Bomb Calorimeter
Our body needs calories energy. But eating too many calories and not burning
enough of them off through vigorous activities can lead to weight gain. Most foods and
drinks contain calories. A calorie is a measure of the amount of energy people get from
eating a certain amount of food. Some foods, such as lettuce, contain few calories. For
example a cup of shredded lettuce has less than 10 calories. Other foods, like peanuts,
contain a lot of calories. For example half a cup of peanuts has 427 calories. In Canada,
most processed food products found in grocery stores have nutrition facts labels on their
package. The label describes the components of the food and fat it contains.
Scientist and nutritionists use
calorimetry to calculate the calorie
content in the food.
A bomb
calorimeter is used to determine the
energy content (calorie) of the food.
In food calorimetry, food is
electrically ignited and burnt in a
bomb calorimeter. The heat that is
liberated is transferred to the water in
the calorimeter, which causes the
temperature of the water to rise. The
entire apparatus is insulated from the
surroundings (the air outside the bomb
calorimeter) and the water is stirred to
ensure precise results. The energy
content of the food is can be
determined by the following equation:
Fig. 1: A bomb calorimeter
EH  mW cW tW
where mW is the mass of the water in the calorimeter, cW is the specific heat capacity of
water (4.2 × 10 J/kg°C), and ∆tW is the temperature change of the water in the calorimeter.
Specific Heat Capacity (Bomb Calorimeter) Lab
Purpose:
To measure the heat capacity of different foods by using the law of conservation of heat
energy.
Equipment:
1 bomb calorimeter
30g of powdered chips
30g of powdered cheesepuffs
30 g of hot chocolate powder
30g of powdered peanuts
30g of milk powder
Procedure:
01)
Use the data table provided to record data.
02)
With teachers assistance, set up the lab equipment.
03)
Fill the bucket of the bomb calorimeter with water, record the amount (mass)
and the initial temperature of the water that is inside.
04)
Put the first food sample in the crucible of the bomb calorimeter and record
the mass of the food sample.
05)
With teachers’ guidance, ensure the calorimeter is completely sealed and
insulated.
06)
Turn on the ignition (this allows to food sample to be burnt) and the stirrer to
ensure the water has an even temperature throughout.
07)
Allow the water temperature to rise. When the water temperature stabilizes,
record the final water temperature.
08)
Repeat step 1 to 7 for other food sample with guided practice and
independently
Analysis:
Use the principle of heat exchange to calculate the specific heat capacity of each food
sample ( EH  mW cW tW ). Remember the heat gained by the water is the food calorie
content.
Discussions:
01)
Look up food calorie from the food labels on the package and list them in a
chart with labels, including their units.
02)
Compare the value that you determined in the lab with the accepted values
that you found in Question 1 above. Did your value agree with the accepted
value to within your experimental uncertainty?
03)
If your value did not agree with the accepted value, give possible reasons from
your la technique that could explain the difference. Be careful that your
reasons make sense.
Conclusion:
Summarize your experimental results by referring to your original purpose.
Results:
Data Table
Food Sample
Mass of Sample
(kg)
Initial
temperature of
sample (°C)
Initial
temperature of
cool water (°C)
Note: One kilogram calorie (food calorie) is approximately: 4.184kJ
Final
temperature of
water (°C)
Change of
temperature of
water (°C)
Specific heat
capacity of
sample (J/kg°C)
Learning Outcome(s)/Goals:
Students will learn the precise measurement of heat transfer in the process of
calorimetery. In addition, students will learn the operation of a bomb calorimeter, and
develop the skills to use it to determine the calorie content of food. Students should be
able to relate the principle of heat exchange in calorimetry to the law of conservation of
energy.
Expectations:
D2.8 Investigate the relationship between the concepts of conservation of mass and
conservation of energy, and solve problems using the mass-energy equivalence.
D2.9 Conduct an inquiry to determine the specific heat capacity of a single substance
and of two substances when they are mixed together.
Assessment:
- Circulating, observing and discussion with students when they are working on the
calorimetry lab activity (assessment for learning)
- Lab Report (Data Collecting and Analyzing) for their accurate and precise usage
of a bomb calorimeter
- Lab worksheet (Final Calculation) for their application of the Calorimetry
concept.
Learning Plan:
- Teaching modelling the procedure and proper usage of a bomb calorimeter.
- Students practice using the bomb calorimeter with teachers and peers’ guidance.
- Students use the bomb calorimeter independently
- Teaching/Learning strategy: Gradual release
- Authentic lab practice