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Preparing for the
All Things Google II
Assignment #1 - Writing in Chemistry
Concept Mapping Examples
Lab Safety Webquest
Drawing Graphs with Excel
Lab Conclusion Example
Pennies minted before 1982 exhibited an average density of 8.20 g/mL while pennies made since 1982 exhibited a density of 6.60 g/mL. The actual density of copper is 8.96 g/mL, thus no pennies tested in this experiment were composed of pure copper. However, pre-1982 pennies are the closest to pure copper. Analysis of the graph illustrates a linear relationship between mass and volume for both penny samples. This result matches the direct proportion (mass ∝ Volume) expected from the density where the slope of the line is the density. Pre-1982 pennies display a slightly higher slope than post-1982 pennies.
Pre-1982 pennies were made of an alloy composed of 95% copper and 5% zinc. Pennies made since 1982 have a zinc center covered with a thin layer of copper and are 97.6% zinc and 2.4% copper. This accounts for the difference in the mass and density of the penny samples.
Dropping pennies into a graduated cylinder filled with water causes a fair amount of turbulence. Tiny bubbles may have been trapped between the pennies resulting in a higher than actual volume reading. Another source of error lies in reading volume changes of few pennies. The precision of a 100-mL graduated cylinder is not enough to make an accurate determination of displacement.
To alleviate the possibility of trapped air, it is suggested the graduated cylinder be slightly tapped on the bottom thereby releasing any bubbles. Penny samples with greater numbers would increase the ease of reading displacement. In addition, the pennies should be inspected for cleanliness and uniformity in wear.
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