The Composition of Pennies Pre-1982 and Post-1982

Report
THE COMPOSITION OF
PENNIES PRE-1982 AND
POST-1982
Tim Cumming & Caitlin Carmody
Timeline of the Penny
• Composition pure Copper from 1793 to 1837
• From 1837 to 1857, 95 % Cu, 5 % Sn and Zn
• In 1857, 88 % Cu, 12 % Ni
• 1864 to 1962, 95 % Cu, 5 % Sn and Zn
• In 1962, 95 % Cu and 5 % Zn
• In 1982, 97.5 % Zn and 2.5 % Cu
Why did the composition change?
• The value of Copper increased (almost double) making
the government lose money when they produced pennies
• Zinc was, and still is, the most economical element to
make the coin
Objectives
• Use AA and ICP to determine the amount of Copper in
pennies from post and pre-1982
• Compare our results to the expected values of 95 %
Copper for pre-1982 and 2.5 % for post-1982
• Also compare that to the amount of Copper in dimes
within the same time periods, to see if the Copper
changes occurred in them too
Method
• Weighed out 20 coins (10 of each type) to determine
•
•
•
•
•
theoretical concentration of Cu
Dissolved 16 coins (8 of each type) in HNO3 (12 mL, 15
M, 48 h)
Made standards to correspond to theoretical
concentration of Cu
Diluted samples with distilled water
Ran samples through AA and ICP
Analyzed data provided
Coin Data
AA Standards
35
AA Cu Standards
30
y = 29.378x - 2.153
R² = 0.9948
Concentration (ppm))
25
20
15
10
5
0
0.000
0.200
0.400
0.600
Intensity (c/s))
0.800
1.000
1.200
AA Samples
75
AA Cu Samples
y = 29.378x - 2.153
R² = 1
70
Concentration (ppm)
65
60
55
50
45
40
1.500
1.700
1.900
2.100
Intensity (c/s)
2.300
2.500
2.700
Percent Error
Sample
% error
Dime SD
207.13
Penny SD
85.15
P8
57.78
P7
137.93
P2
131.38
P10
131.68
P1
890.11
P6
894.89
P9
605.36
P3
889.91
D1
308.70
D2
308.18
D3
308.47
D10
311.57
D4
311.32
D5
311.73
D6
323.21
D7
306.97
Average
362.30
ICP Standards
Concentration=0.0021(int)-0.3502
Concentration=0.00005(int)-0.5964
ICP Samples
Concentration=0.0021(int)-0.1795
Concentration=0.00005(int)-0.0522
Percent Error
Sample
D1
D2
D3
D4
D5
D6
D7
D10
P1
P2
P3
P6
P7
P8
P9
P10
Average
Excl D1
% Error
6876.237
27.97919
57.97085
83.26748
94.72858
95.24066
96.46304
97.1434
99.38568
99.78901
96.69686
96.8463
99.56288
99.37469
97.59604
99.99843
513.6425
89.46954
Sample
D1
D2
D3
D4
D5
D6
D7
D10
P1
P2
P3
P6
P7
P8
P9
P10
Average
Excl D1
% Error
2305.426
35.70609
33.41022
63.06946
93.46908
97.95354
99.18337
99.47421
95.79454
98.86611
92.39286
92.26862
98.51899
98.44154
94.47805
98.72543
224.8236
86.11681
Results
• The overall trend followed with our idea that as mass
increased, the Copper content would increase
• Also supported the theory that the composition changed
over the years, specifically from pre- to post-1982
• It is obvious that the samples were much higher than the
standards prepared, at least with the AA
• The ICP, being the ever-temperamental piece of
equipment that it is, gave the exact opposite results that
the AA produced
Conclusions
• It is inconclusive based on the data we obtained as per
the percentage of Cu in dimes and pennies
• Due to the many reasons on the next slide…
Problems
• Our standards did not match up to where we believed that
our samples would be
• The ICP seems to have changed its mind on the reading it
gave for a blank sample of distilled water between the
dates of 24/4 and 29/4
• We believe that we added to the burning of the torch head
of the ICP, and we are sorry for that, but if it is any
consolation, we didn’t get any reliable results, so it got us
back, immediately
Sources
• http://www.usmint.gov/about_the_mint/fun_facts/index.cfm
?flash=no&action=fun_facts2
• http://www.scholieren.com/proef/35020
Questions?

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