1152 lab manual exp10

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Experiment 10- Calorimetry of Foods

Introduction

Animals obtain the energy necessary for life from food. Food is oxidized to

carbon dioxide and water with an associated release of energy. Fortunately for us, our

cells convert much of this energy into useful work, instead of releasing all of it as heat.

Using glucose as an example, nearly half of the energy content of glucose is converted to

useful energy in our bodies. In contrast, a car engine converts less than 10% of the

energy content of gasoline into mechanical energy and releases the rest as heat.

Hess' Law tells us that in going from a specific reactant to a specific product, the

same amount of energy will be released (or consumed) regardless of the pathway. Most

of the carbon atoms in a peanut, for example, will be oxidized to carbon dioxide and

water in our bodies- providing a certain number of calories of energy. The same amount

of energy is released by burning the peanut to produce these same products. This heat

can be used to heat a known mass of water. The temperature change of the water can be

used to calculate the amount of energy added to the water. Since the energy added to the

water came from the combustion of the peanut, we know how much energy was released

from the peanut assuming all of the energy was transferred.

Different types of foods have different energy contents. Glucose has

approximately 4 Calories of energy per gram. Fat (triglycerides) on the other hand have

about 9 Calories per gram. Ethanol has 7 Calories of energy per gram. A nutritional

Calorie (listed on food labels) is 1 kcal or 1000 calories. Foods with a high fat content

will be most effective in this experiment.

Apparatus

Suspend a 12 oz. soda can on a ring stand as shown below.

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Experiment 10

Laboratory Record Name:_______________________

Sample # 1: (be specific) __________________________________

1. mass of water __________ grams

2. mass of sample __________ grams

3. temperature of H2O after burning __________ C

4. temperature of H2O before burning __________ C

5. change in temperature of the H2O __________ C

6. total energy content of sample:

(show calculations below) __________ kcal

7. energy content per gram of sample __________ kcal/gram

Calculations:heat (in cal)= (specific heat of water) x (mass of water) x (change in temperature)

Note that:

(specific heat of water= 1.00 cal/g C)

(1 kcal = 1000 cal)

Sample # 2: (be specific) __________________________________

1. mass of water __________ grams

2. mass of sample __________ grams3. temperature of H2O after burning __________ C

4. temperature of H2O before burning __________ C

5. change in temperature of the H2O __________ C

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6. total energy content of sample:

(show calculations below) __________ kcal

7. energy content per gram of sample __________ kcal/gram

Calculations:

How does your experimental value for each of the samples compare to the energy value

listed on the label?

If 100 mL of water is used in the can (instead of 50 mL), will the experiment still give

accurate results? Explain.

If only a small portion of a peanut (say one-fourth of a nut) is used, will the experiment

still give accurate results? Explain.

Other than mistakes, suggest at least 3 factors that affected the accuracy of your results.

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1152 lab manual exp10

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