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Topics: Energy, Temperature, Thermodynamics Pages: 2 (256 words) Published: March 28, 2011
Medical Cold Packs- Thermochemistry Experiment 2.1

Purpose:
To use calorimetry to determine the enthalpy of solution of an unknown salt, and then to use that value to identify the salt in the medical cold pack.

Materials:
See handout

Procedure:
1. Acquire two styrofoam cups, and cut the top off one of them. 2. Add 80mL of water and record it's initial temperature. 3. Place 10g of salt into the water and put second on top, creating a seal. 4. Record the temperature of the solution after two minutes. 5. Calculate the change in temperature per mole of solid.

Observations:
Salt| Mass (g)| Initial Temp. (˚C)| Final Temp. (˚C)| Change in Temp. (˚C)| KNO3 | 5g| 22˚| 19˚| 3˚|
NH4NO3| 10g| 11˚| 4˚| 7˚|
NaC2H3O3H2O| 10g| 14˚| 11˚| 3˚|

Calculations: See attached sheet

Evaluation/Sources of Error:
a) see attached sheet
b) Sources of error:
* Heat transferred to surrounding environment, which cannot be calculated. * Not all of the salt was reacted with the water; not all added * Temperature reading on thermometer was not very precise

c) If some heat were transferred to the air or Styrofoam cups, the calculated enthalpy would be too low as the energy change in the system would not include the transfer of heat to the Styrofoam.

d) If some salt was accidentally spilled, the calculated enthalpy would be too high as the mass of the salt is need to calculate the enthalpy, yet that mass was not present, and therefore could not affect the temperature as the full amount would.
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