Caloric Content of Food

The objective of this lab is to estimate the caloric content of various food samples by conducting a calorimetry experiment. Through this experiment, students will gain practical experience in using tools and equipment for scientific analysis and research, demonstrating safe practices in the chemical laboratory, estimating caloric content, understanding the composition of matter and energy, recording investigation results, using scientific reasoning to evaluate phenomena, and identifying the unifying themes in the scientific field of study.

In the discussion, it is explained that a calorie is a unit of energy and is commonly used to measure food energy. One calorie is equal to the amount of energy required to raise the temperature of 1 gram of water by 1°C. Food calories, as read off nutrition labels, are actually kilocalories (often denoted as "Calories" with a capital C), where 1 kilocalorie is equal to 1,000 calories or food calories.

A calorimeter is a device used to measure the energy released or absorbed during a chemical reaction or phase change. In the context of food calorimetry, a piece of food is burned, and the released energy is used to heat a known quantity of water. The resulting temperature change of the water is used to determine the energy content of the food.

The procedure involves obtaining 50 mL of water in a beaker and determining its mass. A ring stand with a Bunsen burner is set up, and a 2-3 gram sample of food is placed on a wire mesh above the burner. A thermometer is suspended in the water, and the initial temperature is recorded. The Bunsen burner is lit, and the food sample is burned, heating the water. The temperature change of the water is monitored and the highest observed temperature is recorded. The remaining mass of the food sample is determined. These steps are repeated for each food sample.

The calculations involve using the calorimetry equation Q = mCpΔT, where Q is the calculated energy released by the burning food sample and absorbed by the water, m is the mass of the water, Cp is the specific heat of water (1.00 cal/g ∙ °C), and ΔT is the change in water temperature. The kilocalories/gram of each food sample is determined by calculating the number of kilocalories released by the burning food sample and dividing it by the grams of food consumed during burning. The experimental value of energy content per gram is compared to the actual value obtained from the nutrition label of the food sample. The percent error is calculated by comparing the experimental and actual values.

Through this lab, students gain practical experience in measuring energy content using calorimetry, understanding the concept of food calories, conducting calculations, and analyzing the energy content of different food samples. It also reinforces the importance of accurate measurements, understanding energy conversions, and interpreting nutrition labels.

Objective

·         Use the tools and equipment necessary for basic scientific analysis and research

·         Demonstrate safe practices in the Chemical Laboratory

·         Demonstrate how to Estimate the Caloric Content of Peanuts and other food groups

·         Demonstrate the proper use of Exponential Notation and Significant Figures

·         Demonstrate an understanding of the composition of matter and energy

·         Record the results of investigation through writing

·         Use scientific reasoning to evaluate physical and natural phenomena

·         Identify the unifying themes of the scientific field of study

Materials

·         Glassware

·         Ring stand

·         Bunsen burner

·         Combustible food

Discussion

A calorie, like a joule, is a unit of energy. The International System of Units (SI) unit for energy is the joule; however, the calorie is commonly used for a unit of food energy. A calorie is equal to the amount of energy per unit Mass required to raise the temperature of 1 g of water by 1° C. One calorie is the equivalent of 4.18 joules. Food calories, as read off a nutrition label, are actually kilocalories (often denoted as “Calories” with a capital C). There are 1,000 calories in a kilocalorie, or food Calorie.

A calorimeter shown in figure 20 is a piece of equipment designed to measure the energy released or absorbed during a chemical reaction or phase change. Food calorimetry allows us to determine the number of calories per gram of food. in this activity, a piece of food is burned and the released energy is used to heat a known quantity of water. The temperature change (∆T) of the water is then used to determine the amount of energy in the food.

