Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Experiment 1 Using Pennies and Good Sense Adapted from “An Experiment in Thinking Scientifically” D.J. Sardella, J. Chem. Ed. 69, 1992, 933 Purpose: This is a general introduction to the collection of laboratory data, the errors associated with data collection, the use of statistical techniques to quantify the uncertainty in the collected values, and the use of the laboratory’s data entry and retrieval system to access a spreadsheet program to calculate and present experimental results, The objective of the experiment is to determine the year when the US mint changed the chemical composition of the penny from just copper to a copper/zinc mixture. Background: Faced with budget deficits and rising costs for materials, the US mint decided in the early 1980’s that significant cost savings could be achieved by the Federal government through the elimination of the simple Lincoln-head penny. Pennies had been, to that point in history, minted by striking a single blank of pure copper metal in die sets at the various United States Mints, by the Bureau of Printing and Engraving. The high cost to the government for copper, and other “strategic metals”, for coinage purposes, nearly spelled the end for the simple penny. It simply cost more to make the penny that it was worth. However, merchants and the general public voiced considerable opposition to the phasing out of the penny, and a new formulation of metal blank (copper/zinc mixture) saved the one-cent piece from extinction The mass of the “new” penny was, of course, different that it had been given that it was a new formulation from what had previously been used. In this simple experiment, it is possible to independently determine both the year in which the “new” penny appeared, and the consequences of changing the metal composition on the average masses of the pennies thus produced. The Experiment: Each student will be assigned a mint year by the lab instructor. A vial containing pennies from the mint year will be available on the instructor’s bench at the front of the lab. The mass of each penny for the mine year will be determined using an electronic balance. The mint year and penny masses will entered into the laboratory data retrieval system. After class, the spreadsheet will be retrieved and modified to compute the following for each mint year: The sum of the masses for each set of penny masses. The average (mean) mass of each set of penny masses. The standard deviation of each set of penny masses. Charts depicting the relationship between Mint Year and Mean Mass and Standard Deviation will be created. The student is referred to Appendix C for an overview of data precision and accuracy, and Appendix D for an overview of statistical analysis. All data reported in the laboratory report must conform to accepted standards for reporting data to applicable precision and significant figures. Pre-Lab Report & Notebook: Download from the department data base to your hard drive or flash drive a copy of the lab report template and the data summary table for the Pennies experiment: http://chem.gmu.edu/templates Print the “Summary Results Table” for the Penny experiment. Prepare the Pre-lab report according to instructor’s instructions. Materials and Equipment: Materials Set of Pennies Equipment Electronic Balance Calculator Procedure: 1. Using one of the digital balances located around the lab obtain the mass in grams to the nearest 0.001g for no more than ten of the pennies you have been assigned. 2. Note: Use the same balance for all the pennies of your mint year and record all masses to the full precision of the balance, 0.001g. Calculations: Penny Mass Mean: Compute the mean of penny masses: Mass Mean = (m 1 + m2 + ......mn ) n Standard Deviation: Compute the standard deviation of penny masses: sX = Where: (d12 + d 22 + d32 + ... + d n2 ) n -1 ... are the deviations of the measured mass values from the mean mass of all pennies. n is the number of pennies measured. The use of n-1 in the denominator in the calculation, especially for small normal populations, provides the best estimate of the population standard deviation Analysis & Conclusions: Address the following questions in you analysis and conclusions discussion 1. Do the variations in the average mass from year to year appear to vary significantly? 2. In what year was there a significant change in the mass of the penny? 3. What does this change in mass suggest? 4. Does the introduction of the Cu/Zn penny correlate with the change in penny mass noticed? 5. Did the standard deviation appear to change significantly in that year? 6. Provide an explanation for any change. Data Processing: Use the printed Pre-lab report as a notebook to record the mint year and penny masses in the results section of the applicable procedure. Summarize the experimental and computational results, including applicable spreadsheet computations, in the printed “Summary Results Table.” If required by the instructor, transfer the laboratory results to the electronic files and finalize the laboratory report. Spreadsheet Processing: Input Results into Laboratory Database Use one of the laboratory computers and the web-based data entry form shown in Figure 1 below to enter the mint year and penny masses into the laboratory database. Figure 1: Input Screen for entering Pennies results into laboratory Excel database Retrieve and Process Class Data Outside of class, retrieve the laboratory results for the entire class from the lab database: http://chem.gmu.edu/results Copy the data presented on the screen and insert into a spreadsheet (Excel, Google, other) and save the spreadsheet on your hard drive or flash drive with an appropriate file name. Your default “sheet” should be renamed (RawData) and have the following columnar format: Row Col A B C D E F G H I J K L m9 m10 Chemistry 211-2A1 Pennies and Good Sense 1 2 Year No. m1 m2 m3 m4 m5 m6 m7 m8 3 Column Explanations: A B Year No. C:L Mint Year Number of Pennies Measured m1- m10 Penny Mass (g) Create a new “sheet” for statistics computations: From the bottom of the “RawData” worksheet, add a new sheet and name it “Results.” Create the following columns in “Results” as indicated in the table below. Column D will be used to compute the standard deviation. Row Col 1 2 3 4 5 A B C Gen Chem 211 Sec 204 Pennies Standard Mint Mean Year Mass Deviation Copy Mint Year from “RawData” Sheet into Column A Enter algorithm for computing the mean mass of pennies in Column A Select cell B3: enter your algorithm Enter algorithm for computing the Standard Deviation of penny masses from the “RawData” sheet Select cell C3: enter your algorithm Compute results for all students Select cells A3:Cx (x = row number of last student) In Excel click on “Home” and select “Fill Down from “editing” box on right side of menu bar In Google Sheets press Ctrl D Create Scatter Plots of Mint Year vs. Mean Mass and Mint Year vs. Standard Deviation Select Data – Mint Year, Penny Mass Mean, Standard Deviation Select Cells A3:Cx (x = row number of last student in list) Create Scatter Plot Select “Insert Charts” Click on ”Scatter Plot” Modify Chart Type (Changes style) Under “Chart Tools” select Design Select last chart in list (Style “11”) Change “Series Chart Plot Type” (Adds secondary axis scale for Std Deviation) Right click anywhere in chart Select “Change Chart Type” Click “secondary axis” box for “series 2” (Std Deviation) Add Axis Title Boxes Click anywhere in chart Click on “+” symbol on right side of chart Select “Axis Titles” box Edit Axis Title Boxes Right click any axis/title box Click on “Font” Select text color (Black) Change Font size to appropriate size (12) Repeat for all text boxes Move “legend” to right side of chart Right click legend box Click “Right” box in “Format Legend” menu box on right side Edit legend box (names) Select “Legend” box Click on “Funnel” symbol on right side of chart Select “Series 1“ Click on “Edit” box Enter ”Mean Mass” Repeat for “Series 2 box (Std Deviation) Edit Legend Font (color) Right click Legend box Select “Font” Select color (Black) Adjust “Mean Mass” axis boundary Click on any right side axis scale value (Std Deviation) Select “Format Axis” in dialog box Change Boundary Maximum to 0.10 Add Trend line to each series Click on any data point in one of the series Select “Add Trendline” from list Check – Display Equation on Chart Note: Select and reposition equation as desired Check – R-Squared Value on Chart Note: Select and reposition R-Squared value as desired Repeat for the other series Results Summary Table Pennies & Good Sense Mint Year: Number of Pennies: Results Mass of Penny Sum of Masses (g): Mean of Mass (g): Standard Deviation (g): Class Results Year Mean Std Dev Year Mean Std Dev