Calorimetry Determining the Heat of Fusion of Ice

Document Sample
Calorimetry Determining the Heat of Fusion of Ice Powered By Docstoc
					Calorimetry: Determining the Heat of Fusion of Ice
OBJECTIVE
Using a simple calorimeter, determine the heat of fusion of ice.
INTRODUCTION
When a chemical or physical change takes place heat is given off or absorbed. That is, the change is either exothermic
or endothermic. It is important for chemists to be able to measure this heat. Measurements of this sort are made in a
device called a calorimeter. The technique used in making these measurements is called calorimetry.




In simplest terms, a calorimeter is an insulated container made up of two chambers (see figure above). The outer
chamber contains a known mass of water. In the inner chamber, the experimenter places the materials that are to lose
or gain heat while undergoing a physical or chemical change. The basic principal on which the calorimeter works is that
when two bodies at different temperatures are in contact with one another, heat will flow from the warmer body to the
colder body. Thus, the heat lost by one body will be gained by the other. This exchange of heat of heat will continue until
the two bodies are at the same temperature. In a calorimeter, heat is exchanged between the water and the materials
undergoing change until the temperatures are the same. The experimenter can thus make a direct measurement of the
temperature change of the water. From this information, the heat gained (lost) by the water can be calculated. The
experimenter then uses these data to determine the heat lost (or gained) by the materials undergoing change.
In part 1 of this experiment, you will place the ice directly into a measured amount of water. The heat required to melt
ice will be supplied by the water. By measuring the temperature change (DT) of the water, you can calculate the
quantity of heat exchanged between the water and the ice. Using these experimental data, you will calculate the heat
of fusion of ice. The following relationships will be used in this experiment:
    a. heat lost (or gained) = [original mass] x [specific heat capacity] x [change in temperature of the water]
        In symbols, this word formula becomes: q = m x c x ΔT
    b. heat given off by the water = heat absorbed by the ice
    c. [heat absorbed by the ice]÷[mass of melted ice] = heat of fusion of ice
The specific heat capacity of a substance is the quantity of heat energy needed to raise the temperature of 1 gram of a
substance by 1°C. The specific heat capacity of water is 4.184 J/(g x°C).
MATERIALS
250-mL beaker water wire gauze             hot plate                                   calorimeter
100-mL graduated cylinder                  ring stand
ice                                        thermometer
PROCEDURE
   1. In a 250-mL beaker, heat about 125 mL of water to a temperature in excess of 50°C.
   2.    Immediately, measure precisely 75 mL of this heated water in a graduated cylinder and pour it into a Styrofoam
        cup. Record this volume of water in a data table as V1.
   3. Measure accurately and record the temperature of the water in the Styrofoam cup as T1.
   4. Immediately add 4-5 ice cubes. Make sure there is always ice in the calorimeter throughout the experiment.
   5. Carefully and continuously stir the ice-water mixture with the thermometer. Continuously monitor the
      temperature of the ice-water mixture until the temperature stops dropping. Record this temperature as T2.
   6. As soon as the temperature stops dropping, carefully pour the water into a clean dry beaker without
      transferring any of the remaining ice.
   7. Measure and record the volume the water at the end of the experiment as V2.
DATA AND OBSERVATIONS
                    V1 = __________________ mL                              T1 = _____________ °C
                    V2 = __________________ mL                              T2 = _____________ °C

LAB QUESTIONS

   1. Using the known density of water, find the mass (m1) of the original volume water (V1).

   2. Find the volume of the water produced from the melted ice (V3 = V2 - V1)

   3. Find the mass (m3) of this water (V3) produced from the ice.

   4. Find the change in the temperature of the water (ΔT = T1 – T2).

   5. Find the heat lost by original mass of water (qwater = m x c x ΔT)

   6. Find the heat of fusion of ice (qice/m3)

   7. Calculate % error. (accepted value is 336 J/g)

DISCUSSION AND SYNTHESIS

   1. List possible sources of error in this experiment.

   2. How might the use of a calorimeter as shown in Figure 1 reduce some of these errors?

   3. One source of error is flow of heat between the water in the calorimeter and surroundings. Explain how this
      error is reduced by starting with water at a temperature above room temperature and ending with water at a
      temperature below room temperature?

   4. In what way does calorimetry make use of the law of conservation of energy?

   5. Is the process of melting exothermic or endothermic? Give evidence from the lab to support your answer.