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A laboratory experiment aimed at investigating the freezing and melting behavior of water. Students will collect temperature data using technology, analyze the data to determine the freezing and melting points, and compare the results. The experiment follows standard safety procedures and includes the use of a Vernier LabPro interface, TI Graphing Calculator, and Vernier DataMate program, among other materials.
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The cooling and warming behavior of water is investigated. With the use of technology, water temperature data is collected, graphed and analyzed. The freezing and melting points of water are determined and compared.
Hypothesis The freezing and melting points of a substance may be determined by observing the warming and cooling behavior of that substance.
Primary Learning Outcomes At the end of this lesson, students will be able to:
Assessed GPS
SCSh2. Students will use standard safety practices for all classroom laboratory and field investigations. a. Follow correct procedures for use of scientific apparatus.
SCSh3. Students will identify and investigate problems scientifically. c. Collect, organize and record appropriate data. d. Graphically compare and analyze data points and/or summary statistics. e. Develop reasonable conclusions based on data collected. f. Evaluate whether conclusions are reasonable by reviewing the process and checking against other available information.
SCSh4. Students will use tools and instruments for observing, measuring, and manipulating scientific equipment and materials. a. Develop and use systematic procedures for recording and organizing information. b. Use technology to produce tables and graphs. c. Use technology to develop, test, and revise experimental or mathematical models.
SCSh5. Students will demonstrate the computation and estimation skills necessary for analyzing data and developing reasonable scientific explanations. b. Consider possible effects of measurement errors on calculations. c. Recognize the relationship between accuracy and precision. d. Express appropriate numbers of significant figures for calculated data, using scientific notation where appropriate.
SC6. Students will understand the effects motion of atoms and molecules in chemical and physical processes. a. Compare and contrast atomic/molecular motion in solids, liquids, gases, and plasmas. b. Collect data and calculate the amount of heat given off or taken in by chemical or physical processes. c. Analyzing (both conceptually and quantitatively) flow of energy during change of state (phase).
Duration 90 minutes
Materials and Equipment 400-mL beaker 10-mL graduated cylinder test tube salt ice water ring stand utility clamp
Technology Connection Vernier LabPro interface TI Graphing Calculator Vernier DataMate program Vernier Temperature Probe
Procedures
Step 1: Introduction/Motivation, 20 minutes If necessary, prep temperature probes, including calibration as outlined in the manual accompanying temperature probes. Put some ice cubes in a beaker containing warm water for the students to see. Elicit responses as to what is “really” happening (emphasis on the molecular level). Lead a discussion as to what happens to molecules of H 2 O in a given phase when in contact with other H 2 O molecules in a different phase (e.g., water vapor and ice, water and water vapor, water and ice). Molecules of a substance exhibit increasing disorder as phase changes from solid to liquid to gas. As disorder increases, so does the frequency of molecules of a substance colliding with each other and with their surroundings. Thus, the kinetic energy of molecules in a substance increases as disorder increases. Conversely, the potential energy of the molecules in a substance increases as the tendency of molecules to become disordered increases. Irrespective of the method of temperature observation (e.g., thermometer, temperature probe attached to electronic data collection device, etc.), graphs of temperature vs. time for water that is warming and for water that is cooling will have a characteristic appearance:
Show students what the setup is supposed to look like, including initialization and preparation of the probe, LabPro device, and calculator. Refer to the student activity handout for visual. Have students look over the student activity handout to anticipate the sequence of data entry and button combinations on the TI calculators. Ask if there are any questions about the procedure ( minutes max).
Step 2: Activity, 50 minutes Students will break up into groups and conduct activity “Freezing and Melting of Water” as outlined in student activity handout. Recommendations:
Step 3: Review, 20 minutes Gather students as a class and discuss results, answers to the review questions given at the end of the student handout, and any problems or questions with the procedure. A brief mention should be made of the concepts of precision (repeatability of results) and accuracy (proximity to the “true” value) if there is an issue with the calculated freezing and melting points of water not being 32˚F/0˚C.
Assessment Completed student worksheets will be collected and graded. Student understanding of activity components may be assessed by unit examination. Student affect and work ethic may be assessed by affect/ethic rubric.
References Holmquist, D.D., Randall, J. & Volz, D. (2000). Chemistry with Calculators. pp. 1-1 – 1-T3. Vernier Software & Technology: Beaverton, Oregon.
Freezing temperature, the temperature at which a substance turns from liquid to solid, and melting temperature, the temperature at which a substance turns from a solid to a liquid, are characteristic physical properties. In this experiment, the cooling and warming behavior of a familiar substance, water, will be investigated. By examining graphs of the data, the freezing and melting temperatures of water will be determined and compared.
Figure 1
LabPro or CBL 2 interface 400-mL beaker TI Graphing Calculator 10-mL graduated cylinder DataMate program test tube Temperature Probe salt ring stand ice utility clamp water
Part I Freezing
Name_____________________________________________
Freezing temperature of water °C Melting temperature of water °C