Energy Content of Foods Computer



Energy Content of Foods

All human activity requires “burning” food for energy. In this experiment, you will determine the energy released (in kJ/g) as various foods, such as cashews, marshmallows, peanuts, and popcorn, burn. You will look for patterns in the amounts of energy released during burning of the different foods.

BACKGROUND

WHEN BURNING FOOD WARMS A KNOWN QUANTITY OF WATER, THE AMOUNT OF THERMAL ENERGY GIVEN OFF BY THE FOOD IS THEORETICALLY EQUAL TO THE AMOUNT OF THERMAL ENERGY GAINED BY THE WATER. THE FOLLOWING IS AN EQUATION THAT DESCRIBES THIS IDEA:

Q = M X C X ∆T

WHERE Q IS THE AMOUNT OF THERMAL ENERGY, M IS THE MASS OF WATER, AND C IS THE SPECIFIC HEAT OF WATER, AND ∆T IS THE CHANGE IN TEMPERATURE OF THE WATER.

THE SPECIFIC HEAT, C, OF WATER IS:

C = 1 CALORIE GRAM-1°C-1 = 4.186 J GRAM-1°C-1

IN THIS ACTIVITY, BURN A SAMPLE OF FOOD UNDER A CONTAINER OF WATER TO HEAT THE WATER. MEASURE THE CHANGE IN TEMPERATURE OF THE WATER AS IT IS HEATED BY THE BURNING FOOD. COMPARE THE AMOUNT OF HEAT GIVEN OFF BY A DIFFERENT TYPE OF FOOD.

[pic]

Figure 1

MATERIALS

|SPARK DATA COLLECTION |2 UTILITY CLAMPS |

|3” X 3” CARDBOARD SQUARE |25 ML GRADUATED CYLINDER |

|ALUMINUM FOIL |RING STAND |

|TEMPERATURE PROBE |100-ML GRADUATED CYLINDER |

|TWO FOOD SAMPLES |LARGE TEST TUBE |

|DISSECTION PIN |COLD WATER |

|WOODEN SPLINT |MATCHES |

PROCEDURE

1. OBTAIN AND WEAR GOGGLES.

2. Construct food holder by pressing a dissection pin through a 3”x 3” piece of cardboard. Press aluminum foil own over the dissection pin to cover the cardboard.

3. Obtain a piece of one of the two foods assigned to you. Find and record the initial mass of the food and the food holder. CAUTION: Do not eat or drink in the laboratory.

3. Accurately measure approximately 25 mL of cold water and add to the test tube. Using the density of water, 1 g/mL, record the mass of water.

4. Set up the apparatus as shown in Figure 1. Use a ring stand and an utility clamp suspend the test tube about 2.5 cm (1 inch) above the food sample. Use a utility clamp to suspend the Temperature Probe in the water. The probe should not touch the bottom of the test tube. Remember: The Temperature Probe must be in the water for at least 30 seconds before you do Step 6.

5. Prepare the SPARK for data collection by plugging a temperature probe into the port on the top of the SPARK. Turn power on the SPARK. Press OPEN. Press SUBJECT. Select the category labeled CHEMISTRY. Scroll down and select, ‘ENERGY CONTENT IN FOOD’. On the screen, a temperature vs. time graph should appear and a digital reading of temperature.

6. Press [pic] to begin measuring initial temperature of the water. Remove the food sample from under the test tube and use a wooden splint to light it. Quickly place the burning food sample directly under the center of the test tube. Allow the water to be heated until the food sample stops burning. CAUTION: Keep hair and clothing away from open flames.

7. Continue recording temperature data for 45 seconds after the food stops burning or the water until the temperature stops rising. Record the final temperature. Press [pic] to end data collection.

7. Press the graph icon to view tools menu. Select auto scale icon to scale the graph. Press the statistics icon from the same menu. Choose minimum and maximum from the menu and select OKAY. The graph will reappear with minimum and maximum values. These values will correlate to the initial and final water temperatures, respectfully. Record these temperature values. Press the graph icon to remove the menu.

8. Determine and record the final mass of the food sample and food holder.

10. Repeat the procedure for the second food sample. Use a new 25-mL portion of cold water and clean food holder. Each trial will be color coded on the graph. Particular trail runs can be observed by selecting the appropriate run in the legend box in the upper right hand corner of graph.

11. When you are done, place burned food, used matches, and partially-burned wooden splints in the container provided by the teacher.

PROCESSING THE DATA

1. FIND THE MASS OF WATER HEATED FOR EACH SAMPLE.

2. Find the change in temperature of the water, (t, for each sample.

3. Calculate the heat absorbed by the water, q, using the equation

q = Cp•m•(t

where q is heat, Cp is the specific heat capacity, m is the mass of water, and (t is the change in temperature. For water, Cp is 4.18 J/g°C. Change your final answer to kJ.

4. Find the mass (in g) of each food sample burned.

5. Use the results of Step 3 and 4 to calculate the energy content (in kJ/g) of each food sample by dividing the heat energy by the mass of the food burned.

6. Record your results and the results of other groups in the Class Results Table. Which food had the highest energy content? The lowest energy content?

7. Food energy is often expressed in a unit called a Calorie. There are 4.18 kJ in one Calorie. Based on the class average for peanuts, calculate the number of Calories in a 50-g package of peanuts.

8. Two of the foods in the experiment have a high fat content (peanuts and cashews) and two have a high carbohydrate content (marshmallows and popcorn). From your results, what generalization can you make about the relative energy content of fats and carbohydrates?

Extension

1. IN THIS LAB, THE THERMAL ENERGY ABSORBED BY THE TEST TUBE WAS NEGLECTED. WHAT EFFECT WOULD THE ENERGY ABSORBED BY THE TEST TUBE HAVE ON THE CALCULATED ENERGY CONTENT OF THE FOOD?

2. USING THE DATA COLLECTED, CALCULATE THE SPECIFIC HEAT OF EACH FOOD TYPE.

DATA AND CALCULATIONS

|FOOD TYPE |––––––––––––––––––– |––––––––––––––––––– |

|INITIAL MASS OF FOOD AND HOLDER |G |G |

|FINAL MASS OF FOOD AND HOLDER |G |G |

|MASS OF FOOD BURNED |G |G |

|ML OF WATER |ML |ML |

|MASS OF WATER (DENSITY = 1 G/ML) |G |G |

|FINAL TEMPERATURE, T2 |°C |°C |

|INITIAL TEMPERATURE, T1 |°C |°C |

|TEMPERATURE CHANGE, ΔT |°C |°C |

|Heat, q | | |

| | | |

| | | |

| | | |

| |kJ |kJ |

|Energy content in kJ/g | | |

| | | |

| | | |

| | | |

| |kJ/g |kJ/g |

class results table

|MARSHMALLOWS |PEANUTS |CASHEWS |POPCORN |

|KJ/G |KJ/G |KJ/G |KJ/G |

|KJ/G |KJ/G |KJ/G |KJ/G |

|KJ/G |KJ/G |KJ/G |KJ/G |

|KJ/G |KJ/G |KJ/G |KJ/G |

|KJ/G |KJ/G |KJ/G |KJ/G |

Average for each food type

|kJ/g |kJ/g |kJ/g |kJ/g |

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Note: Use test tube and utility clamp, instead of can and ring clamp.

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