Experiment #1 / Unit 6

Enthalpy of Fusion for Dihydrogen Monoxide -

a Study of Hydrogen Bonds

Introduction:

The heat of fusion of a substance represents the amount of heat energy which is absorbed as the substance changes from a solid to a liquid. In this experiment, we will use a melting ice cube to determine the Hfus for water. Of course its melting point & enthalpy of fusion is determined by how well the molecules stick together……so we will be measuring the stickiness & energy involved in forming & breaking hydrogen bonds.

Procedure:

Day 1

  1. Measure the mass of an empty styrofoam cup.
  2. Fill the cup about 2/3 full with water and mass the cup and water.
  3. Suspend a temperature probe in the center using materials (Parafilm, cardboard, wood splints, tape, etc.) for stabilizing the probe in the center of the cup for freezing. Label your cup.
  1. Start up Logger Pro. The default settings for remote data collection are not good; 180 total seconds at one reading per second. Set up your temperature sensor to have a sampling rate of one reading per 15s for overnight.
  2. Run a short trial run of remote data collection. Select the “Experiment” menu, “Remote", "Remote Setup". Hold the probe in your hand to get a change in temperature. Reconnect to the computer and see if you get data. Now set up for the real trial.
  3. Carry the cup with probe, interface, and AC adapter into the back stockroom.
  4. Plug the AC adapter into the power strip.
  1. Disconnect the interface box from the computer
  2. Place your cup in the freezer. Using a beaker will stabilize it and keep it from tipping over on the shelf. The interface box can sit on the top of the freezer.
  3. Press the start button and make sure that it begins logging (you will see the light blinking at the rate you set it to collect data).
  4. Close the freezer slowly so the “popsicles” do not fall over.

Day 2

  1. Set up a large styrofoam container to act as a calorimeter for the large "popsicle" we created overnight.When filling the calorimeter, use and empty Styrofoam cup to displace the volume of the popsicle so you will have room for that additional water without overflowing. Fill the calorimeterwith warm water (50-75 *C).
  2. Measure the mass of the calorimeter and the water. Obtain a second temperature sensor to monitor the temperature of the warm water in the calorimeter every 15s.
  1. Retrieve your popsicle by reconnectingthe interface to your computer while it is still plugged into power. The hardware will be recognized and your data will be imported. Save this data.
  2. Add a second temperature probe. Open a new experiment. You are now running two temperature probes - the original in the ice and a new one in the warm water calorimeter. Be careful not to pull the probe out of the ice cube.
  3. Once you have both probes logging, tear the styrofoam cup from around the “popsicle” and place it in the warm water.
  4. After the “popsicle” has completed melting and the temperature of the warm water and the melted ice water have equilibrated, stop the data logging.
  5. Measure the mass of the calorimeter, water, and melted ice water.

Data:

  • mass of empty styrofoam cup (for popsicle)
  • mass of cup and water
  • mass of empty calorimeter container
  • mass of calorimeter container and warm water
  • mass of calorimeter, calorimeter water, & popsicle water
  • graph of temperature readings for water in popsicle during cooling
  • graph of temperature readings for water in popsicle during warming
  • graph of temperature readings for warm water

Calculations and Questions:

1. Draw labeled heating and cooling curves to illustrate the heat transfer that took place in the calorimeter.

2. Determine the change in temperature for the warm water after adding the ice cube.

3. Determine the change in temperature for the warming ice cube.

4. Find the change in temperature for the melted ice (cold liquid).

5. Calculate the heat of fusion (Hfus) for water. Write all steps for the heat transfer beginning with heat lost = - (heat gained). Label each portion of the heat.

6. Calculate your percent error. The accepted value for the heat of fusion of water is +80. cal/g.

7. Calculate the molar heat of fusion (Kcal/mol) for water using your experimental value.

8.You collide with another player during a game. Your knee is angry & swollen. The trainer provides you a bag of ice. How much heat energy will your knee lose if there are 3.0 pounds of ice (assume the ice arrived at -15.0 *C & finishes at +15.0 *C) in the bag? Also assume that no energy was absorbed by the air & other surroundings.

9. How many Big Macs (591 Kcal) would represent the potential energy needed to melt a 500. ton glacier (at -5.0 *C)?

10. Draw a model that shows the arrangement of water molecules in the glacier. What is the most unusual property of water in the solid state? What forces must be overcome to melt the glacier and allow the water molecules to flow freely from one another?

11. What volume would the glacier occupy? What volume would it occupy after being melted? What percent larger is the glacier in solid form?

Lab Report #6.1:

  • title page
  • abstract
  • procedure
  • data & graphs
  • calculations and questions

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Chemistry II CaryAcademy W.G. Rushin