidic buttermilk and cocoa.  Therefore, version #1 is the most acidic of the three options. I hope this helps answer your question. I adapted these recipes from "How Baking Works" (reference provided on the handout) to develop this lab experiment.  - " May 21st 2017

So here is how the activity played out in the classroom: It was the last two weeks of school just after prom, after weeks of AP and state testing and I was trying hard to teach as summer was approaching and the weather was improving. I had never done this activity so I introduced it as an extra credit activity. Kids could cook these at home and I would need a picture of them with a parent or guardian to make sure they did not just buy some at the store. They would come in and we would "eat" the experiment. I also pulled in the current issue of "Chemmatters" and we served different coffees and tested the pH. Given the onslaught of previous testing the students had just survived most of the "assessment" questions were informal. We just sat around, drank coffee and ate muffins while talking about the acid base chemistry of it all and how pH can change texture and taste. I have several students who like to cook and I think appreciated the break from traditional work. Overall, I would consider it a success. I will post the lab from Dr. Marshall. I do not have a "key" because we did this more as an activity. Let me know what you think.