Chemistry Lab: Heat of Fusion of Ice

CHEMISTRY LAB: HEAT OF FUSION OF ICE (ICELAB.DOC) Name: ______

Date: ______

1. Introduction: The amount of energy required to convert a solid to a liquid, at constant pressure and temperature, is called the heat of fusion of the substance. The amount of energy required to completely change one mole of a solid, at its melting point, into a liquid is called the molar heat of fusion.

2. Overview: In this experiment, the molar heat of fusion of ice will be determined. The equation for the change of state involved is:

1 mol H O (s) + __?__ kJ ---> 1 mol H O (l) 2 2

The ice will be melted by placing it in a known volume of hot water contained in a foam plastic cup. The system will be left undisturbed until all the ice has melted. The amount of heat lost by the hot water can be calculated using this equation:

(heat lost) = (mass) x (specific heat capacity) x (change in temperature)

The heat lost by the water will be absorbed by the melting ice. The volume of ice that melts can be determined by measuring the volume of the water in the cup before the ice is added and after the ice has melted.

(volume of melted ice) = (final volume of water) - (initial volume of water)

The mass of melted ice can be calculated from its volume and density.

(mass) = (density) x (volume)

If the mass of the ice melted and the heat absorbed by the ice are known, the heat required to melt one mole of ice can be calculated.

(heat absorbed by ice) x (molar mass of ice) molar heat of fusion of ice = ______(mass of ice melted)

3. Safety: Goggles must be worn whenever the burner is in use. Rinse your hands at the end of the lab period and whenever you suspect you have contacted any unusual substance. Make sure your area is clean before you start and when you leave. When the graduated cylinder is not in use, lay it down gently so no one will knock it over and chip the top edge. Guard against letting the thermometer roll into the sink or off the table and break. Leave the little triangular roll-guard on the thermometer and lay it down gently to avoid breakage. Do not return ice to the cooler, and do not eat or drink anything in the lab. Return your goggles to the sterilizer when the lab is over. 4. Equipment:

from lab station: ring stand with medium ring and wire gauze burner, gas hose, and spark lighter 600 ml beaker, 250 ml beaker, and beaker tongs 100 ml graduated cylinder and scoopula

from prep area: foam plastic cup with lid thermometer ice

5. Procedures:

a. Assemble the ring stand in the usual way and begin heating about 300 ml of water in the 600 ml beaker. Use the thermometer to tell when the water has reached about 60 degrees Celsius.

b. Fill the foam cup about halfway with ice, drain off the extra melt water, and place the cup containing the ice into a 250 ml beaker for stability and extra insulation.

c. When the water you're heating reaches 60 degrees, turn off the gas and set the burner out of the way to cool. Using the beaker tongs to handle the hot beaker, preheat the graduated cylinder by pouring about 30 ml of warm water into the cylinder, and tipping the cylinder this way and that, wet the inside surface all over to warm the glass. Pour out the warm water. Repeat with new warm water.

d. Working quickly, pour about 30 ml of new warm water into the pre-warmed graduated cylinder. Measure the volume to the nearest tenth of a milliliter. Insert the thermometer gently and measure the temperature of the water as it stands in the graduated cylinder to the nearest tenth of a degree. Record the volume and temperature.

e. Working quickly, drain the melt water from the ice in the cup, and add the measured hot water in the graduated cylinder to the cup half-full of ice. Stir the ice and water mixture gently but thoroughly until the temperature falls to about 2 degrees. At this point, some unmelted ice should remain, but if it has all melted, add a bit more so that some ice remains unmelted when the temperature is 2 degrees or below. Record the lowest temperature reached by the ice and water mixture.

f. Using the scoopula, quickly remove any unmelted ice from the cup. As you remove the ice, drain as much water as possible back into the cup.

2 g. Carefully pour all the cold water from the cup into the now empty graduated cylinder and record the final volume to the nearest tenth of a milliliter. If you have more than 100 ml of water, you'll have to make two measurements and add them together.

6. Data:

volume of hot water added to ice _____ ml

initial temperature of hot water (in graduated cylinder) _____ C.

final temperature of water and melted ice _____ C.

final volume of water and melted ice _____ ml

7. Calculations:

a. Calculate the change in temperature of the hot water as it cooled from its starting temperature to the final temperature.

T = _____ C.

b. Determine the mass of the water that was added to the ice. [Remember: the density of water is 1 g/ml.]

(volume)  (density) = (mass)

_____ g

c. Calculate the heat lost by the hot water as it cooled. First, calculate it in calories, then convert it to joules, and then kilojoules. [Remember: the specific heat capacity (c) of water is 1 cal/gdeg.]

Q = (m)  (c)  (T)

_____ calories x 4.184 J/cal = _____ J

_____ Joules x 1 kJ/1000 J = _____ kJ _____ kJ

[This amount of heat supposedly all went toward melting the ice.]

d. Calculate the volume of the ice that melted. (How much new water appeared in the cup?)

_____ ml

3 e. Calculate the mass of the ice that melted. [Remember: the density of water is 1 g/ml.]

volume of water x 1 g/ml = mass of water _____ g

f. Calculate the number of moles of ice that melted. Use the atomic masses of oxygen and hydrogen to calculate the number of grams in one mole of H O. 2 [H = 1.00794; O = 15.9994.]

one mole of H O = ______g [This is the molar mass.] 2

mass of ice (g) x (1 mol ice / _____ g ice) = (moles of ice)

_____ mol

g. Use the answers to 7c and 7f above to calculate the molar heat of fusion of ice.

_____ kJ / mol

8. Analysis:

Compare the experimental value you determined to the accepted value of 6.02 kJ/mol.

percent error = {( | accepted - experimental | ) / (accepted)} x 100 %

_____ % error

9. Clean up and return the plastic cup, cup lid, and thermometer to the prep area. Return the goggles to the sterilizer cabinet. When your equipment has cooled, return it to storage. Return to your seat to do the calculations.