Calorimetry - Energy in Food
The energy your body needs for living (running, breathing, thinking) comes from the food you eat.
Energy content is the amount of heat produced by the burning of 1 gram of a substance, and is measured in joules per gram (J/g). We are used to read the energy in food in Calories. 1 calorie = 4.18 Joules. Calories, with Capital “C” means KILO calorie. (1000 calories)
1 calorie is defined as the amount of heat that is required to increase the temperature of 1 g of water in 1°C
If we know how many grams of water we heat up, and the change in the temperature it suffers, we can calculate how much heat the water absorbed. That is the same as the heat was released by burning the food. Of course there is heat loss in the process. We will account for it in the analysis questions.
In this lab, we will burn different foods and will calculate the amount of heat released in each experiment using the following formula:
| Q = m(H2O-g) x c(H2O-J/g°C) x Δt(H2O-°C) |
Q = heat energy absorbed by the water,
m = mass of water used (in g)
c= specific heat of water (which is 4.18 J/g°C for water).
Δt= change in temperature (in °C)
PURPOSE OF THE LAB
Which food has the greatest energy content?
MATERIALS
- one soda can
- electronic balance
- stirring rod (to hold the can in place)
- ring stand and iron ring
- paper clip
- watch glass, to collect any burnt substance.
- thermometer
- clamp for the thermometer
- Sample of each type of snack food – almonds, walnuts, marshmallows, etc.
HAZARDS:
- Tell your teacher if you have nut allergies!!
- Black soot will form on the bottom of the can which may stain clothing.calorimetry energy in food
- Goggles will be worn at all times.
PROCEDURE:
- Prepare the lab setup as shown in the diagram. The bottom of your can should be approximately 3-4 cm above the food sample.
- measure the mass of the empty soda can. record your measurement
- measure around 100 cm3 of tap water using a beaker.
- Pour the water in the soda can and measure the mass again. record your measurement
- Calculate the mass of the water in the can by subtracting 4 minus 2
- Make a triangle base with the paper clip, then pierce the food sample with the unbent end of the paper clip.
- Find the initial mass of the food sample and the paper clip. Record the measurement
- Measure the initial temperature of the water. Record this temperature in the table.
- By using a lighter or the bunsen burner, ignite your food sample and place it below the can immediately. Some foods catch fire easier than others. Please be patient. If you have problems, call your teacher.
- Stir the water with the thermometer until the temperature reaches around 60°C. DO NOT OVER HEAT . Record the maximum temperature.
- Find the final mass of your food sample and the paper clip. Record this mass in the table.
- Pour out your water, clean the can from the soot. Put fresh water using the beaker again. Be4 sure that the can is empty before placing the water again.
- Repeat the procedure for more food samples as time allows.
DATA TABLE
| FOOD USED | substance 1 | substance 2 | substance 3 |
| Initial mass of food and holder (mi) | _________________ g | _________________ g | _________________ g |
| Final mass of food and holder (mf) | _________________ g | _________________ g | _________________ g |
| Mass of food burned (mi – mf) | _________________ g | _________________ g | _________________ g |
| Final water temperature (Tf) | ________________ °C | ________________ °C | ________________ °C |
| Initial water temperature (Ti) | ________________ °C | ________________ °C | ________________ °C |
| Temp. change: ΔT (Tf – Ti) | ________________ °C | ________________ °C | ________________ °C |
HEAT ABSORBED BY WATER: Q = m x c x Δt
| |||
HEAT RELEASED BY THE COMBUSTION OF THE BURNT SUBSTANCE
| |||
HEAT RELEASED BY THE COMBUSTION OF 100 g OF THE BURNT SUBSTANCE
|
PROCESSING THE DATA
- Calculate the heat absorbed (Q) from each sample using: Q = (Δt)(m)(c). (The mass of water used was m = AROUND 100 g, and the “c” of water is 4.18 J/g°C.) Show your calculations here and complete then the table with the answers
- Divide the heat absorbed (Q) for each sample by the mass of food burned (in grams) to find the energy content in 1 g of each sample. Complete the data table above
CLASS RESULTS:
| FOOD USED | substance 1 | substance 2 | substance 3 |
Group 1
| _________________ kJ | _________________ kJ | _________________ kJ |
Group 2
| _________________ kJ | _________________ kJ | _________________ kJ |
Group 3
| _________________ kJ | _________________ kJ | _________________ kJ |
Group 4
| _________________ kJ | _________________ kJ | _________________ kJ |
Group 5
| _________________ kJ | _________________ kJ | _________________ kJ |
Average
| _________________ kJ | _________________ kJ | _________________ kJ |
Analysis Questions
- Where did the energy stored in the nuts originally come from?
- During what process was this energy stored in the nut, & where specifically was it stored?
- What simple sugar made by plants is a common source for stored energy?
Which group of macro molecules would a nut contain — carbohydrates, lipids, or protein?
- What is the name for stored energy?
Give some examples of how organisms would use this stored energy.
- In this experiment, discuss what happened to the energy stored in the nut.
Why was the final mass of the nut less than the original mass of the nut?
- Calculate the amount of heat released by a compound if it raised the temperature of 50 g of water from 22°C to 55°C.
Express the answer in calories and Joules. - Why do the calories calculated are less than the ones that read in the packages? Explain your answer.
Your lab report should have the following parts:
- Title
- purpose
- materials
- procedures
- data tables
- calculations
- analysis questions