Note. Figure 20 shows an Open-Air Calorimeter which is less accurate than a Bomb Calorimeter

Procedure

1.       Using the graduated cylinder, obtain 50 mL of water and carefully pour it into a 50 mL beaker

2.       Determine the Mass of water and record your finding in the data table (hint: density of water = 1 g/mL).

3.       Position ring on stand so the Bunsen burn fits under it, then place mesh on ring.

4.       Obtain a 2- to 3-g food sample.

5.       Determine the initial Mass of the food sample and record your findings in the data table.

6.       Place the food sample on the wire mesh.

7.       Make sure the space has been cleared of all flammables.

8.       Adjust the ring stand until the beaker is approximately 4 cm above the food sample.

9.       Suspend the thermometer inside the beaker a few centimeters above the beaker's bottom. Determine the initial temperature of the water in the can and record this value in the data table.

10.   Carefully light the Bunsen burner and use it to light the food sample.

11.   Allow the lit sample to heat the water in the can. Gently stir the water periodically with the stir rod

12.   Monitor the temperature change of the water and record the highest observed temperature in the data table

13.   Once the food sample has burned, find the Mass of the remaining food sample. Record this value in the Report Sheet.

14.   Repeat steps 1 through 14 for each of the remaining food samples.

Calculations

Calorimetry Calculations for each food sample

Q = mCpΔT

Where:

m =   Mass of the water in Grams (mL=g water)

Cp = 1.00 cal/g ∙ °C (specific heat of water = 1)

∆T = Change of water temperature from the initial temperature to the final temperature, ∆T.

Tf – Ti = ∆T

Q = Calculated energy (in calories) released by the burning food sample and absorbed by the water.

Kilocalories/gram Calculations for each food sample

1.       Determine the number of kilocalories (KCal), food Calories, released by the burning food sample (1 kilocalorie, or Calorie = 1,000 calories).

2.       Grams of food consumed during burning

Massi of food - Massf of food

3.       Calculate the experimental value of energy content of the food in kilocalories/gram. 

4.       Calculate the actual value using information on the nutrition label of the food sample, calculate the kilocalories/gram. (Divide Calories per serving by the number of Grams in a serving.)

5.       Calculate %error by comparing your experimental value of energy content (in kilocalories/gram) to the actual value from the nutrition label.

Calculate the percent error for your experiment. 

% error = |(Actual Value - Experimental Value) / Actual Value | x 100

Name_______________________________________                

Date___________________________

Lab / Section_________________________________

Report Sheet for CALORIC CONTENT of FOOD

Review Questions

1.       What is the purpose of conducting the calorimetry experiment in determining the caloric content of food?

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2.       Explain the difference between a calorie and a kilocalorie (Calorie).

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3.       How does a calorimeter work? Describe its role in measuring energy released or absorbed during a chemical reaction.

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4.       Why is it important to record the initial and final temperatures of the water in the calorimetry experiment?

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5.       What is the specific heat capacity of water? How does it affect the calculations in calorimetry?

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6.       Describe the steps involved in setting up and conducting the calorimetry experiment.

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7.       What is the significance of using a known quantity of water in the calorimetry experiment?

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8.       How does the burning of food samples relate to the measurement of energy content?

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9.       Explain how the change in water temperature is used to calculate the energy released by the burning food sample.

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10.    What are the units used to express energy content in the calorimetry experiment?

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11.    How can the experimental value of energy content per gram be compared to the actual value obtained from the nutrition label of a food sample?

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12.    Discuss the factors that may contribute to potential errors in the calorimetry experiment and its calculations.

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13.    Why is it necessary to repeat the calorimetry experiment for each food sample?

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14.    How does the mass of the remaining food sample affect the calculations of energy content?

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15.    Describe the process of determining the kilocalories/gram for each food sample in the experiment.

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16.    Discuss the importance of accurately measuring the mass of water and food samples in the calorimetry experiment.

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17.    Explain how the percent error is calculated in relation to the experimental and actual values of energy content.

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18.    What are some potential sources of uncertainty in the calorimetry experiment? How can they be minimized?

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19.    Discuss the practical applications and significance of determining the caloric content of food.

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20.    Reflect on the overall learning outcomes and skills developed through conducting the calorimetry experiment.

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