CHEM 103 Name ________________________________________ Lab Section _______ PRELAB Experiment: Calorimetry This pre-lab must be completed outside of
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CHEM 103 Name ________________________________________ Lab Section _______ PRELAB
Experiment: Calorimetry
This pre-lab must be completed outside of the lab, prior the beginning the start of your
lab section.
1. What is energy? 2. What are some units of energy? 3. Define the calorie? 4. Define heat. 5. Define temperature. 6. What is the difference between heat and temperature? 7. It is recommended that 45% of total caloric intake comes from carbohydrate, 25%
from fat, and 30% from protein. What is the protein caloric intake of a athlete that
daily consumes a 3,000 calorie diet? This page intentionally left blank CHEM 103 EXPERIMENT
CALORIMETRY
Reproduction permitted for educational use provided original
Calorimetry is a technique that is used to determine the heat involved in a chemical
reaction. When determining the heat of combustion of a substance or the caloric
value of foods, the measurements are often made using a bomb calorimeter. In this
device, the weighed sample is placed in a heavy steel container called a bomb and the
atmosphere of the bomb is filled with pure oxygen. The bomb is then placed in a
well insulated container called a calorimeter which has been filled with a measured
amount of water. The sample, in the pure oxygen atmosphere, is ignited by an
electric spark and the heat generated by the burning sample warms the bomb and the
surrounding water. At equilibrium, both the bomb and the water will be at the same
temperature.
Using the law of conservation of energy:
Heat evolved by the reaction = Heat absorbed by the water +
Heat absorbed by the bomb
or, in
equation
form: qreaction = -(qwater + qbomb ) (where q is the symbol for heat) The qreaction has a negative value because the combustion reaction is exothermic
(i.e., it releases energy to the surroundings). The qwater and the qbomb are
calculated from the temperature change of the water and the bomb and the specific
heat of the water and the bomb. The total gives the heat of combustion of the sample
that was used.
In this experiment, the energy of a cheeto will be determined using a simplified set-up.
The cheeto will be burned in air, instead of pure oxygen. Instead of a heavy metal
bomb, a metal can, such as an aluminum soft drink can. small juice or soup can is
used. To eliminate the determination of the specific heat of the metal can (the heated
needed to heat the metal that composes the can), the experimental conditions are
modified to maintain a constant temperature of the can by filling it with a large quantity of ice. This will maintain a temperature of 0ºC, as long as all the ice does not
melt. The heat evolved by the burning cheeto will melt some of the ice and the
amount of liquid water formed will be measured to give the heat of combustion of the
sample.
After determining the energy of a cheeto, (or other type of snack food) the procedure
will be repeated using other snack foods.
1. MATERIALS NEEDED: a metal can (a small juice can, soup can, or soft drink
can) with the top removed heavy wire stand to hold the
cheeto. This can be constructed from an extra large paper
clip (see photo on right) 150ºC thermometer graduated cylinder, 100-mL or 250-mL tongs or forceps funnel cheetos or nuts such as peanuts, almonds, cashews,
pecans, walnuts and snack foods such as cheese curls,
potato chips. 2. SAFETY PRECAUTIONS:
Wear safety goggles or glasses at all times in the laboratory. CAUTION –
HEALTH HAZARD: This procedure involves burning nuts. If you are allergic to
nuts, or have any severe food allergies, inform your instructor immediately so
that you may be excused from this experiment. Do not stay in the laboratory.
There are no safety hazards with any of the materials used in this experiment.
The metal stand holding the sample will get hot during the reaction. Handle it
using tongs or forceps.
Do not eat any of the foods used in this experiment. It is assumed that they
may be contaminated with laboratory chemicals.
3. DISPOSAL:
There are no disposal problems with materials in this experiment. Burnt
cheetos, or other snack food, can be disposed of in the trash. Ice and water
should be placed in sink.
4. EXPERIMENTAL PROCEDURE:
Obtain a metal can. If necessary, wipe any carbon deposits off the bottom of the
can using a paper towel. Set up the apparatus as shown in Figure 1. Use a large adjustable clamp to
hold the metal can. Place a metal stand for holding the cheeto on the base of
the ring stand. Loosen the clamp and move the metal can off to the side of the
apparatus. Figure 1. Apparatus for determination of the energy of a peanut
Select a cheeto (or nut), weigh it, and record its mass. Add ice to the can so it
is at least half-filled. Place the cheeto (or other nut used) on the stand and light
it using a match or a burner. Move the can over the burning cheeto and
position it so that the top of the flame just touches the bottom of the can.
