Lab: Calorimetry

Goal: To determine the heat capacity of a simple calorimeter.

Materials:

• Clean 2 qt pot
• Large beaker or glass jar capable of holding the styrofoam cups (for stability).
• Two styrofoam cups, same size, at least 8 oz (1 cup) capacity. \
• Lid for styrofoam cup. You will need to make this, and it can be aluminum foil, paper, or cut a sheet of styrofoam or cardboard to fit. The lid should have two small holes, one for the thermometer, one for the stirring rod.
• Thermometer, with a range of 0 to 110 °C or 20 to 220 °F [Two if you have them].
• Glass stirring rod. You can substitute a wooden chopstick or skewer. but don't use metal. Why not?

Procedure

1. Nest the two cups together and set them inside the beaker.
2. Place the thermometer in the lid, and position it so that when the lid is on the cup, the thermometer is 2-3 cm above the bottom of the cup, and not touching the sides. You can secure the thermometer in place by wrapping a rubber band around it above and below where it passes through the lid. Remove lid.
3. Measure 100 mL of water and place it in the inner styrofoam cup. This is m_o (original amount of water). If you use a different amount, record the amount.
4. Place the lid on the cup, and wait until the thermometer stops changing. Record the temperature of the water. This is T_o.
5. Using the pot, bring 100-200mL of water to a boil. Measure 30 mL into a small beaker. If you use a different amount, record the amount as m_a (Water added).
6. OPTIONAL: If you have a second thermometer, measure the temperature of the water in the small beaker. Otherwise, assume that it is 100 °C. This is T_a.
7. Add the 30mL of boiling water to the styrofoam cup calorimeter, reseat the lid, and use the stirring rod to stir the water. Try not to hit the thermometer.
8. Watch the thermometer. Record the highest temperature attained. This is T_f.

Data Handling

To calculate the heat capacity of the calorimeter, you determine the change in temperature of the hot water (T_a - T_f = T_af) and the change in temperature of the cold water (T_o - T_f = T_of ).

The calorimeter constant is given by -C(m_o*T_af + m_a*T_of) / T_af. The heat capacity C of water is approximately (-100 cal/g-K).

Report

1. Describe your materials, equipment, an procedures in sufficient detail that your fellow students could repeat your experiment.
2. Report your data. Be sure to indicate the amount of error in your measurements. For example, if you can only measure a mass of 25 gms within 1 gm, your error would be 25 ± 1, or 1/25 = 4%.
3. Present your data in an organized form, preferably in a table, in such a way it is easy to compare results as you repeat trials or vary a specific contributing factor.
4. Show a sample calculation, if you have calculated values.
5. If you did a series of experiments, varying something by increasing or decreasing a factor, try to plot your data (y-axis) as a function of the factor (x-axis).
6. You may use a spreadsheet to calculate your information and create your table.
7. Summarize your results.
8. Draw conclusions about what is happening.
9. Suggest at least one way to improve your experiment.

Post your report to the Lab thread at the Moodle Lab Assignment for this Lab.

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