Introduction: (Initial Observation)
After we eat food, it will be digested in our stomach. Digestion is a process in which enzymes and mechanical actions of stomach modify the food and make it absorbable for our body. Food which is the source of energy for us will finally burn slowly and change to heat. That is the heat that keeps us warm and is needed for our body to survive. Some foods can deliver more energy than others.
Although the mechanism and chemical reactions of burning food in our body is very different from burning solids in the air, the amount of heat energy released in both case are close. In this project we will burn the food and measure the amount of produced heat energy as a way of estimating the energy that each food can deliver to our body.
Find out about food energy. Read books, magazines or ask professionals who might know in order to learn about the way that food provides energy in our body. Keep track of where you got your information from.
When material burn, they create odor, smoke, vapors and gasses. Sometimes these properties will help us to identify the substance that is burning. In many other cases the smoke, vapors and gasses can be collected, separated and sold as valuable raw material for other industries. Burning either complete or incomplete is the foundation of many industries.
In our body food burns with different chemical reactions and release heat energy. The unit of heat energy is Calorie.
A calorie is a measurement of energy. We tend to associate calories with food, but any sort of energy can be measured in calories. The official definition of a calorie is the amount of energy needed to raise the temperature of a gram of water by 1 degree C. A kilocalorie is 1,000 calories. Just to make life confusing, the “calorie” that you see on packages of food is really a “kilocalorie” in the scientific sense.
It makes sense that food contains energy, because most foods burn. For example, if you have ever roasted marshmallows, you probably know that marshmallows burn. What’s burning in that case is the sugar in the marshmallow. Fat burns too — you know that if you have ever seen a grease fire. Your body “burns” fats, carbohydrates and proteins — not with flames, but with more controlled chemical reactions that release the energy in different ways.
Fats, proteins and carbohydrates have characteristic calorie measurements. One gram of fat contains almost 9 calories (kilocalories) of energy. One gram of any carbohydrate contains 4 calories (kilocalories). One gram of protein contains 4 calories (kilocalories) as well. Knowing these values, you can calculate the number of calories in any food as long as you know how many grams of fat, protein and carbohydrates it contains. If you were to take any food, dry it out and burn it, the specified number of calories would be released by the flames.
If you ingest 3,500 extra calories one day (or over the course of several weeks or months), your body will convert the excess energy to body fat and save it for a rainy day. To lose 1 pound of fat, therefore, you have to burn off the 3,500 excess calories. You can do that either by exercising or by restricting your calorie intake.
The USDA estimates that the average man, 5 feet 10 inches tall and weighing 174 pounds, needs 2,900 calories per day (assuming light to moderate activity). The average woman, 5 feet 4 inches tall and weighing 138 pounds, needs 2,200 calories.
In food laboratories a bomb calorimeter is used to measure the food energy.
Bomb calorimeter is a closed system where the food is literally “blown up” and all the heat energy is accounted for. The literature value for the heat content of raw almonds is 28.4 kJ/g, Brazil nuts = 30.1 kJ/g, pecans = 31.6 kJ/g, pistachios = 27.6 kJ/g, black walnuts = 28.6 kJ/g and peanuts = 23.6 kJ/g.
In a visit from a rural area and a farm I saw a goat that is eating newspaper. At that time I thought poor goat, does not have food to eat so he is eating newspaper. 25 years later I learned that newspaper is a food for goat and many other animals such as deer. Paper, wood and cotton are all cellulose. Cellulose is a large polymer of sugar. Human stomach does not have any enzyme to break the cellulose and convert it to plain sugar (glucose). However some animals including goats have enzymes that can digest cellulose.
If we eat paper, we do not get any energy from that, but if we burn it we will get some heat. This example shows that not always we can burn material to calculate their food calorie for human. Also the amount of food calorie depends on the rate of digestion. It may happen that only a small portion of the food that we eat will be converted to energy. So the results of our food burning experiment may be used as food energy if a food can be fully digested and absorbed.
In this experiment, you will burn several types of nuts and snack foods in order to determine their heat content per gram.
Why do I perform my experiments on nuts and snack? Can I test meat, vegetables and fruits?
Nuts and snack are usually dry and are ready to be burned. Other foods can be tested too, but you first need to dry them up.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The independent variable is the type of food and snack that we test. The dependent variable is the amount of released heat per gram of food sample.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
I think that food items with higher fat content produce more heat. So peanut will produce more heat than fat free potato chips.
Most snack foods specially peanut and walnut will burn producing an impressive amount of flame for a long time. The flame can be used to heat up water and count the calories contained in the food. This procedure is designed to measure the heat contents of peanut, however you may repeat that with any other dry food with slight changes based on the shape and the size of the food sample. The setup or device that you will construct for this experiment is a simple calorimeter.
