Beacon Lesson Plan Library

Melting Ice is Hot Stuff!

Rosemary Wilson
Santa Rosa District Schools

Description

Students will use crude calorimeters to determine the amount of energy required to melt ice and will be able to calculate the Molar Heat of Fusion of Ice.

Objectives

The student knows that change from one phase of matter to another involves a gain or loss of energy.

Materials

- Styrofoam© cups, large and small sizes, approximately seven of each size per class.
- Red Alcohol thermometers, one per lab group, approximately seven per class.
- Plastic cup lids, one for each cup used.
- Triple Beam balances, one per lab group, approximately seven per class.
- Ice, approximately 24 cubes per class.
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Preparations

1. Gather all materials needed to perform the activity.
2. Copy the attached lab activity sheet, one copy per student.
3. Copy the attached rubric, one copy per student, for the grading portion of the activity, making students aware of the guidelines they should use to write their lab reports.
4. Make sure you have red alcohol thermometers for this activity. Do not use mercury thermometers.

Procedures

1. Begin instruction by asking the students to imagine a container of ice cubes. Ask the class for suggestions as to how you could change the solid ‘water’, ice, to liquid ‘water’.
2. After several students have given you suggestions, point out to the class that all the suggestions have mentioned the application of some sort of heat source. Remind the students that changes in states of matter require either energy applied, endothermic, or energy released, exothermic.
3. Give a brief synopsis of the lab activity the students will be accomplishing during “Melting Ice is Hot Stuff!”
4. Explain to the students that in order for them to accomplish the activity with good results and in the time frame allowed, they must work cooperatively together. Explain that they may want to separate the steps of the activity so that each member has specific steps to accomplish. Tell the students they could also determine definite roles for each member in order to work together cooperatively. These roles could include the following:
a. group leader
b. materials gatherer
c. data recorder
d. clean-up
5. After you have explained how the students should work together, explain how the calculations are accomplished. This step should include definite examples of how the Molar Heat of Fusion is calculated using the appropriate formula.
Choose any numbers to illustrate using the following steps:
a. Calculate the number of grams of ice by subtracting the mass of the small Styrofoam© cup from the mass of the cup and ice together.
b. Calculate the number of moles of water, ice, you have by dividing the mass of ice by 18 g (to change the number of grams of ice to moles of water.)
c. Calculate the change of temperature by subtracting the ending temperature of the water from the beginning temperature.
d. Calculate the Molar Heat of Fusion of Ice by dividing the change of temperature by the number of moles.
6. Explain to the students the use of a calorimeter and how they should take every precaution to take the measurements as quickly and accurately as possible. Tell them they should take great care to place all the ice into the inside cup quickly to prevent the ice from melting in the atmosphere ahead of time. Explain that a calorimeter works by having a substance change state of matter deriving the energy needed from the surrounding medium. If the surrounding medium is water in the cup, or metal in a purchased calorimeter, the change in temperature can be noted and used for calculations.
7. After sufficient explanations are given, distribute the lab sheets for the activity, located in the associated files.
8. Assist in the activity by helping the students at the demonstration table where they get their ice. Crush the ice for them, place the chips in a dry paper towel and tell the students to place the ice in their calorimeter set-ups as quickly as possible.
9. After the students have completed the lab activity, have all the students return to their seats so you can explain the process of calculating the Molar Heat of Fusion of ice. Repeat an example using the steps illustrated in step 5 of these procedures.
10. Conduct a practice session with the class using example amounts of ice and data collected regarding temperature changes so they can see how the Molar Heat of Fusion is determined. You may want to allow the students to perform their calculations during this session so they can accomplish their calculations at a time when they can ask questions.
11. Allow for questions from the students regarding their calculations. Tell the students the true value of the Molar Heat of Fusion of Ice. Tell them to compare their results with this result. Explain the many areas for error in this type of experiment:
a. Measurement errors
b. Temperature and pressure of the classroom not at STP.
c. Ice melting prior to actual completion of the calorimeter set-up.
12. Follow this activity with student conferences, if necessary, after the final lab sheets have been submitted, graded, and returned. If necessary, lead the class in a repeat of the method of calculations for Molar Heats of Fusion and Vaporization.

Assessments

Students will be given a lab sheet to accompany this activity. The lab sheet will include the procedure for assembly of the calorimeters (either purchased from a supply house or made using Styrofoam© cups), a chart for recording data, a list of materials, and the process for calculation of the Molar Heat of Fusion of Ice.

Lab sheets will be submitted to the teacher for grading according to the attached rubric.

A related problem and question involving the Molar Heats of Fusion and Vaporization are to be included on the chapter test that covers these topics. Examples of related questions would be:

1. Where does the applied energy go that causes water to boil on a stove considering the fact that the temperature of the water does not change until all the water is vaporized?
Answer; The energy is used to break the bonds of the water molecules holding the molecules together as a liquid so they can become individual gaseous water molecules.

2. What would you expect to happen to the surrounding atmosphere of a freezing unit of water in regard to a temperature change?
Answer; The temperature of surrounding air would increase due to the energy released when the bonds of solid water are formed.

3. What would you expect to happen to the surrounding atmosphere of a melting unit of water in regard to a temperature change?
Answer; The temperature of the surrounding air would decrease due to having to supply the energy needed to break the bonds of the solid form of water allowing only the hydrogen bonds to remain.

4. What is the main reason the Molar Heat of Fusion of water is so much lower in value than the Molar Heat of Vaporization of water?
Answer; The molecules of liquid are held together by strong hydrogen bonds that have to be broken before the molecules of the liquid are allowed to separate.

Extensions

The 'calculations' portion of this activity can be used as a class activity to practice the method of determining the energy change that occurs when water freezes or ice melts. Then, the method of this calculation can be used to show the Molar Heat of Vaporization using an example amount of water that vaporizes or condenses.

Attached Files

Melting Ice is Hot Stuff!     File Extension:  pdf

Rubric for Melting Ice is Hot Stuff!     File Extension:  pdf
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