Saltwater Conductivity: Trends of the Periodic Table

Transcription

1 Saltwater Conductivity: Trends of the Periodic Table by Kirk and Jennifer Pepper Louisiana Curriculum Framework Content Strand: Physical Science, Science as Inquiry Grade Level 9-12 Objectives: The students will be able to: 1. Use the CBL to measure conductivity of various salt solutions. 2. Identify conductivity trends on the periodic table. 3. Create a bar graph using Microsoft Excel. Teacher Information Benchmarks: SI-H-A7, SI-H-A1, SI-H-A2, SI-H-A3, SI-H-B3, SI-H-B4, SI-H-B5, PS-H- C2, PS-H-A2 Curriculum Integration: Science: Periodic table, ionization, conductivity Time Frame: 90 minutes Materials: TI-83, CBL, conductivity probe, DIN adapter, link cable, salt solutions Math: graphing Language: Lab report Applications: Trends of the Periodic table Student Groupings: Cooperative groups Possible Obstacles to Student Learning: Time involved in operating the CBL Opportunities for Assessment: Informal: checklist during lab work for group and individual performance/participation Formal: Rubric for lab report to be turned in

2 Lesson Procedure: Saltwater Conductivity: Trends of the Periodic Table If an ionic compound is dissolved in water, it dissociates into ions and the resulting solution will conduct electricity. In this experiment, you will study the conductivity trends of groups 1,2, and 13 as you move across the periodic table and as you move down a particular group on the periodic table. Conductivity is measured in microsiemens (µs). Materials CBL, TI-83+, Conductivity probe, DIN adapter, Link cable, waste beaker, Microsoft Excel 0.1 M of the following solutions: LiCl, NaCl, KCl, MgCl 2, CaCl 2, AlCl 3 PROCEDURE 1. Obtain and wear goggles. 2. Obtain an empty waste beaker and a supply of distilled water to wash the probe between samples 3. Prepare the conductivity probe for data collection. Plug the DIN adapter into channel 1 of the CBL and attach the conductivity probe plug to the DIN adapter Set the selection switch on the amplifier box of the probe to the µs range. Use the link cable to connect the CBL System to the TI-83+ graphing calculator. Firmly press in the cable ends. 4. Be sure the probe is clean and dry before beginning the experiment. 5. Turn on the CBL unit and the calculator. Press APPS on the calculator and select the CHEMBIO program and press ENTER. This will bring you to the MAIN MENU. *Note: If using the TI-83 calculator, press PRGM instead of APPS to access CHEMBIO 6. Set up the calculator and CBL for a conductivity probe and a calibration of 0 to µs. Select SET UP PROBES from the MAIN MENU. Enter 1 as the number of probes. Select CONDUCTIVITY from the SELECT PROBE menu. Enter 1 as the channel number. Select USE STORED from the CALIBRATION menu. Select M MICS from the CONDUCTIVITY menu. 7. Set up the calculator and CBL for data collection. Select COLLECT DATA from the MAIN MENU. Select MONITOR INPUT from the DATA COLLECTION menu. Follow the directions on the calculator screen to allow the system to warm up, then press ENTER. Obtain samples of all 0.1 M salt solutions stated in the materials section. Rinse the conductivity probe with distilled water and blot dry Place the conductivity probe in the LiCl solution and press ENTER to began sampling.

3 When the reading on the CBL stabilizes, record your reading from the calculator in the data table. Rinse the conductivity probe with distilled water and blot dry. Repeat step 11 until all solutions have been tested. Clean up your lab station including all equipment and dispose of the beaker contents as directed by your teacher. PROCESSING THE DATA 1. Write a chemical equation for the dissociation of LiCl, NaCl, KCl, MgCl 2, CaCl 2, and AlCl 3 in water. 2. Using the attached handout on Graphing with Microsoft Excel, create a bar graph showing all 6 sets of data (LiCl, NaCl, KCl, MgCl 2, CaCl 2, and AlCl 3 ). Plot the conductivity in microsiemens on the y-axis, and the solutions (all 6) on the x-axis. 3. Explain the trend in conductivity as you move across the periodic table from group 1 to group Explain the trend in conductivity as you move down a group on a periodic table. HINT: Hydrated ion size Using your data, predict possible conductivity for BeCl 2 and SrCl 2. Explain your answers. Data Table 1: Conductivity of salt solutions Solution Conductivity (µs) LiCl NaCl KCl MgCl 2 CaCl 2 AlCl 3 Attachments Attachment 1. Graphing with Microsoft Excel Attachment 2. Rubric

4 Exploration and Extension 1. Using trigger prompt mode on the CBL, add 1-drop portions of salt solution, measuring conductivity, and entering the total number of drops added-until a total of 8 drops have been added. After all solutions have been tested, select stop and graph from the data collection menu and examine the data points. (See pgs in Chemistry with the CBL book for a more detailed description of the lab. 2. Using Graphical Analysis, plot conductivity vs. volume of all solutions and draw a best-fit linear regression line on each of the plots. Reference:: Holmquist, D., Randall, J., Volz, D.; Chemistry with the CBL. Vernier Software, 1998.

5 Attachment 1. Graphing with Microsoft Excel 1. Open Excel to a new sheet. 2. Type in your solution names in column A, starting in cell A2. (Do not put anything in cell A1) 3. In cell B1, type in Conductivity (microsiemens). 4. Type in your conductivity data in column B starting with cell B2. 5. Click on the Insert menu and select Chart. 6. Select Column from the Chart type and the 1 st graph from the Chart sub-type. Click Next>. 7. Select Columns from the Data Range menu. Click Next>. 8. Select the Titles menu. Type Conductivity of Salt Solutions under Chart title, Salt Solutions under Category (x) axis, and Conductivity (microsiemens) under Value (Y) axis. 9. Select the Axes menu. Check Category (x) axis, Automatic, and Value (Y) axis. 10. Select the Gridlines menu. Check Major gridlines under the Value (Y) axis. 11. Select the Legend menu. Uncheck show legend. 12. Select the Data Labels menu. Check None under Data labels. 13. Select the Data Table menu. Uncheck Show data table. Click Next>. 14. Select As new sheet. Click Finished. 15. You can change the color of the bars or background by left-clicking on the object you want to change the color of and then right-clicking. Select Format Data Point. Select your color, style, weight, and/or fill effect and click OK. 16. To print your graph, Click on the File menu. Select Print and OK.

6 Attachment 2. Lab Report Rubric Section Points Possible Points Earned I. Introduction: Total 5: 1. Cover page 1 2. Name(s) 1 3. Clear title 1 4. Date 1 5. Class period 1 II. Statement of Problem: Total 12: 6. Problem statement 2 7. Background information 3 8. Clearly stated hypothesis 2 9. Support for hypothesis Independent/dependent variables identified 2 III. Experimental Design: Total 3: 11. Easy to follow procedure (listed in steps) 3 IV. Data Collection/Display: Total 11: 12. Clear data tables (appropriate data, title, units, 5 sig. figs., neat) 13. Clear graphs (appropriate type, scale, title, axes 6 labeled, variables on appropriate axis, accurate plot, neat) V. Data Analysis: Total : 14. Accurate answers to questions #quest x Fully supported answers to questions #quest x 2 VI. Conclusion: Total 5: 16. Hypothesis addressed Support for conclusion 4 VII. Other: Total 3: 18. Grammar Neatness 2 Total