Download Experiment 1 Using Pennies and Good Sense

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