Allow the cheeto to burn completely. If the flame goes out and the cheeto is
not completely burned, relight the cheeto. Remember to move the can away
from over the cheeto when relighting it.
After the cheeto has burned out, using the clamp holding the can as a handle,
carefully pour the liquid water (but no ice) from the can into the graduated
cylinder. Placing a funnel on top of the graduated cylinder will prevent any
solid ice from falling into the cylinder. Determine the volume of the water and
record it in your notebook. If desired, you may also measure and record the
temperature of the water.
After the cheeto, or other food material, is burned, some charcoal remains.
Carefully transfer the remaining material to a preweighed piece of weighing
paper, or a weighing dish, and weigh it. Determine the mass of the remaining
material. The mass of cheeto, or food, burned is equal to the initial mass of the
cheeto, or other food, minus the mass of the remaining material.
Repeat the procedure with another cheeto (or the same kind of nut previously
used). How do your results compare with the caloric values on the label of the
food container?
Select different kind of nut than you used for the first two trials, or a sample of
another food material (such as corn or cheese curls, potato chips, or tortilla
chips) supplied by your instructor. Repeat the procedure twice more using the
food sample.
5. CALCULATIONS: In this experiment, heat is measured in calories. One calorie is the quantity
of heat needed to raise the temperature of one gram of water by 1ºC. Due to
the excess of ice in the metal can, the temperature of the system should
remain constant at 0ºC, thus we are melting ice into liquid water at a constant
temperature. The heat needed to melt one g of ice to water at 0ºC is known as
the heat of fusion and has a value of 80 cal/g for water.
The density of water is 1.0 g/cm3, so it is assumed that the volume of water in
mL will be equal to the mass of the water in g.
1 mL H2O = 1 g H2O
The heat produced by the burning cheeto is calculated by the equation:
qcheeto = mwater x 80 cal/g
where: qcheeto = heat produced by the cheeto in calories
mwater = mass of the water in g (this is equal to the volume
of the melted ice in mL)
80 cal/g = the heat of fusion of ice (the heat needed to melt
one gram of ice)
The heat, in calories, generated by a one gram sample of the cheeto is
calculated by the equation: q= q cheeto
mcheeto where:
q = heat generated per gram of sample in
calories
qcheeto = heat produced by the burning cheeto in calories
mcheeto = mass of the cheeto that burned in gram
Calculate the nutritional Calories ( C a l ) or kilocalories (kcal) available from the
cheetos (or other nuts) you used. To calculate kilocalories, divide the heat
generated by 1 gram of sample by 1000. kilocalories= q∗kcal
1000 cal
whereq = heat generated per gram of sample in calories
To calculate &quot;Calories&quot; (kilocalories) per gram (from label) Calories per serving ¿ ¿ Serving ¿ g
Calories per gram=¿
Note:
Cal = kcal = 1000 cal DATA AND RESULTS
Course/Section
Name Partner’s Name (If applicable) Procedure 1. Energy of a
Cheeto Date Trial 1 Trial 2 Mass of cheeto (mi) g g Mass of remaining material after
burning (mf) g g Mass of cheeto that
burned (m) g g Volume of liquid
water (Vwater) mL mL Mass of liquid water (see
calculations section) (mwater) g g cal cal cal/g cal/g kcal/g kcal/g Heat produced by cheeto ( q cheeto ¿
Heat produced by 1 gram of cheeto Kilocalories of heat from 1
gram of cheeto
Percent error
Serving size (from label) g &quot;Calories&quot; per serving size
(from label) &quot;Cal&quot; &quot;Calories&quot; per gram
(from label) Percent error Cal/g % % “Calories” from fat (from label) “Cal”
Mass of fat in serving (from label) g “Calories” from fat per gram of fat Cal/g fat Show your calculations in the space below: QUESTIONS:
1. Why is it necessary to maintain a large excess of ice in the metal can? 2. What errors did you encounter in this procedure and how did they affect the results (i.e., a large effect or a small effect)? 3. How does your value for the caloric energy of a cheeto (or other food) compare to the label information? 4. How did the “calories per gram of fat” compare to the calories from all of the substances in the cheeto? Does the type of substance effect the amount of energy
given off when burned?

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