Energy Content of Foods

Using ScienceWorkshop temperature sensor

Eq. 1) calories = DT (temperature) x 100         Eq. 2) kcal = calories   Eq.3) kcal per gram = kcal

                                                                                                1000                                        Dgrams of sample masss

Background

When burning, food heats a known quantity of water, the amount of heat given off by the food is theoretically equal to the amount of heat gained by the water. This assumes that 100% of the enerrgy released during the burn is transferred to the water.  The following equations describe this idea: IMPORTANT NOTE: (D means “change in”)

One calorie is the amount of heat required to raise the temperature of 1 mL of water by 1 degree C.  You will measure the amount of change in temperature of 100 mL of water while burning a food sample.  Therefore, you must multiply your change in water temperature by 100. Calorie values on food nutrition labels are actually given as kilocalories (Kcals) where 1000 calories = 1 Kcal. 

CAUTION: Keep hair, clothing, and other items away from open flames.

  1. The set up the equipment will be similar to that shown on pg. 702. This diagram has several differences compared to our set up.  Listen carefully to your teacher.   Start up ScienceWorkshop, dragging the analog plug icon to channel A and selecting the first Temperature Sensor as you scroll down.  Open a graph by clicking on the graph icon and then dragging it to the thermometer icon. Also open a table by clicking on the table icon and dragging it to the thermometer icon. You do not need to calibrate the Temperature Sensor.  Move both the graph and the table away from top left hand corner of he interface icon so you can start and stop each data collection run.
  2. Measure out 100 mL of water using the graduated cylinder and pouring it into the flask.  Push the stopper and probe into the flask.

3.      Zero or tare the balance before you attempt to measure the initial mass of the food sample that will be burned.

4.      Use a lighter to ignite your food sample it will probably be best to have it  already in position inside of the can.

5.      Be sure the burning food sample is directly under the center of the container. Start recording data, by clicking rec.

6.      Watch the data on the graph.  The sample will eventually burn out.  However, keep recording until the temperature data remains stable/ starts to decline. To know when this is, watch for the numbers on the table to remain the same /start declining.  Press the “stop” button to stop recording data.

 

Equipment Needed:                        

Computer, interface and temperature sensor              100 mL graduated cylinder

Slit stopper                                                        250 mL flask

Balance                                                              Lighter             

tongs                                                                 Food holder

tweezers

aluminum foil                                                     3 walnut halves

Protective gear                                                    3  shelled and skinned whole peanuts

Container (metal can)                                           3 cashew  halves (not whole)