Heat of Fusion

  During melting, heat is absorbed by the melting solid. In this experiment, you will determine how much heat is needed to melt 1 g of ice. Heat has units of joules (J). The heat used to melt the ice will come from the cooling of warm water and will be measured with a calorimeter. A calorimeter is an insulated container fitted with a device for measuring temperature.

OBJECTIVE:  Determine the heat of fusion of ice (in J/g)

 PROCEDURE:

  1.       Use a balance to measure the mass of the calorimeter. Record this mass in your data table. Using the large flask, obtain some hot water from the hot water faucet at the teacher’s desk and mix with tap water until the temperature of the water is about 30 to 35 °C.

 2.        Use a 100-mL graduated cylinder to measure out 100.0 mL of this water into the calorimeter. Measure the mass of the calorimeter and the 100.0 mL of warm water. Record this value in the data table.

 3.        Place the thermometer into the warm water inside the cup to warm the instrument to the temperature of the water. The thermometer must be in the warm water for at least 15 seconds before ice is added.

  4.      Obtain several pieces of ice out of the cooler.  Drain the ice cubes while allowing them to still have a wet surface.  Add the ice cubes to the warm water.

 5.        Gently stir the contents of the cup as the ice melts. The temperature will stop dropping and level off when the ice has all melted. End your data collection when the temperature stops dropping.

 6.        Measure and record the mass of the calorimeter and water (original water + ice melt).

 DATA

mass of calorimeter                                 ______ g
mass of calorimeter and warm water        ______ g
mass of warm water                               _______g
mass of calorimeter and all water/ice      ______ g
mass of ice added                                  _______g

initial water temperature (maximum)       _______°C                                 
final water temperature (minimum)          _______°C

PROCESSING THE DATA

1. Calculate the change in water temperature, Dt (t_max – t_min).

2.  Calculate the heat (in J) lost by the water melting the ice using the equation

 Q  = m • Δt • 4.185 J/g°C

 where Q = heat (in joules), m = mass of warm water (in g), and Δt = change in temperature (in °C)

 

 3. Calculate the heat needed to melt 1 g of ice (J/g).

 

4.  An accepted value for the heat of fusion of ice is 334 J/g. Calculate your percent error:

 

 

 5.  What assumption did we make about heat lost by the water in the calorimeter as compared to heat gained by the melting ice?

 

 

 

EXTENSION

 Design an experiment to find out if an ice cube taken from a freezer and immediately placed into a calorimeter needs the same amount of energy per gram for melting as does an ice cube that has been outside the freezer for ten minutes.