Lab 22: Dystan Medical Supply Company – Cold Packs and Hot

```Lab 22: Dystan Medical Supply Company – Cold Packs and Hot Packs
Julie Tang
Tina Tran
Chemistry 1225-125
March 25, 2014
Introduction
To help the Dystan Medical Supply Company find the production costs of making hot
and cold packs from using ammonia nitrate, calcium chloride, lithium chloride, or potassium
chloride, calorimetry must be performed. This will determine the molar heat of reaction that each
salt will produce after they dissolve in water. This data can be used to see what salt will reach the
desired temperatures for the hot and cold packs along with the least costly amount of chemical.
Performing this experiment will provide us with the most cost efficient salt to use in hot and cold
packs.
This experiment will provide the Dystan Medical Supply Company with more profit by
finding the most cost efficient chemical needed to produce hot and cold packs; it is important
that the production cost per pack is less than \$5.00 for the company to return a profit. If so, the
company will also have the ability to make the product cheaper for consumers and this process
will be both beneficial for the company and its customers.
Calorimetry can determine the molar heat of reaction of each chemical by measuring its
change in temperature from the addition of salt to cool water. To perform calorimetry, a
calorimeter is needed. A calorimeter is a device that contains the reactants while the heat of
reaction is measured. In this lab, a styrofoam cup is used as a calorimeter because it is a
container with good insulated walls and can prevent heat exchange with the environment. In
order to measure heats of reactions, the reactants are enclosed in the calorimeter. The reaction is
then initiated, and the temperature difference before and after the reaction is measured. The
temperature difference allows us to evaluate the heat released in the reaction. For this lab, one
gram of each of the salts will be added to 25mL of distilled water to calculate the mass of salt
needed to reach the desired temperatures of 0oC and 65oC in a 100mL solution. Two trials will be
performed to increase accuracy in the results.
Experimental
Reagents that will be used
A. Ammonium Nitrate NH4NO3
B. Calcium Chloride CaCl2
C. Lithium Chloride LiCl
D. Potassium Chloride KCl
Procedure
First, determine the calorimeter constant. Calibrate the temperature probe by inserting the
probe into ice water and swirling the probe until the temperature is approximately at 0o C. A
styrofoam cup should be nested upon another cup to provide insulation while measuring
temperature changes. Remove the temperature probe. Set the “min” temperature on the Y axis as
15-18oC and the “max” temperature 70-75o. The
X-axis will represent the time in seconds; set this
from 0 (min) to 250 seconds (max). Assemble the
experiment by placing the styrofoam cup on the
magnetic stirrer with 45-50 grams of tap water to
serve as the cool water. Record the exact mass of
this water to three decimal points. Next, the probe
should be secured by a clamp attached to a ring stand. Lower the probe into the cool water until
it is nearly 1 cm from the bottom of the cup, but not touching the magnetic stir bar. Add about 60
mL of water to a clean, dry 150-mL beaker and heat the water 45-60oC above room temperature
to serve as the hot water. Record the mL of warm water and grams of cool water to one decimal
place. Begin recording the thermogram by pressing “Start”, waiting 5-10 seconds before quickly
pouring 50 mL of the hot water into the calorimeter. Enclose it with a lid. When the temperature
remains constant, the solution is at its final temperature and press “Stop”. Repeat this procedure
twice to increase accuracy.
Next, begin performing calorimetry to find the molar enthalpies of the salts. Using the
same calorimeter that was prepared when determining the calorimeter constant, obtain 1 gram of
each salt. Record the exact value of the salt to one decimal point. Prepare 25 mL of distilled
water (recording the exact grams of water) in the styrofoam cup. Be ready to pour all of the salt
into the water. When ready, press start on the Measurenet and wait about 5-10 seconds before
adding the salt to the calorimeter to begin recording dissolution. Observe the temperature
changes and press stop when the temperature begins to stabilize. Perform this procedure twice
for each of the salts to increase accuracy. To determine which salt should be used for either the
cold or hot packs, investigate the temperature changes in the plots retrieved after performing
calorimetry. The exothermic reactions, resulting in a decrease in temperature, show chemicals
used for hot packs, and the endothermic reactions, resulting in an increase in temperature, show
chemicals used for cold packs.
Results
Experimental Data and Calculations
Calorimeter Constant
Trial 1
Trial 2
Average Calorimeter Constant:
Ammonium Nitrate
Trial 1
Trial 2
Average Molar Heat of Dissolution:
Calcium Chloride
Trial 1
Trial 2
Average Molar Heat of Dissolution:
Lithium Chloride
Trial 1
Trial 2
Average Molar Heat of Dissolution:
Potassium Chloride
Trial 1
Trial 2
Average Molar Heat of Dissolution:
Bibliography
Stanton, B., Zhu, L. and Atwood, C. H. (2010). Experiments in General Chemistry: Featuring
MeasureNet: 2nd Edition. Mason, Ohio: Cengage Learning.
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