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Copper Penny Lab Report - measuring density.

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Introduction

´╗┐Is it a Copper Penny? Measuring Density Experiment Date: 30 September 2010 Due Date: 8 October 2010 Is it a Copper Penny? Measuring Density Objective The objective of the experiment is to calculate the densities of pennies and determine the unknown compositions of pennies minted in 1943, and compare the accuracy and precision of the results to the known densities of pennies minted between 1962 and 1982 and those minted after 1982. Materials 1. Balance 2. 100 mL graduated cylinder 3. 35 pennies minted between 1962 and 1982 4. 35 pennies minted after 1982 5. 35 pennies minted during 1943 6. Paper towels Procedure 1. 2 pennies minted between 1962 and 1982 were placed and weighed for mass on a balance and the respective mass was recorded. 2. The 2 pennies were then placed in a graduated cylinder containing 20 mL of distilled water in order to find the volume of the pennies inside the water. 3. The displacement of the water, after the 2 pennies were added, was recorded as the volume. 4. Step 1 was repeated using a new set of 13 pennies minted between 1962 and 1982. 5. These 13 pennies were then added to the graduated cylinder containing 20 mL of distilled water and the set of 2 pennies. ...read more.

Middle

= 7.5 g/mL 35 (4.97 + 32.63 + 50.74) = 88.34 g 12.0 mL (88.34 g / 12.0 mL) = 7.4 g/mL Table 6: Pennies Minted During 1943 Number of Pennies Mass of Pennies Volume of Pennies Density (Mass/Volume) 2 5.52 g 2.0 mL (5.52 g / 2.0 mL) = 2.8 g/mL 15 (5.52 + 35.95) = 41.47 g 6.0 mL (41.47 g / 6.0) = 6.9 g/mL 35 (5.52 + 35.95 + 55.33) = 96.80 g 13.0 mL (96.80 g / 13.0 mL) = 7.4 g/mL Table 7: Theoretical Density Pennies minted between 1962 and 1982 Pennies minted after 1982 % Copper 95% 2.5% % Zinc 5% 97.5% Density of Copper 8.96 g/cm3 Density of Zinc 7.14 g/cm3 (% copper)(density of copper) + (% zinc)(density of zinc) (0.95)(8.96 g/cm3) + (0.05)(7.14 g/cm3) = 8.9 g/cm3 (0.025)(8.96 g/ cm3) + (0.975)(7.14 g/cm3) = 7.18 g/cm3 Table 8: Density Percent Errors Number of Pennies Theoretical Density Experimental Density Error = Theoretical-Actual Percent Error = |Error| / Theoretical x 100 Pennies minted between 1962 and 1982 2 8.9 6.2 8.9 - 6.2 = 2.7 (|2.7| / 8.9) x 100= 30.3% 15 8.9 9.2 8.9 - 9.2 = -0.3 (|-0.3| / 9.2) x 100= 3% 35 8.9 9.0 8.9 - 9.0 = -0.1 (|-0.1| / 8.9) ...read more.

Conclusion

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. ...read more.

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