Determining Caloric Content of Food. Sudha Madhugiri, Ph.D. Collin College Department of Chemistry

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1 Determining Caloric Content of Food Sudha Madhugiri, Ph.D. Collin College Department of Chemistry We all know that food gives us energy. Some foods are tastier but are not so healthy. Some foods help you sustain longer and at the same time are healthier. If the human body is compared to an engine, food is the fuel used to run that engine. In this experiment we are going to evaluate the energy content, also known as caloric value, of some food items. Caloric value of foods is typically measured using a highly technical apparatus, called a bomb calorimeter. However, we will be using a simpler apparatus made with easily available materials such as empty soda cans and thermometers. The idea here is, when food is burned it produces energy, which is used in our physiological activities. In a lab, the same energy can be used to heat a measured sample of water, and the energy transferred to water can be calculated. Assuming no heat was lost to the surroundings, this would be the same as the caloric content of the food. Each substance requires a specific amount of energy to raise the temperature by a given amount. This is called specific heat. The specific heat of water is J/g o C. This means that for each gram of water, it takes J of energy to raise its temperature by 1 o C. So, we can calculate the heat (q) produced by the food by using the following equation: Heat absorbed by the water sample (q) = massh2o * specific heat of H2O * T Specific heat of water = J/g o C T = difference in temperature of the water sample, [Tfinal - Tinitial] Based on the law of conservation of energy, energy is neither created nor destroyed. Hence, the heat released by the food is the same as the heat absorbed by the water, provided no heat is lost to the surroundings. This can also be stated as: Heat absorbed by the water sample = Heat released by food Caloric content of food is normally represented using a Calorie (with a capital C ) which is equal to 1000 cals, also known as a kilocalorie (kcal). In this experiment you will measure the caloric content of different food materials and compare your measurement with the caloric content reported by the manufacturer.

2 Experiment: Part I: Caloric content of Popcorn 1. Set up the experiment in a fume hood as shown in figure Obtain an empty soda can and set up the can using a ring stand as shown. Set up a thermometer making sure that the bulb is immersed in the water sample. 3. Pour 50 ml of water into the can. Measure and record the initial temperature of the water sample, Tinitial 4. Weigh and record the mass of an empty evaporating dish. 5. Weigh approximately 1.0 g of popped corn and place them in the previously weighed evaporating dish. Place the evaporating dish below the soda can containing water. 6. Now ignite the popcorn with a lighter or a match stick. Adjust the height of the can to be as close as possible to the burning popcorn. This is to minimize the loss of heat to surroundings. If the flame goes out, re-light the popcorn. 7. When the popcorn is completely burned, stir the water until the temperature stops rising and record the final temperature of the water sample, Tfinal. 8. Let the evaporating dish cool down and determine the mass of the dish with the ashes and any unburned popcorn that is left over. 9. Enter the data in your report and perform necessary calculations. 10. Look up the caloric content on the bag of popcorn and compare your calculations with the reported value. Enter all the calculations in detail on your report sheet. Figure 1: Experimental Set Up

3 Part II: Caloric Content of a Marshmallow: Repeat steps 1-10 from Part I of the experiment using Cheetos and perform all necessary calculations. Tip: When the mass of the food material is determined it is not critical to get an exact mass of 1.0 g. Record the actual mass used for the experiment which can be around 1.0 g. Prelab Questions: 1. Define specific heat? 2. a) What is the amount of energy needed in joules to raise the temperature of 250 ml of water from 22 o C to 45 o C? (Density of water is 1.00 g/ml and specific heat of water = J/g o C) b) Convert the energy in problem 2a to kcals (Cals). 3. A 0.50 g sample of vegetable oil gives out 19.9 kj of heat when burned. What is the caloric value of the oil in kcal/g? 4. A high protein diet provides 50.0 g of carbohydrate, g of protein, and 7.0 g of fat. How many nutritional Calories (1 Cal = 1kcal) does this diet provide? Consider these caloric values for your calculations. Food Type kcal/g Carbohydrate 4 Protein 4 Fat 9 5. What is the formula for calculating error%?

4 Name: Date: Determining Caloric Content of Food - Report Sheet Use appropriate units and show all calculations wherever necessary. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) Food sample tested Mass of the food material before heating Mass of the food material (ashes) left after heating Mass of the food material burned (b-c) Volume of the water sample Mass of the water sample (Density of water is 1.00 g/ml) mass (g) Density = Volume (ml) Initial temperature of the water (Tinitial) Final temperature of the water after heating (Tfinal) T [Tfinal - Tinitial] Heat absorbed by the water sample in joules (Show your calculation) q=massh2o * specific heat of water * T (specific heat of water = J/g o C) Part I Part II (k) (l) (m) Heat absorbed by water in kcal (or Cal) (Convert Joules from step (j) to Calories and then to kilocalories) Caloric content of the food: Cal/g (use the mass of the food material burned) (Show your calculation) (Step k/step d) Caloric content of the food: Cals/serving (Refer to manufacturer s serving size)

5 (n) (o) Manufacturer s caloric content Cals/serving: (printed on the bag) % Error Post lab Questions: 1. Was heating the water sample an endothermic or an exothermic process? Explain. 2. Based on the net heat calculation from burning food, was this process endothermic or exothermic? Explain. 3. Was your experimentally determined caloric content per serving the same as the manufacturer s caloric content? Why or why not?