Chemistry Experiment Report

Energy in Foods Practical

Submitted on

November 6, 2014

Submitted by

Yiqin Feng ( Inés )

203537

Submitted to

Mr. Thomas Gray

Energy in Food Practical (Inés)

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Table of Contents

Energy in Foods Practical ............................................................................. 3 Aim—Measuring energy in food .......................................................................... 3 Equipment .............................................................................................................. 3 Method ................................................................................................................... 3 Data ........................................................................................................................ 4 Results ..................................................................................................................... 5 Conclusion ............................................................................................................. 6

Bibliography .................................................................................................. 8

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Energy in Foods Practical

Aim—Measuring energy in food This practical will show a method for calculating the amount of energy contained in various snack foods.

The purpose of the activity is to measure the energy content of different kinds of food by burning the food to warm a known quantity of water. Measure the change in temperature of the water.

Equipment

§ Equipment Number § Bunsen burner 1 § Conical flask 1 § Clamp stand 1 Thermometer (-10°C to 110 °C) 1 § Measuring cylinder (50ml to 100ml) 1 § Mounted needle 1 § Food samples (Popcorn, Peanuts, Fish Snack,

Pistachios, Cheese Ball)

1 pieces for each

§ Water 50ml*5 § Electrical balance 1

Method 1. Use the measuring cylinder to measure 50ml of water into the Conical

flask.

2. Clamp the conical flask to the clamp stand

3. Measure the initial temperature of the water with the thermometer. Record the temperature on a set result table.

4. Choose a piece of food and find its mass using the balance. Record the mass in the table.

5. Impale the piece of food carefully on a mounted needle.

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6. Turn on fire on the Bunsen burner and hold the food in the flame until it catches alight.

7. As soon as the food is alight, put it under the conical flask of water. (Try to make sure that as much of the heat from the burning food as possible is transferred to the water. Do this by keeping the flame under the conical flask

without touching it.)

8. Hold the food in place until the food has burnt completely. If the flame goes out, but the food is not completely burnt, quickly light it again using the Bunsen burner and replace the food beneath the conical flask.

9. When the food stops burning stir the water carefully with thermometer, and measure the final highest temperature reached in the results table.

10. Get fresh water, and repeat using the other snacks.

11. Calculate the change in temperature each time.

Data The table below shows the data(results) of the experiment:

Food sample used

Popcorn Peanuts Fish snack Pistachio Cheese

Ball

Mass of the water (g) 50 50 50 50 50

Mass of the snack 6g/10 pieces

7g/10 pieces

7g/10 pieces

8g/10 pieces

8g/10 pieces

Initial temperature(°C) 18.8 19.0 20.2 21.3 19.8

Final temperature(°C) 31.1 60.9 37.1 64.8 46.5

Change in temperature(°C) 12.3 41.9 16.9 43.5 26.7

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P.S. Using 10 pieces to measure the mass of the snack; the data is more accurate than 1 piece.

Results

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 energy in different foods can be compared using the temperature change per kg. Just divide the temperature change by the mass of food used.

The equation below can be used to find the energy in each food sample.

Energy  released  form  food  per  gram

=4200J/kg°C  ×mass  of  water(kg)×∆T(°C)

mass  of  food  sample  (g)

Energy  per100g = Energy  x  (100/mass  of  the  food)

4200 is the value of the specific heat capacity of water, in joules 1𝑚! per degree Celsius – the number of joules taken to raise the temperature of water by 1 °C. 1 𝑚! of water has a mass of 1 kg.

If the number is more than 1000 J/g, express it as kilojoules (kJ):

1 kilojoule = 1000 joules

The table below shows the comparison of energy contents:

* Energy of popcorn data from USDA Nutrient Database (The National Agricultural Library)

Popcorn Peanuts Fish snack

Pistachio

Cheese Ball

Enegy per 100g from the Label (kJ/100g)

1589

(382 kcal)

2570

(620 kcal)

1880

(446 kcal)

2444

(590 kcal)

2140

(512 kcal)

Enegy per 100g from the TEST (kJ/100g)

431 1257 570 1142 701

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Conclusion If the change in temperature is greater when the water is heated with the use of the fire caught by the food sample. Then the energy content in the food sample is higher because the heat energy is greater, since the heat energy is absorbed by the water when the fire is kept under the test conical flask containing water. The formula indicates that if the change in temperature is greater when the mass of the substances and the volume of water are constant, then the heat energy is higher. In this case peanuts has the greatest energy content. It was burning last more than two minutes. Pistachio has a bigger change in temperature than peanut, because it has a bigger quantity. (0.8g>0.7g) 1. How do your figures compare with the published numbers? My figures are all different from the published numbers and the calculated foods’ energy contents are much more lower than that on the labels from the food package.

2. Why are they different? The reason why most of the figures are much lower than the published numbers may be the following reasons:

1. The food had not been fully burnt during the experiment. There may be some food energy was still inside of the food and had not been released.

2. Heat energy may also cause the losing energy into the air instead of transferred into the water.

All of them together could lead a great difference in food energy content. 3. What should be the published energy value of the popcorn? There is no energy label for the popcorn. A commonly acceptable number is 1589kJ/100g (382kcal). The calorie content has been list on the label, which is also a way to show how much of the energy it contains. A high calorie food

1589

2570 1880

2444 2140

431 1257

570 1142

701

Popcorn Peanuts Fish snack Pistachio cheese ball

comparition of energy Label(kJ/100g) Test(kJ/100g)

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can be a high energy food. 4. What assumptions have we made about the heat from the burning

food? Food will lose the energy that to be transferred to the water that leads the temperature of water to rise. 5. What equipment should we have used to make the experiment more

accurate? 1. Using a lid can as a draught shield to cover the top in order to prevent

heat loss. 2. Using a flee can to cover the whole reaction.

3. Considering use a boiling tube instead of flask. (Library)

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Bibliography Library, T. N. (n.d.). Agricultural Research Service United States Department of

Agriculture. Retrieved from

http://ndb.nal.usda.gov/ndb/foods/show/6352?fg=&man=&lfacet=&format=&co

unt=&max=25&offset=&sort=&qlookup=popcorn.