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Cheeto Lab: Calories in Food

Introduction/Background Information:

Food has potential energy stored in the chemical bonds. When we eat food, the potential energy is converted into chemical energy. All human activity requires “burning” food for energy. The body uses the chemical energy from foods to maintain body temperature, to contract muscles, and to repair tissues. Any excess energy is stored as fats. Food energy is often expressed in a unit called a Calorie. There are 4186 J in one food Calorie. Not all types of food release the same quantity of energy in calories when they burn or are metabolized. Whether food is fat, protein, or carbohydrate makes a difference in calorie counting. Most of the energy we need comes from carbohydrates and fats. Carbohydrates produce 17,000 J/g while fats produce 38,000 J/g. Proteins produce 17,000J/g. In this experiment you will determine the energy released (in J/g) as snack foods burn.

Materials: Calorimeter, burner, tongs, graduated cylinder, thermometer, balance, metal wire, cork, watch glasses, Cheetos.

Purpose: In this laboratory investigation, you will determine the amount of calories contained within two Cheeto samples.

Pre-Lab:Complete these questions by looking at the nutritional information on the back of the package.

  1. How many and what types of Calories are reported to be in one gram of Cheeto?
  1. According to the number of Calories/gram, what would be the change in temperature to 100 mL of water, heated by burning one gram of Cheeto? (Show your work.)

Safety: There will be open flames in the lab. Make sure that your hair and loose clothing is pulled back, so they do not come in contact with the flames. Wear your goggles at all times. Make sure that all flames are extinguished before leaving the lab area.

Procedures:

1. Set up the calorimeter as demonstrated by your instructor.

2. Obtain one Cheeto. Skewer the Cheeto on the wire/cork rig, and place the rig on a watch glass. (It might be necessary to bend the wire and/or wrap the wire around the Cheeto so that it won’t fall off during combustion.) Mass this watch glass/Cheeto system.

3. In a graduated cylinder measure 100.0 mL of water (Sig figs note: if the bottom of the meniscus in the cylinder is exactly on the 100 mL line, you have 100.0 mL. Why should this be the same for each trial?) Pour the water into the calorimeter.

4. Use the thermometer to record the beginning temperature of the water. (Remember sig figs!)

5. Place the watch glass/Cheeto system under the calorimeter. Carefully light the Cheeto on fire with the burner and hold the burning food directly beneath the calorimeter (pay attention to the distance below the calorimeter—should you control this variable?). Use the thermometer to record the highest temperature the water in the calorimeter reaches after the food stops burning.

6. After the sample stops burning, record the final mass of the watch glass/Cheeto system.

7. Replace the water in the calorimeter with 100.0 mL of fresh water. Repeat the measurement for another sample.

Data:

Trial
Initial Mass (m0)
Final Mass (mf)
Initial Water Temperature (T0)
Final Water Temperature (Tf)

Calculations:Show all of your work in the spaces below. Draw a box around your final answer.

  1. For each sample, determine how many Joules were absorbed by the water.
  1. Given the energy absorbed by the water and the change in sample mass, determine the energy content in Joules/gram for each sample.
  1. Convert the two values determined in #2 to energy content in terms of Calories/gram.
  1. Perform percent error calculations for each sample as compared to the number of Calories/gram reported on the Cheeto packages.

Conclusion:

  1. If the observed temperature change in the water was different from the temperature change predicted in Pre-Lab Question #2, how was it different and why?
  1. What improvements could you make to this lab to improve its accuracy?