- Setup an empty soda can on a stand.
For example you may use a bottle opener, punch two triangular holes at the top of the soda can and slide a stirring rod through the holes. You may then place the soda can on the ring clamp over the nut/food burner, using the stirring rod to support the can.
- Mass out 100 grams of water in the soda can.
- Measure the initial temperature of the water.
- Mass out approximately 2-3 grams of the nut/food sample.
- Construct a nut/food burner. Bend the large paper clip as shown to make a peanut holder. Use tape to mount the paper clip in the center of the pie pan. The pie pan is necessary because the burning peanut may fall off the holder or drip flaming fat drops. Pierce and secure a peanut on the peanut holder.
- Position the can approximately 3-4 cm above the nut/food.
- Ignite the nut with a match, and allow it to heat the water inside the can, while stirring continuously.
After the nut/food burns completely, record the final temperature of the water, and determine the actual mass of nut/food that has burned. Repeat the procedure, using a different type of nut/food sample.
How you hang the can, it’s entirely up to you and depends on material that you can find and use. Just make sure that your setup is secure and does not pose any hazard.
To make sure that your sample will fully burn, start it’s flame from below. After the sample is burned you may optionally weight the remains and deduct it from the original weight of your sample. In this way you calculate the weight of the portion that actually burned.
NEED A CONTROL?: Scientific method requires having a control group or control experiment to make sure that no external factor has affected our results. In this experiment control can be another can of water set aside. By measuring the temperature of this can before and after your experiment, you will show that changes in the temperature are not caused by an external factor.
HAZARDS: The obvious concern is for burns. Make sure you are not allergic to the nuts and/or their burning. Check with your parents before proceeding. Some nuts may be substituted or omitted. Black soot will form on the bottom of the can which may stain clothing.
DISPOSAL: Discard the ash in the waste basket. Recycle the soda cans.
Materials and Equipment:
- one soda can
- centigram balance
- stirring rod
- ring stand and iron ring
- paper clip
- thermometer, range to 110 degrees C (See samples)
- pie pan or aluminum foil
- 2-3g sample of each type of nut or snack food, such as chips or marshmallows
Results of Experiment (Observation):
Using your data for the mass of the water, the mass of the nut that actually burned, and the initial and final temperatures of the water, calculate the heat released per gram of nut/food burned. Enter the results of your experiments in a table like this:
|Food item||food mass||Water mass||initial temperature||Final temperature||Food energy|
1. How many calories of heat were passed to the water during the burning of each food? Of the two which had the most stored energy?
2. What organic material was the main source of stored energy in each food?
3. Of the organic compounds found in living organisms, which one has the most energy per gram.
4. Did all the heat from the foods that you tested go directly into the water? If not where did it go?
7. With this additional data, was this an accurate measurement of the caloric capacity of the foods that you tested?
8. What type of experimental set up could be developed to get a more accurate measurement?
- Calculate the change in temperature of the water.
- Calculate the heat that was released by the food and absorbed by the water in calories and in joules.
Heat absorbed by water in calories= (mass of water in grams) x (temperature change in Celsius degrees)
- Calculate the calories released per gram of nut/food that burned.
Food energy in calories = Heat absorbed by water ÷ food that burned (in grams)
- To calculate the food energy in Joules you can multiply calories by 4.18.
(NOTE: 1 calorie(c) = 4.18 J)
- Examine the “Nutritional Value Information” found on the package of one of the food samples. Note that 1 Food Calorie(C) is equivalent to 4.184 kJ of heat energy. Use this information to determine the “accepted value” for the heat content per gram of snack food. What is the percent error for your experiment?
- Explain how can you improve the accuracy of this experiment?
- Compare the heat content of the various types of food tested. Use the nutritional information on the side of their packages to determine how much fat and carbohydrates each type of food has. Is there any correlation between these two values?
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Following is a sample of what you may write in the summery of results:
The value for kilojoules per gram of nut/food determined by this procedure is generally much lower than the value in the literature, but they are proportionately lower for each type of nut/food tested. You can try to make a more efficient calorimeter.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
If you need to verify your results, you may click here to see a table of food calories for snack foods. Just remember that 1 Calorie equals 1000 calories. (Food Calorie starts with capital C and equals 1000 calories)
You may also click here to see a table of food calories for seeds and nuts.
Visit your local library and find books related to food chemistry and and nutrition.
Following are some sample references:
John Grossman, “How Many Calories Are There In A 230-Calorie Dinner?”, Hippocrates, Sept/Oct 1987 (5).
Submitted by Justin Field Chemistry Institute 1988 with modifications by Mark Case, CHEM 6 Team Binder 1995.