This activity is an interesting way to engage students before formally beginning the study of Thermochemistry. It involves something that many students will see in their everyday lives, perhaps with parents, relatives, maybe even their body image-conscious friends: the replacement of coffee cream with 1% milk1, in an attempt to consume fewer calories.2
On the surface, this appears reasonable. 1% milk is 1% fat; Half-and-Half cream is, well, much creamier, and hence contains more fat. On closer examination, folks tend to use a much larger volume of 1% milk in a cup of coffee than they would if they used “Half-and-Half” cream, which is 12% butterfat3, in order to get the same “look”—and presumably a reasonably similar taste and mouth-feel in their coffee.
Being a skeptical empiricist, I—and my students—performed an experiment to test the veracity of this claim.
The results are in the accompanying handout.
This assignment gives students experience with energy units: calories and Calories4, and Joules. And the idea that when food is metabolized, energy is released. The assignment will get students to read labels, and in the case of Question 3, to solve a problem using simultaneous equations, a rare event outside of a Mathematics class. Further, it will give students the opportunity to verify—empirically—a claim, that on the surface, sounds reasonable.
This may provoke an interesting discussion.
Afterwards, we move on to the study of the ΔHvap and ΔHfusion of water, using data obtained in our lab. The energetics involved in these phase changes—physical changes—brings students to the point where they can intelligently discuss enthalpy changes in chemical reactions, aka Thermochemistry.
- 1% butterfat
- I saw this with several colleagues
- What Is Half-and-Half and What's a Good Substitute? (allrecipes.com)
- Food Calorie (upper case “C”) = 1000 calories; 4.184 J = 1 calorie; 4.184 kJ = 1 C
This experiment requires about 30 minutes, working as a group.
coffee cups for mixing and taste testing
half & half cream
stir sticks / spoons
sugar / sweetener if desired
- Students experiment to find the amount of 1% milk required to give the same "look" and mouth-feel as 3 tablespoons "half & half" in a cup of coffee. You can do this in class if you have time to spare or you can ask volunteers to experiment at home. However, you are welcome to use data gathered by a small group of my own AP students if experimentation is not possible: 9 tablespoons 1% milk / cup of coffee gave the same “look” and mouth-feel as 3 tablespoons “half & half” / cup of coffee .
- Using the nutrition labels listed in the handout or those provided by you, students use their data to answer a series of questions.
Note: For safety reasons, experimenting with taste testing coffee should not be performed within the designated laboratory space.
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Pull together materials for experimenting to find the best amount of 1% milk required to have the same look and feel of half & half cream or provide students with sample data.