Lab Instructions: Heat Properties of Water

Heat capacity and latent heat of vaporization of water.

  1. Weigh the empty plastic beaker (#1) and the Teflon coated stir bar. Fill it up to 3/4 with cold tap water. Weigh again and determine the amount of water in the beaker.

  2. Put the beaker on the magnetic stirrer. Add the thermometer, and the unplugged electric heater (Fig. 1). Set the magnetic stirrer to its highest position and record the temperature.

    Note: Make sure that the heater, the stir bar and the thermometer do not touch each other.

  3. Plug the electric heater in the outlet and start the stop watch. Record the temperature and stop watch time at intervals about every minute.

  4. Watch for the moment that the water starts boiling and record temperature and elapsed time.

  5. Continue to record the temperature as a function of time for another 5 minutes.

  6. Unplug the heater and turn off the magnetic stirrer. Remove the thermometer and the electric heater. Put the heater into a second beaker with the cold water to cool. Use the heat resistant glove and weigh the beaker on the balance. Determine the weight of water remaining in the beaker.

  7. Transfer measured time and temperature data into an Excel spreadsheet. The power of the heating element is given on the element in Watts (W). Calculate the amount of heat in Joules (J) that has been added to the water as a function of time (1 W = 1 J/s). Plot the temperature as a function of amount of added heat.

Questions:

  1. Describe the general shape of the curve: how does temperature change as a function of time, including the 10 minute boiling interval?

  2. Determine the specific heat capacity of water (amount of heat required to increase the temperature of 1 gm of water by 1 degree Celsius) from the data points between the initial water temperature to the temperature just before boiling (100 degree C). Express the heat capacity in calories/gm deg C (1 J equals 0.239 cal).

  3. The heat capacity of water is of the order of 1 calorie/g deg C. Your result should be in that ballpark. Can you think of any reasons, why your experiment may not reflect the precise value of the heat capacity?

  4. Determine the quantity of water lost by vaporization and the amount of heat added after the water has reached 100 C. How much heat is needed to convert 1 gm of liquid water to 1 gm of water vapor (latent heat of vaporization)?

  5. Imagine you have a certain quantity of water. Which is the more effective way to transport heat, as sensible heat or as latent heat?

  6. How would you perform an experiment to determine the latent heat of fusion? (Maybe we will add it to the lab next year.)

Lab Report Instructions

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last updated 2/15/01
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