Table 2: Pennies Minted After 1982
Table 3: Pennies Minted During 1943
Densities of Different Metals
Analysis
Table 4: Pennies Minted Between 1962 and 1982
Table 5: Pennies Minted After 1982
Table 6: Pennies Minted During 1943
Table 7: Theoretical Density
Table 8: Density Percent Errors
Discussion
After the data was collected, which includes the mass of 2, 13, and 20 pennies from all three time periods, and the volumes of 2, 15, and 35 pennies from all three time periods, the densities of the 2, 15, and 35 pennies were calculated by dividing the volume from the mass (Density = mass/volume). The mass of the pennies was calculated by adding combinations of the masses that were recorded in step 1 of the procedure. The results are all recorded in tables 1 through 6.
Once the densities of 2, 15, and 35 pennies from the respective time periods were calculated, the theoretical densities for pennies minted between 1962 and 1982, and the pennies minted after 1982 were found. The theoretical densities were calculated by using the formula: (%zinc)(density of zinc) + (%copper)(density of copper). The theoretical density is calculated in table 7.
The percent errors of the densities were also calculated to compare the densities from the experiment with the accepted densities of the different pennies. This was important because the percent error assesses the accuracy of the experimental densities. As one can see from table 8, the percent errors were extremely high when experimenting with 2 pennies. However, the percent errors of 15 and 35 pennies are pretty low. This means that when experimenting with 2 pennies, the results were very off. On the other hand, as more pennies were experimented with, the results started to show more similar results to the theoretical values and became more accurate. According to the experiment, as the size of the sample increases, the accuracy of results also increases.
The last part of the lab is to determine the composition of pennies minted in 1943, which is the unknown. For the most accurate possible composition, the most accurate density must be used. The most accurate density would be 7.4 g/mL, which was calculated when the sample size was 35 pennies. Again, according to the experiment, the larger the sample size then, the more accurate the results. Therefore, the density of the 35 pennies minted in 1943, were compared to the chart labeled, Densities of Different Metals. Although, g/mL and g/cm3 use different units, the two are equal because 1 mL = 1 cm3. The metal with the most similar density was Manganese (Mn) with a density of 7.43 g/cm3 and somewhat similar to Tin (Sn) with a density of 7.51 g/cm3. These two metals are corrosion resistant, but still are susceptible to oxidation. Therefore, the next most probable metal would be Zinc (Zn) with a density of 7.14 g/cm3, which does not corrode or oxidize.
It is actually very interesting how the experimental densities of pennies minted after 1982 and in 1943 came out to both equal 7.4 g/cm3, when the density of pennies minted between 1962 and 1982 was much larger. However, because the percent error of the experimental densities of pennies minted after 1982 was higher, one can assume that this is the reason for this unusual result.
Overall, the results of the experiment were mostly reasonable. One change that would be made to the experiment if this experiment were to be repeated is that next time, when measuring the volumes of the pennies, the recorded numbers would be more accurate as such to not round the volume to the nearest mL. This way, the percent errors of the results may have been smaller. Also, the balances used were not as accurate because when the same 2 pennies were weighed twice, the two masses were different.
Conclusion
The lab was able to meet the main objective of this experiment, which was to estimate the unknown composition of the pennies minted in 1943 by analyzing and comparing data found and given of pennies minted from another two different time periods. Other than that, one could have learned from the experiment how to round off to the correct significant digit and becoming more comfortable when working with different densities and percent errors. Also, an important lesson learned from this particular experiment was that more accurate results could be achieved by using larger sample sizes when experimenting.