Rationale
We eat food for two physiologic reasons: energy and chemical building blocks1. Food undergoes several complex reactions in the digestive system before it is absorbed by the walls of intestine. Some knowledge of chemistry is critical to understanding the metabolism of food in our body.
Metabolism is the complete set of chemical reactions that occur within the cells of our bodies. These reactions extract energy from food, and convert it into movement, growth, and reproduction. Metabolism of carbohydrates is different from metabolism of protein and fat, and vice versa. With the help of this knowledge one can choose healthy food from the abundant varieties available to satisfy one's palate and lead a healthy life. On the other hand, poor food choices lead to overweight and obesity. Being overweight or obese increases the risk of many diseases and health conditions, including hypertension (high blood pressure), osteoarthritis (a degeneration of cartilage and its underlying bone within a joint), dyslipidemia (for example, high total cholesterol or high levels of triglycerides), type 2 diabetes, coronary heart disease, stroke, gallbladder disease, sleep apnea and respiratory problems, and some cancers (endometrial, breast, and colon)2.
This unit will focus on food facts, information on the nutritive values of food, and the connection of this information through stoichiometry. In the normal mode of teaching stoichiometry, I might ask a common question from industrial chemistry: "How many grams of ammonia can be produced by mixing 2.50 kg of nitrogen with excess hydrogen?" To solve this problem students require chemistry knowledge along with simple arithmetic knowledge and problem solving skills. I would like to highlight my student's responses before I discuss the process: 'Again math, are we in math class?', 'Involves many steps, I can't do it', 'It's very hard', 'Too many conversions, I am giving up.' Probably, these types of responses are common in high school chemistry class. I do not want to blame my students totally, because, in truth, the above question does involve several steps. Not only that, they can not relate the above question to their day-to-day life. Though the above process is very important to industry as 20,000 tons of ammonia is used every year in United States for making fertilizers,3 it is not interesting to my students.
The following steps are involved in solving the above question:
- Writing correct formulas for nitrogen, hydrogen and ammonia.
- Writing a chemical equation for the process.
- Balancing the equation.
- Converting the mass of given substances to moles using molar mass of substance.
- Using the stoichiometric coefficients from the balanced equation to convert the moles of given to moles of unknown.
- Converting the moles of unknown to mass of unknown.
- Making sure the mass of unknown is in correct unit with correct significant digits.
The unit focuses on achieving these same problem solving skills by using examples related to food. Hopefully, by selecting problems in which students care about the answers, they will be motivated to use math in chemistry.
I would like to show an example in order to achieve this goal. The problem: "How much energy did you gain from your breakfast/lunch, today?" Students can relate this question to their life. The question can be modified according to your situation and the time of the class. The above question works as it is for first block or the block after lunch. I would modify the question as "How much energy will you get from your lunch, today?" for the block before lunch. This question looks simple and doable to students because they relate it to themselves, though this problem involves many steps too. Since they can relate it to their life they do not mind doing this multi-step math problem. Besides doing math, they need to list the food items, collect facts, analyze the food for nutritive values, put them together, etc. I guess the driving force here is they will know the calories they got from food they had or are going to have, which will be an immediate connection to their life.
The following steps are involved in calculating the total energy from breakfast/lunch:
- Collecting facts: energy per gram of fat, per gram of carbohydrate, and per gram of protein.
- Listing the food items they had/going to have.
- Estimating the number of servings of each food item.
- Collecting the nutrition labels or nutrition facts from the internet for each food item.
- Using nutrition facts, calculating the amount (in grams) of fat based on the servings for each food item.
- Repeating step 5 for carbohydrates and proteins separately.
- Converting grams of fat into energy calories for each item.
- Repeating step 7 for carbohydrates and proteins separately for each food item.
- Making sure that if 3 different food items have consumed, then there are 9 different calorie amounts.
- Adding the caloric amounts obtained in step 7 and 8.
Though this problem is also a multi-step problem and involves math, the students do not mind because the end product of the problem is related to them. After the calculations are done we will have a class discussion and be able to make a list of good foods they had or will have. Hopefully, with this activity students' awareness about healthy food will increase in addition to analytical and problem solving skills. Those skills are essential to stoichiometry. After completing this activity, I would like to bring up the synthesis of ammonia problem. As students are familiar with multi-step problem solving with food analysis, they will do the stoichiometry with no difficulty.
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